summaryrefslogtreecommitdiff
path: root/make.texinfo
blob: 7bbd1d289e347e1a3caf9be19fa742d0e35a69c5 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
3694
3695
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
3740
3741
3742
3743
3744
3745
3746
3747
3748
3749
3750
3751
3752
3753
3754
3755
3756
3757
3758
3759
3760
3761
3762
3763
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
3779
3780
3781
3782
3783
3784
3785
3786
3787
3788
3789
3790
3791
3792
3793
3794
3795
3796
3797
3798
3799
3800
3801
3802
3803
3804
3805
3806
3807
3808
3809
3810
3811
3812
3813
3814
3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
3829
3830
3831
3832
3833
3834
3835
3836
3837
3838
3839
3840
3841
3842
3843
3844
3845
3846
3847
3848
3849
3850
3851
3852
3853
3854
3855
3856
3857
3858
3859
3860
3861
3862
3863
3864
3865
3866
3867
3868
3869
3870
3871
3872
3873
3874
3875
3876
3877
3878
3879
3880
3881
3882
3883
3884
3885
3886
3887
3888
3889
3890
3891
3892
3893
3894
3895
3896
3897
3898
3899
3900
3901
3902
3903
3904
3905
3906
3907
3908
3909
3910
3911
3912
3913
3914
3915
3916
3917
3918
3919
3920
3921
3922
3923
3924
3925
3926
3927
3928
3929
3930
3931
3932
3933
3934
3935
3936
3937
3938
3939
3940
3941
3942
3943
3944
3945
3946
3947
3948
3949
3950
3951
3952
3953
3954
3955
3956
3957
3958
3959
3960
3961
3962
3963
3964
3965
3966
3967
3968
3969
3970
3971
3972
3973
3974
3975
3976
3977
3978
3979
3980
3981
3982
3983
3984
3985
3986
3987
3988
3989
3990
3991
3992
3993
3994
3995
3996
3997
3998
3999
4000
4001
4002
4003
4004
4005
4006
4007
4008
4009
4010
4011
4012
4013
4014
4015
4016
4017
4018
4019
4020
4021
4022
4023
4024
4025
4026
4027
4028
4029
4030
4031
4032
4033
4034
4035
4036
4037
4038
4039
4040
4041
4042
4043
4044
4045
4046
4047
4048
4049
4050
4051
4052
4053
4054
4055
4056
4057
4058
4059
4060
4061
4062
4063
4064
4065
4066
4067
4068
4069
4070
4071
4072
4073
4074
4075
4076
4077
4078
4079
4080
4081
4082
4083
4084
4085
4086
4087
4088
4089
4090
4091
4092
4093
4094
4095
4096
4097
4098
4099
4100
4101
4102
4103
4104
4105
4106
4107
4108
4109
4110
4111
4112
4113
4114
4115
4116
4117
4118
4119
4120
4121
4122
4123
4124
4125
4126
4127
4128
4129
4130
4131
4132
4133
4134
4135
4136
4137
4138
4139
4140
4141
4142
4143
4144
4145
4146
4147
4148
4149
4150
4151
4152
4153
4154
4155
4156
4157
4158
4159
4160
4161
4162
4163
4164
4165
4166
4167
4168
4169
4170
4171
4172
4173
4174
4175
4176
4177
4178
4179
4180
4181
4182
4183
4184
4185
4186
4187
4188
4189
4190
4191
4192
4193
4194
4195
4196
4197
4198
4199
4200
4201
4202
4203
4204
4205
4206
4207
4208
4209
4210
4211
4212
4213
4214
4215
4216
4217
4218
4219
4220
4221
4222
4223
4224
4225
4226
4227
4228
4229
4230
4231
4232
4233
4234
4235
4236
4237
4238
4239
4240
4241
4242
4243
4244
4245
4246
4247
4248
4249
4250
4251
4252
4253
4254
4255
4256
4257
4258
4259
4260
4261
4262
4263
4264
4265
4266
4267
4268
4269
4270
4271
4272
4273
4274
4275
4276
4277
4278
4279
4280
4281
4282
4283
4284
4285
4286
4287
4288
4289
4290
4291
4292
4293
4294
4295
4296
4297
4298
4299
4300
4301
4302
4303
4304
4305
4306
4307
4308
4309
4310
4311
4312
4313
4314
4315
4316
4317
4318
4319
4320
4321
4322
4323
4324
4325
4326
4327
4328
4329
4330
4331
4332
4333
4334
4335
4336
4337
4338
4339
4340
4341
4342
4343
4344
4345
4346
4347
4348
4349
4350
4351
4352
4353
4354
4355
4356
4357
4358
4359
4360
4361
4362
4363
4364
4365
4366
4367
4368
4369
4370
4371
4372
4373
4374
4375
4376
4377
4378
4379
4380
4381
4382
4383
4384
4385
4386
4387
4388
4389
4390
4391
4392
4393
4394
4395
4396
4397
4398
4399
4400
4401
4402
4403
4404
4405
4406
4407
4408
4409
4410
4411
4412
4413
4414
4415
4416
4417
4418
4419
4420
4421
4422
4423
4424
4425
4426
4427
4428
4429
4430
4431
4432
4433
4434
4435
4436
4437
4438
4439
4440
4441
4442
4443
4444
4445
4446
4447
4448
4449
4450
4451
4452
4453
4454
4455
4456
4457
4458
4459
4460
4461
4462
4463
4464
4465
4466
4467
4468
4469
4470
4471
4472
4473
4474
4475
4476
4477
4478
4479
4480
4481
4482
4483
4484
4485
4486
4487
4488
4489
4490
4491
4492
4493
4494
4495
4496
4497
4498
4499
4500
4501
4502
4503
4504
4505
4506
4507
4508
4509
4510
4511
4512
4513
4514
4515
4516
4517
4518
4519
4520
4521
4522
4523
4524
4525
4526
4527
4528
4529
4530
4531
4532
4533
4534
4535
4536
4537
4538
4539
4540
4541
4542
4543
4544
4545
4546
4547
4548
4549
4550
4551
4552
4553
4554
4555
4556
4557
4558
4559
4560
4561
4562
4563
4564
4565
4566
4567
4568
4569
4570
4571
4572
4573
4574
4575
4576
4577
4578
4579
4580
4581
4582
4583
4584
4585
4586
4587
4588
4589
4590
4591
4592
4593
4594
4595
4596
4597
4598
4599
4600
4601
4602
4603
4604
4605
4606
4607
4608
4609
4610
4611
4612
4613
4614
4615
4616
4617
4618
4619
4620
4621
4622
4623
4624
4625
4626
4627
4628
4629
4630
4631
4632
4633
4634
4635
4636
4637
4638
4639
4640
4641
4642
4643
4644
4645
4646
4647
4648
4649
4650
4651
4652
4653
4654
4655
4656
4657
4658
4659
4660
4661
4662
4663
4664
4665
4666
4667
4668
4669
4670
4671
4672
4673
4674
4675
4676
4677
4678
4679
4680
4681
4682
4683
4684
4685
4686
4687
4688
4689
4690
4691
4692
4693
4694
4695
4696
4697
4698
4699
4700
4701
4702
4703
4704
4705
4706
4707
4708
4709
4710
4711
4712
4713
4714
4715
4716
4717
4718
4719
4720
4721
4722
4723
4724
4725
4726
4727
4728
4729
4730
4731
4732
4733
4734
4735
4736
4737
4738
4739
4740
4741
4742
4743
4744
4745
4746
4747
4748
4749
4750
4751
4752
4753
4754
4755
4756
4757
4758
4759
4760
4761
4762
4763
4764
4765
4766
4767
4768
4769
4770
4771
4772
4773
4774
4775
4776
4777
4778
4779
4780
4781
4782
4783
4784
4785
4786
4787
4788
4789
4790
4791
4792
4793
4794
4795
4796
4797
4798
4799
4800
4801
4802
4803
4804
4805
4806
4807
4808
4809
4810
4811
4812
4813
4814
4815
4816
4817
4818
4819
4820
4821
4822
4823
4824
4825
4826
4827
4828
4829
4830
4831
4832
4833
4834
4835
4836
4837
4838
4839
4840
4841
4842
4843
4844
4845
4846
4847
4848
4849
4850
4851
4852
4853
4854
4855
4856
4857
4858
4859
4860
4861
4862
4863
4864
4865
4866
4867
4868
4869
4870
4871
4872
4873
4874
4875
4876
4877
4878
4879
4880
4881
4882
4883
4884
4885
4886
4887
4888
4889
4890
4891
4892
4893
4894
4895
4896
4897
4898
4899
4900
4901
4902
4903
4904
4905
4906
4907
4908
4909
4910
4911
4912
4913
4914
4915
4916
4917
4918
4919
4920
4921
4922
4923
4924
4925
4926
4927
4928
4929
4930
4931
4932
4933
4934
4935
4936
4937
4938
4939
4940
4941
4942
4943
4944
4945
4946
4947
4948
4949
4950
4951
4952
4953
4954
4955
4956
4957
4958
4959
4960
4961
4962
4963
4964
4965
4966
4967
4968
4969
4970
4971
4972
4973
4974
4975
4976
4977
4978
4979
4980
4981
4982
4983
4984
4985
4986
4987
4988
4989
4990
4991
4992
4993
4994
4995
4996
4997
4998
4999
5000
5001
5002
5003
5004
5005
5006
5007
5008
5009
5010
5011
5012
5013
5014
5015
5016
5017
5018
5019
5020
5021
5022
5023
5024
5025
5026
5027
5028
5029
5030
5031
5032
5033
5034
5035
5036
5037
5038
5039
5040
5041
5042
5043
5044
5045
5046
5047
5048
5049
5050
5051
5052
5053
5054
5055
5056
5057
5058
5059
5060
5061
5062
5063
5064
5065
5066
5067
5068
5069
5070
5071
5072
5073
5074
5075
5076
5077
5078
5079
5080
5081
5082
5083
5084
5085
5086
5087
5088
5089
5090
5091
5092
5093
5094
5095
5096
5097
5098
5099
5100
5101
5102
5103
5104
5105
5106
5107
5108
5109
5110
5111
5112
5113
5114
5115
5116
5117
5118
5119
5120
5121
5122
5123
5124
5125
5126
5127
5128
5129
5130
5131
5132
5133
5134
5135
5136
5137
5138
5139
5140
5141
5142
5143
5144
5145
5146
5147
5148
5149
5150
5151
5152
5153
5154
5155
5156
5157
5158
5159
5160
5161
5162
5163
5164
5165
5166
5167
5168
5169
5170
5171
5172
5173
5174
5175
5176
5177
5178
5179
5180
5181
5182
5183
5184
5185
5186
5187
5188
5189
5190
5191
5192
5193
5194
5195
5196
5197
5198
5199
5200
5201
5202
5203
5204
5205
5206
5207
5208
5209
5210
5211
5212
5213
5214
5215
5216
5217
5218
5219
5220
5221
5222
5223
5224
5225
5226
5227
5228
5229
5230
5231
5232
5233
5234
5235
5236
5237
5238
5239
5240
5241
5242
5243
5244
5245
5246
5247
5248
5249
5250
5251
5252
5253
5254
5255
5256
5257
5258
5259
5260
5261
5262
5263
5264
5265
5266
5267
5268
5269
5270
5271
5272
5273
5274
5275
5276
5277
5278
5279
5280
5281
5282
5283
5284
5285
5286
5287
5288
5289
5290
5291
5292
5293
5294
5295
5296
5297
5298
5299
5300
5301
5302
5303
5304
5305
5306
5307
5308
5309
5310
5311
5312
5313
5314
5315
5316
5317
5318
5319
5320
5321
5322
5323
5324
5325
5326
5327
5328
5329
5330
5331
5332
5333
5334
5335
5336
5337
5338
5339
5340
5341
5342
5343
5344
5345
5346
5347
5348
5349
5350
5351
5352
5353
5354
5355
5356
5357
5358
5359
5360
5361
5362
5363
5364
5365
5366
5367
5368
5369
5370
5371
5372
5373
5374
5375
5376
5377
5378
5379
5380
5381
5382
5383
5384
5385
5386
5387
5388
5389
5390
5391
5392
5393
5394
5395
5396
5397
5398
5399
5400
5401
5402
5403
5404
5405
5406
5407
5408
5409
5410
5411
5412
5413
5414
5415
5416
5417
5418
5419
5420
5421
5422
5423
5424
5425
5426
5427
5428
5429
5430
5431
5432
5433
5434
5435
5436
5437
5438
5439
5440
5441
5442
5443
5444
5445
5446
5447
5448
5449
5450
5451
5452
5453
5454
5455
5456
5457
5458
5459
5460
5461
5462
5463
5464
5465
5466
5467
5468
5469
5470
5471
5472
5473
5474
5475
5476
5477
5478
5479
5480
5481
5482
5483
5484
5485
5486
5487
5488
5489
5490
5491
5492
5493
5494
5495
5496
5497
5498
5499
5500
5501
5502
5503
5504
5505
5506
5507
5508
5509
5510
5511
5512
5513
5514
5515
5516
5517
5518
5519
5520
5521
5522
5523
5524
5525
5526
5527
5528
5529
5530
5531
5532
5533
5534
5535
5536
5537
5538
5539
5540
5541
5542
5543
5544
5545
5546
5547
5548
5549
5550
5551
5552
5553
5554
5555
5556
5557
5558
5559
5560
5561
5562
5563
5564
5565
5566
5567
5568
5569
5570
5571
5572
5573
5574
5575
5576
5577
5578
5579
5580
5581
5582
5583
5584
5585
5586
5587
5588
5589
5590
5591
5592
5593
5594
5595
5596
5597
5598
5599
5600
5601
5602
5603
5604
5605
5606
5607
5608
5609
5610
5611
5612
5613
5614
5615
5616
5617
5618
5619
5620
5621
5622
5623
5624
5625
5626
5627
5628
5629
5630
5631
5632
5633
5634
5635
5636
5637
5638
5639
5640
5641
5642
5643
5644
5645
5646
5647
5648
5649
5650
5651
5652
5653
5654
5655
5656
5657
5658
5659
5660
5661
5662
5663
5664
5665
5666
5667
5668
5669
5670
5671
5672
5673
5674
5675
5676
5677
5678
5679
5680
5681
5682
5683
5684
5685
5686
5687
5688
5689
5690
5691
5692
5693
5694
5695
5696
5697
5698
5699
5700
5701
5702
5703
5704
5705
5706
5707
5708
5709
5710
5711
5712
5713
5714
5715
5716
5717
5718
5719
5720
5721
5722
5723
5724
5725
5726
5727
5728
5729
5730
5731
5732
5733
5734
5735
5736
5737
5738
5739
5740
5741
5742
5743
5744
5745
5746
5747
5748
5749
5750
5751
5752
5753
5754
5755
5756
5757
5758
5759
5760
5761
5762
5763
5764
5765
5766
5767
5768
5769
5770
5771
5772
5773
5774
5775
5776
5777
5778
5779
5780
5781
5782
5783
5784
5785
5786
5787
5788
5789
5790
5791
5792
5793
5794
5795
5796
5797
5798
5799
5800
5801
5802
5803
5804
5805
5806
5807
5808
5809
5810
5811
5812
5813
5814
5815
5816
5817
5818
5819
5820
5821
5822
5823
5824
5825
5826
5827
5828
5829
5830
5831
5832
5833
5834
5835
5836
5837
5838
5839
5840
5841
5842
5843
5844
5845
5846
5847
5848
5849
5850
5851
5852
5853
5854
5855
5856
5857
5858
5859
5860
5861
5862
5863
5864
5865
5866
5867
5868
5869
5870
5871
5872
5873
5874
5875
5876
5877
5878
5879
5880
5881
5882
5883
5884
5885
5886
5887
5888
5889
5890
5891
5892
5893
5894
5895
5896
5897
5898
5899
5900
5901
5902
5903
5904
5905
5906
5907
5908
5909
5910
5911
5912
5913
5914
5915
5916
5917
5918
5919
5920
5921
5922
5923
5924
5925
5926
5927
5928
5929
5930
5931
5932
5933
5934
5935
5936
5937
5938
5939
5940
5941
5942
5943
5944
5945
5946
5947
5948
5949
5950
5951
5952
5953
5954
5955
5956
5957
5958
5959
5960
5961
5962
5963
5964
5965
5966
5967
5968
5969
5970
5971
5972
5973
5974
5975
5976
5977
5978
5979
5980
5981
5982
5983
5984
5985
5986
5987
5988
5989
5990
5991
5992
5993
5994
5995
5996
5997
5998
5999
6000
6001
6002
6003
6004
6005
6006
6007
6008
6009
6010
6011
6012
6013
6014
6015
6016
6017
6018
6019
6020
6021
6022
6023
6024
6025
6026
6027
6028
6029
6030
6031
6032
6033
6034
6035
6036
6037
6038
6039
6040
6041
6042
6043
6044
6045
6046
6047
6048
6049
6050
6051
6052
6053
6054
6055
6056
6057
6058
6059
6060
6061
6062
6063
6064
6065
6066
6067
6068
6069
6070
6071
6072
6073
6074
6075
6076
6077
6078
6079
6080
6081
6082
6083
6084
6085
6086
6087
6088
6089
6090
6091
6092
6093
6094
6095
6096
6097
6098
6099
6100
6101
6102
6103
6104
6105
6106
6107
6108
6109
6110
6111
6112
6113
6114
6115
6116
6117
6118
6119
6120
6121
6122
6123
6124
6125
6126
6127
6128
6129
6130
6131
6132
6133
6134
6135
6136
6137
6138
6139
6140
6141
6142
6143
6144
6145
6146
6147
6148
6149
6150
6151
6152
6153
6154
6155
6156
6157
6158
6159
6160
6161
6162
6163
6164
6165
6166
6167
6168
6169
6170
6171
6172
6173
6174
6175
6176
6177
6178
6179
6180
6181
6182
6183
6184
6185
6186
6187
6188
6189
6190
6191
6192
6193
6194
6195
6196
6197
6198
6199
6200
6201
6202
6203
6204
6205
6206
6207
6208
6209
6210
6211
6212
6213
6214
6215
6216
6217
6218
6219
6220
6221
6222
6223
6224
6225
6226
6227
6228
6229
6230
6231
6232
6233
6234
6235
6236
6237
6238
6239
6240
6241
6242
6243
6244
6245
6246
6247
6248
6249
6250
6251
6252
6253
6254
6255
6256
6257
6258
6259
6260
6261
6262
6263
6264
6265
6266
6267
6268
6269
6270
6271
6272
6273
6274
6275
6276
6277
6278
6279
6280
6281
6282
6283
6284
6285
6286
6287
6288
6289
6290
6291
6292
6293
6294
6295
6296
6297
6298
6299
6300
6301
6302
6303
6304
6305
6306
6307
6308
6309
6310
6311
6312
6313
6314
6315
6316
6317
6318
6319
6320
6321
6322
6323
6324
6325
6326
6327
6328
6329
6330
6331
6332
6333
6334
6335
6336
6337
6338
6339
6340
6341
6342
6343
6344
6345
6346
6347
6348
6349
6350
6351
6352
6353
6354
6355
6356
6357
6358
6359
6360
6361
6362
6363
6364
6365
6366
6367
6368
6369
6370
6371
6372
6373
6374
6375
6376
6377
6378
6379
6380
6381
6382
6383
6384
6385
6386
6387
6388
6389
6390
6391
6392
6393
6394
6395
6396
6397
6398
6399
6400
6401
6402
6403
6404
6405
6406
6407
6408
6409
6410
6411
6412
6413
6414
6415
6416
6417
6418
6419
6420
6421
6422
6423
6424
6425
6426
6427
6428
6429
6430
6431
6432
6433
6434
6435
6436
6437
6438
6439
6440
6441
6442
6443
6444
6445
6446
6447
6448
6449
6450
6451
6452
6453
6454
6455
6456
6457
6458
6459
6460
6461
6462
6463
6464
6465
6466
6467
6468
6469
6470
6471
6472
6473
6474
6475
6476
6477
6478
6479
6480
6481
6482
6483
6484
6485
6486
6487
6488
6489
6490
6491
6492
6493
6494
6495
6496
6497
6498
6499
6500
6501
6502
6503
6504
6505
6506
6507
6508
6509
6510
6511
6512
6513
6514
6515
6516
6517
6518
6519
6520
6521
6522
6523
6524
6525
6526
6527
6528
6529
6530
6531
6532
6533
6534
6535
6536
6537
6538
6539
6540
6541
6542
6543
6544
6545
6546
6547
6548
6549
6550
6551
6552
6553
6554
6555
6556
6557
6558
6559
6560
6561
6562
6563
6564
6565
6566
6567
6568
6569
6570
6571
6572
6573
6574
6575
6576
6577
6578
6579
6580
6581
6582
6583
6584
6585
6586
6587
6588
6589
6590
6591
6592
6593
6594
6595
6596
6597
6598
6599
6600
6601
6602
6603
6604
6605
6606
6607
6608
6609
6610
6611
6612
6613
6614
6615
6616
6617
6618
6619
6620
6621
6622
6623
6624
6625
6626
6627
6628
6629
6630
6631
6632
6633
6634
6635
6636
6637
6638
6639
6640
6641
6642
6643
6644
6645
6646
6647
6648
6649
6650
6651
6652
6653
6654
6655
6656
6657
6658
6659
6660
6661
6662
6663
6664
6665
6666
6667
6668
6669
6670
6671
6672
6673
6674
6675
6676
6677
6678
6679
6680
6681
6682
6683
6684
6685
6686
6687
6688
6689
6690
6691
6692
6693
6694
6695
6696
6697
6698
6699
6700
6701
6702
6703
6704
6705
6706
6707
6708
6709
6710
6711
6712
6713
6714
6715
6716
6717
6718
6719
6720
6721
6722
6723
6724
6725
6726
6727
6728
6729
6730
6731
6732
6733
6734
6735
6736
6737
6738
6739
6740
6741
6742
6743
6744
6745
6746
6747
6748
6749
6750
6751
6752
6753
6754
6755
6756
6757
6758
6759
6760
6761
6762
6763
6764
6765
6766
6767
6768
6769
6770
6771
6772
6773
6774
6775
6776
6777
6778
6779
6780
6781
6782
6783
6784
6785
6786
6787
6788
6789
6790
6791
6792
6793
6794
6795
6796
6797
6798
6799
6800
6801
6802
6803
6804
6805
6806
6807
6808
6809
6810
6811
6812
6813
6814
6815
6816
6817
6818
6819
6820
6821
6822
6823
6824
6825
6826
6827
6828
6829
6830
6831
6832
6833
6834
6835
6836
6837
6838
6839
6840
6841
6842
6843
6844
6845
6846
6847
6848
6849
6850
6851
6852
6853
6854
6855
6856
6857
6858
6859
6860
6861
6862
6863
6864
6865
6866
6867
6868
6869
6870
6871
6872
6873
6874
6875
6876
6877
6878
6879
6880
6881
6882
6883
6884
6885
6886
6887
6888
6889
6890
6891
6892
6893
6894
6895
6896
6897
6898
6899
6900
6901
6902
6903
6904
6905
6906
6907
6908
6909
6910
6911
6912
6913
6914
6915
6916
6917
6918
6919
6920
6921
6922
6923
6924
6925
6926
6927
6928
6929
6930
6931
6932
6933
6934
6935
6936
6937
6938
6939
6940
6941
6942
6943
6944
6945
6946
6947
6948
6949
6950
6951
6952
6953
6954
6955
6956
6957
6958
6959
6960
6961
6962
6963
6964
6965
6966
6967
6968
6969
6970
6971
6972
6973
6974
6975
6976
6977
6978
6979
6980
6981
6982
6983
6984
6985
6986
6987
6988
6989
6990
6991
6992
6993
6994
6995
6996
6997
6998
6999
7000
7001
7002
7003
7004
7005
7006
7007
7008
7009
7010
7011
7012
7013
7014
7015
7016
7017
7018
7019
7020
7021
7022
7023
7024
7025
7026
7027
7028
7029
7030
7031
7032
7033
7034
7035
7036
7037
7038
7039
7040
7041
7042
7043
7044
7045
7046
7047
7048
7049
7050
7051
7052
7053
7054
7055
7056
7057
7058
7059
7060
7061
7062
7063
7064
7065
7066
7067
7068
7069
7070
7071
7072
7073
7074
7075
7076
7077
7078
7079
7080
7081
7082
7083
7084
7085
7086
7087
7088
7089
7090
7091
7092
7093
7094
7095
7096
7097
7098
7099
7100
7101
7102
7103
7104
7105
7106
7107
7108
7109
7110
7111
7112
7113
7114
7115
7116
7117
7118
7119
7120
7121
7122
7123
7124
7125
7126
7127
7128
7129
7130
7131
7132
7133
7134
7135
7136
7137
7138
7139
7140
7141
7142
7143
7144
7145
7146
7147
7148
7149
7150
7151
7152
7153
7154
7155
7156
7157
7158
7159
7160
7161
7162
7163
7164
7165
7166
7167
7168
7169
7170
7171
7172
7173
7174
7175
7176
7177
7178
7179
7180
7181
7182
7183
7184
7185
7186
7187
7188
7189
7190
7191
7192
7193
7194
7195
7196
7197
7198
7199
7200
7201
7202
7203
7204
7205
7206
7207
7208
7209
7210
7211
7212
7213
7214
7215
7216
7217
7218
7219
7220
7221
7222
7223
7224
7225
7226
7227
7228
7229
7230
7231
7232
7233
7234
7235
7236
7237
7238
7239
7240
7241
7242
7243
7244
7245
7246
7247
7248
7249
7250
7251
7252
7253
7254
7255
7256
7257
7258
7259
7260
7261
7262
7263
7264
7265
7266
7267
7268
7269
7270
7271
7272
7273
7274
7275
7276
7277
7278
7279
7280
7281
7282
7283
7284
7285
7286
7287
7288
7289
7290
7291
7292
7293
7294
7295
7296
7297
7298
7299
7300
7301
7302
7303
7304
7305
7306
7307
7308
7309
7310
7311
7312
7313
7314
7315
7316
7317
7318
7319
7320
7321
7322
7323
7324
7325
7326
7327
7328
7329
7330
7331
7332
7333
7334
7335
7336
7337
7338
7339
7340
7341
7342
7343
7344
7345
7346
7347
7348
7349
7350
7351
7352
7353
7354
7355
7356
7357
7358
7359
7360
7361
7362
7363
7364
7365
7366
7367
7368
7369
7370
7371
7372
7373
7374
7375
7376
7377
7378
7379
7380
7381
7382
7383
7384
7385
7386
7387
7388
7389
7390
7391
7392
7393
7394
7395
7396
7397
7398
7399
7400
7401
7402
7403
7404
7405
7406
7407
7408
7409
7410
7411
7412
7413
7414
7415
7416
7417
7418
7419
7420
7421
7422
7423
7424
7425
7426
7427
7428
7429
7430
7431
7432
7433
7434
7435
7436
7437
7438
7439
7440
7441
7442
7443
7444
7445
7446
7447
7448
7449
7450
7451
7452
7453
7454
7455
7456
7457
7458
7459
7460
7461
7462
7463
7464
7465
7466
7467
7468
7469
7470
7471
7472
7473
7474
7475
7476
7477
7478
7479
7480
7481
7482
7483
7484
7485
7486
7487
7488
7489
7490
7491
7492
7493
7494
7495
7496
7497
7498
7499
7500
7501
7502
7503
7504
7505
7506
7507
7508
7509
7510
7511
7512
7513
7514
7515
7516
7517
7518
7519
7520
7521
7522
7523
7524
7525
7526
7527
7528
7529
7530
7531
7532
7533
7534
7535
7536
7537
7538
7539
7540
7541
7542
7543
7544
7545
7546
7547
7548
7549
7550
7551
7552
7553
7554
7555
7556
7557
7558
7559
7560
7561
7562
7563
7564
7565
7566
7567
7568
7569
7570
7571
7572
7573
7574
7575
7576
7577
7578
7579
7580
7581
7582
7583
7584
7585
7586
7587
7588
7589
7590
7591
7592
7593
7594
7595
7596
7597
7598
7599
7600
7601
7602
7603
7604
7605
7606
7607
7608
7609
7610
7611
7612
7613
7614
7615
7616
7617
7618
7619
7620
7621
7622
7623
7624
7625
7626
7627
7628
7629
7630
7631
7632
7633
7634
7635
7636
7637
7638
7639
7640
7641
7642
7643
7644
7645
7646
7647
7648
7649
7650
7651
7652
7653
7654
7655
7656
7657
7658
7659
7660
7661
7662
7663
7664
7665
7666
7667
7668
7669
7670
7671
7672
7673
7674
7675
7676
7677
7678
7679
7680
7681
7682
7683
7684
7685
7686
7687
7688
7689
7690
7691
7692
7693
7694
7695
7696
7697
7698
7699
7700
7701
7702
7703
7704
7705
7706
7707
7708
7709
7710
7711
7712
7713
7714
7715
7716
7717
7718
7719
7720
7721
7722
7723
7724
7725
7726
7727
7728
7729
7730
7731
7732
7733
7734
7735
7736
7737
7738
7739
7740
7741
7742
7743
7744
7745
7746
7747
7748
7749
7750
7751
7752
7753
7754
7755
7756
7757
7758
7759
7760
7761
7762
7763
7764
7765
7766
7767
7768
7769
7770
7771
7772
7773
7774
7775
7776
7777
7778
7779
7780
7781
7782
7783
7784
7785
7786
7787
7788
7789
7790
7791
7792
7793
7794
7795
7796
7797
7798
7799
7800
7801
7802
7803
7804
7805
7806
7807
7808
7809
7810
7811
7812
7813
7814
7815
7816
7817
7818
7819
7820
7821
7822
7823
7824
7825
7826
7827
7828
7829
7830
7831
7832
7833
7834
7835
7836
7837
7838
7839
7840
7841
7842
7843
7844
7845
7846
7847
7848
7849
7850
7851
7852
7853
7854
7855
7856
7857
7858
7859
7860
7861
7862
7863
7864
7865
7866
7867
7868
7869
7870
7871
7872
7873
7874
7875
7876
7877
7878
7879
7880
7881
7882
7883
7884
7885
7886
7887
7888
7889
7890
7891
7892
7893
7894
7895
7896
7897
7898
7899
7900
7901
7902
7903
7904
7905
7906
7907
7908
7909
7910
7911
7912
7913
7914
7915
7916
7917
7918
7919
7920
7921
7922
7923
7924
7925
7926
7927
7928
7929
7930
7931
7932
7933
7934
7935
7936
7937
7938
7939
7940
7941
7942
7943
7944
7945
7946
7947
7948
7949
7950
7951
7952
7953
7954
7955
7956
7957
7958
7959
7960
7961
7962
7963
7964
7965
7966
7967
7968
7969
7970
7971
7972
7973
7974
7975
7976
7977
7978
7979
7980
7981
7982
7983
7984
7985
7986
7987
7988
7989
7990
7991
7992
7993
7994
7995
7996
7997
7998
7999
8000
8001
8002
8003
8004
8005
8006
8007
8008
8009
8010
8011
8012
8013
8014
8015
8016
8017
8018
8019
8020
8021
8022
8023
8024
8025
8026
8027
8028
8029
8030
8031
8032
8033
8034
8035
8036
8037
8038
8039
8040
8041
8042
8043
8044
8045
8046
8047
8048
8049
8050
8051
8052
8053
8054
8055
8056
8057
8058
8059
8060
8061
8062
8063
8064
8065
8066
8067
8068
8069
8070
8071
8072
8073
8074
8075
8076
8077
8078
8079
8080
8081
8082
8083
8084
8085
8086
8087
8088
8089
8090
8091
8092
8093
8094
8095
8096
8097
8098
8099
8100
8101
8102
8103
8104
8105
8106
8107
8108
8109
8110
8111
8112
8113
8114
8115
8116
8117
8118
8119
8120
8121
8122
8123
8124
8125
8126
8127
8128
8129
8130
8131
8132
8133
8134
8135
8136
8137
8138
8139
8140
8141
8142
8143
8144
8145
8146
8147
8148
8149
8150
8151
8152
8153
8154
8155
8156
8157
8158
8159
8160
8161
8162
8163
8164
8165
8166
8167
8168
8169
8170
8171
8172
8173
8174
8175
8176
8177
8178
8179
8180
8181
8182
8183
8184
8185
8186
8187
8188
8189
8190
8191
8192
8193
8194
8195
8196
8197
8198
8199
8200
8201
8202
8203
8204
8205
8206
8207
8208
8209
8210
8211
8212
8213
8214
8215
8216
8217
8218
8219
8220
8221
8222
8223
8224
8225
8226
8227
8228
8229
8230
8231
8232
8233
8234
8235
8236
8237
8238
8239
8240
8241
8242
8243
8244
8245
8246
8247
8248
8249
8250
8251
8252
8253
8254
8255
8256
8257
8258
8259
8260
8261
8262
8263
8264
8265
8266
8267
8268
8269
8270
8271
8272
8273
8274
8275
8276
8277
8278
8279
8280
8281
8282
8283
8284
8285
8286
8287
8288
8289
8290
8291
8292
8293
8294
8295
8296
8297
8298
8299
8300
8301
8302
8303
8304
8305
8306
8307
8308
8309
8310
8311
8312
8313
8314
8315
8316
8317
8318
8319
8320
8321
8322
8323
8324
8325
8326
8327
8328
8329
8330
8331
8332
8333
8334
8335
8336
8337
8338
8339
8340
8341
8342
8343
8344
8345
8346
8347
8348
8349
8350
8351
8352
8353
8354
8355
8356
8357
8358
8359
8360
8361
8362
8363
8364
8365
8366
8367
8368
8369
8370
8371
8372
8373
8374
8375
8376
8377
8378
8379
8380
8381
8382
8383
8384
8385
8386
8387
8388
8389
8390
8391
8392
8393
8394
8395
8396
8397
8398
8399
8400
8401
8402
8403
8404
8405
8406
8407
8408
8409
8410
8411
8412
8413
8414
8415
8416
8417
8418
8419
8420
8421
8422
8423
8424
8425
8426
8427
8428
8429
8430
8431
8432
8433
8434
8435
8436
8437
8438
8439
8440
8441
8442
8443
8444
8445
8446
8447
8448
8449
8450
8451
8452
8453
8454
8455
8456
8457
8458
8459
8460
8461
8462
8463
8464
8465
8466
8467
8468
8469
8470
8471
8472
8473
8474
8475
8476
8477
8478
8479
8480
8481
8482
8483
8484
8485
8486
8487
8488
8489
8490
8491
8492
8493
8494
8495
8496
8497
8498
8499
8500
8501
8502
8503
8504
8505
8506
8507
8508
8509
8510
8511
8512
8513
8514
8515
8516
8517
8518
8519
8520
8521
8522
8523
8524
8525
8526
8527
8528
8529
8530
8531
8532
8533
8534
8535
8536
8537
8538
8539
8540
8541
8542
8543
8544
8545
8546
8547
8548
8549
8550
8551
8552
8553
8554
8555
8556
8557
8558
8559
8560
8561
8562
8563
8564
8565
8566
8567
8568
8569
8570
8571
8572
8573
8574
8575
8576
8577
8578
8579
8580
8581
8582
8583
8584
8585
8586
8587
8588
8589
8590
8591
8592
8593
8594
8595
8596
8597
8598
8599
8600
8601
8602
8603
8604
8605
8606
8607
8608
8609
8610
8611
8612
8613
8614
8615
8616
8617
8618
8619
8620
8621
8622
8623
8624
8625
8626
8627
8628
8629
8630
8631
8632
8633
8634
8635
8636
8637
8638
8639
8640
8641
8642
8643
8644
8645
8646
8647
8648
8649
8650
8651
8652
8653
8654
8655
8656
8657
8658
8659
8660
8661
8662
8663
8664
8665
8666
8667
8668
8669
8670
8671
8672
8673
8674
8675
8676
8677
8678
8679
8680
8681
8682
8683
8684
8685
8686
8687
8688
8689
8690
8691
8692
8693
8694
8695
8696
8697
8698
8699
8700
8701
8702
8703
8704
8705
8706
8707
8708
8709
8710
8711
8712
8713
8714
8715
8716
8717
8718
8719
8720
8721
8722
8723
8724
8725
8726
8727
8728
8729
8730
8731
8732
8733
8734
8735
8736
8737
8738
8739
8740
8741
8742
8743
8744
8745
8746
8747
8748
8749
8750
8751
8752
8753
8754
8755
8756
8757
8758
8759
8760
8761
8762
8763
8764
8765
8766
8767
8768
8769
8770
8771
8772
8773
8774
8775
8776
8777
8778
8779
8780
8781
8782
8783
8784
8785
8786
8787
8788
8789
8790
8791
8792
8793
8794
8795
8796
8797
8798
8799
8800
8801
8802
8803
8804
8805
8806
8807
8808
8809
8810
8811
8812
8813
8814
8815
8816
8817
8818
8819
8820
8821
8822
8823
8824
8825
8826
8827
8828
8829
8830
8831
8832
8833
8834
8835
8836
8837
8838
8839
8840
8841
8842
8843
8844
8845
8846
8847
8848
8849
8850
8851
8852
8853
8854
8855
8856
8857
8858
8859
8860
8861
8862
8863
8864
8865
8866
8867
8868
8869
8870
8871
8872
8873
8874
8875
8876
8877
8878
8879
8880
8881
8882
8883
8884
8885
8886
8887
8888
8889
8890
8891
8892
8893
8894
8895
8896
8897
8898
8899
8900
8901
8902
8903
8904
8905
8906
8907
8908
8909
8910
8911
8912
8913
8914
8915
8916
8917
8918
8919
8920
8921
8922
8923
8924
8925
8926
8927
8928
8929
8930
8931
8932
8933
8934
8935
8936
8937
8938
8939
8940
8941
8942
8943
8944
8945
8946
8947
8948
8949
8950
8951
8952
8953
8954
8955
8956
8957
8958
8959
8960
8961
8962
8963
8964
8965
8966
8967
8968
8969
8970
8971
8972
8973
8974
8975
8976
8977
8978
8979
8980
8981
8982
8983
8984
8985
8986
8987
8988
8989
8990
8991
8992
8993
8994
8995
8996
8997
8998
8999
9000
9001
9002
9003
9004
9005
9006
9007
9008
9009
9010
9011
9012
9013
9014
9015
9016
9017
9018
9019
9020
9021
9022
9023
9024
9025
9026
9027
9028
9029
9030
9031
9032
9033
9034
9035
9036
9037
9038
9039
9040
9041
9042
9043
9044
9045
9046
9047
9048
9049
9050
9051
9052
9053
9054
9055
9056
9057
9058
9059
9060
9061
9062
9063
9064
9065
9066
9067
9068
9069
9070
9071
9072
9073
9074
9075
9076
9077
9078
9079
9080
9081
9082
9083
9084
9085
9086
9087
9088
9089
9090
9091
9092
9093
9094
9095
9096
9097
9098
9099
9100
9101
9102
9103
9104
9105
9106
9107
9108
9109
9110
9111
9112
9113
9114
9115
9116
9117
9118
9119
9120
9121
9122
9123
9124
9125
9126
9127
9128
9129
9130
9131
9132
9133
9134
9135
9136
9137
9138
9139
9140
9141
9142
9143
9144
9145
9146
9147
9148
9149
9150
9151
9152
9153
9154
9155
9156
9157
9158
9159
9160
9161
9162
9163
9164
9165
9166
9167
9168
9169
9170
9171
9172
9173
9174
9175
9176
9177
9178
9179
9180
9181
9182
9183
9184
9185
9186
9187
9188
9189
9190
9191
9192
9193
9194
9195
9196
9197
9198
9199
9200
9201
9202
9203
9204
9205
9206
9207
9208
9209
9210
9211
9212
9213
9214
9215
9216
9217
9218
9219
9220
9221
9222
9223
9224
9225
9226
9227
9228
9229
9230
9231
9232
9233
9234
9235
9236
9237
9238
9239
9240
9241
9242
9243
9244
9245
9246
9247
9248
9249
9250
9251
9252
9253
9254
9255
9256
9257
9258
9259
9260
9261
9262
9263
9264
9265
9266
9267
9268
9269
9270
9271
9272
9273
9274
9275
9276
9277
9278
9279
9280
9281
9282
9283
9284
9285
9286
9287
9288
9289
9290
9291
9292
9293
9294
9295
9296
9297
9298
9299
9300
9301
9302
9303
9304
9305
9306
9307
9308
9309
9310
9311
9312
9313
9314
9315
9316
9317
9318
9319
9320
9321
9322
9323
9324
9325
9326
9327
9328
9329
9330
9331
9332
9333
9334
9335
9336
9337
9338
9339
9340
9341
9342
9343
9344
9345
9346
9347
9348
9349
9350
9351
9352
9353
9354
9355
9356
9357
9358
9359
9360
9361
9362
9363
9364
9365
9366
9367
9368
9369
9370
9371
9372
9373
9374
9375
9376
9377
9378
9379
9380
9381
9382
9383
9384
9385
9386
9387
9388
9389
9390
9391
9392
9393
9394
9395
9396
9397
9398
9399
9400
9401
9402
9403
9404
9405
9406
9407
9408
9409
9410
9411
9412
9413
9414
9415
9416
9417
9418
9419
9420
9421
9422
9423
9424
9425
9426
9427
9428
9429
9430
9431
9432
9433
9434
9435
9436
9437
9438
9439
9440
9441
9442
9443
9444
9445
9446
9447
9448
9449
9450
9451
9452
9453
9454
9455
9456
9457
9458
9459
9460
9461
9462
9463
9464
9465
9466
9467
9468
9469
9470
9471
9472
9473
9474
9475
9476
9477
9478
9479
9480
9481
9482
9483
9484
9485
9486
9487
9488
9489
9490
9491
9492
9493
9494
9495
9496
9497
9498
9499
9500
9501
9502
9503
9504
9505
9506
9507
9508
9509
9510
9511
9512
9513
9514
9515
9516
9517
9518
9519
9520
9521
9522
9523
9524
9525
9526
9527
9528
9529
9530
9531
9532
9533
9534
9535
9536
9537
9538
9539
9540
9541
9542
9543
9544
9545
9546
9547
9548
9549
9550
9551
9552
9553
9554
9555
9556
9557
9558
9559
9560
9561
9562
9563
9564
9565
9566
9567
9568
9569
9570
9571
9572
9573
9574
9575
9576
9577
9578
9579
9580
9581
9582
9583
9584
9585
9586
9587
9588
9589
9590
9591
9592
9593
9594
9595
9596
9597
9598
9599
9600
9601
9602
9603
9604
9605
9606
9607
9608
9609
9610
9611
9612
9613
9614
9615
9616
9617
9618
9619
9620
9621
9622
9623
9624
9625
9626
9627
9628
9629
9630
9631
9632
9633
9634
9635
9636
9637
9638
9639
9640
9641
9642
9643
9644
9645
9646
9647
9648
9649
9650
9651
9652
9653
9654
9655
9656
9657
9658
9659
9660
9661
9662
9663
9664
9665
9666
9667
9668
9669
9670
9671
9672
9673
9674
9675
9676
9677
9678
9679
9680
9681
9682
9683
9684
9685
9686
9687
9688
9689
9690
9691
9692
9693
9694
9695
9696
9697
9698
9699
9700
9701
9702
9703
9704
9705
9706
9707
9708
9709
9710
9711
9712
9713
9714
9715
9716
9717
9718
9719
9720
9721
9722
9723
9724
9725
9726
9727
9728
9729
9730
9731
9732
9733
9734
9735
9736
9737
9738
9739
9740
9741
9742
9743
9744
9745
9746
9747
9748
9749
9750
9751
9752
9753
9754
9755
9756
9757
9758
9759
9760
9761
9762
9763
9764
9765
9766
9767
9768
9769
9770
9771
9772
9773
9774
9775
9776
9777
9778
9779
9780
9781
9782
9783
9784
9785
9786
9787
9788
9789
9790
9791
9792
9793
9794
9795
9796
9797
9798
9799
9800
9801
9802
9803
9804
9805
9806
9807
9808
9809
9810
9811
9812
9813
9814
9815
9816
9817
9818
9819
9820
9821
9822
9823
9824
9825
9826
9827
9828
9829
9830
9831
9832
9833
9834
9835
9836
9837
9838
9839
9840
9841
9842
9843
9844
9845
9846
9847
9848
9849
9850
9851
9852
9853
9854
9855
9856
9857
9858
9859
9860
9861
9862
9863
9864
9865
9866
9867
9868
9869
9870
9871
9872
9873
9874
9875
9876
9877
9878
9879
9880
9881
9882
9883
9884
9885
9886
9887
9888
9889
9890
9891
9892
9893
9894
9895
9896
9897
9898
9899
9900
9901
9902
9903
9904
9905
9906
9907
9908
9909
9910
9911
9912
\input texinfo                @c -*- Texinfo -*-
@c %**start of header
@setfilename make.info
@settitle GNU @code{make}
@setchapternewpage odd
@c %**end of header

@c FSF publishers: format makebook.texi instead of using this file directly.

@set RCSID $Id$
@set EDITION 0.55
@set VERSION 3.79
@set UPDATED 04 April 2000
@set UPDATE-MONTH April 2000
@comment The ISBN number might need to change on next publication.
@set ISBN 1-882114-80-9 @c CHANGE THIS BEFORE PRINTING AGAIN! --psmith 16jul98

@c finalout

@c ISPELL CHECK: done, 10 June 1993 --roland

@c Combine the variable and function indices:
@syncodeindex vr fn
@c Combine the program and concept indices:
@syncodeindex pg cp

@dircategory GNU Packages
@direntry
* Make: (make).            Remake files automatically.
@end direntry

@ifinfo
This file documents the GNU Make utility, which determines
automatically which pieces of a large program need to be recompiled,
and issues the commands to recompile them.

This is Edition @value{EDITION}, last updated @value{UPDATED},
of @cite{The GNU Make Manual}, for @code{make}, Version @value{VERSION}.

Copyright (C) 1988, '89, '90, '91, '92, '93, '94, '95, '96, '97, '98, '99, 2000
        Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

@ignore
Permission is granted to process this file through TeX and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).

@end ignore
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation approved
by the Free Software Foundation.
@end ifinfo

@iftex
@shorttitlepage GNU Make
@end iftex
@titlepage
@title GNU Make
@subtitle A Program for Directing Recompilation
@subtitle GNU @code{make} Version @value{VERSION}
@subtitle @value{UPDATE-MONTH}
@author Richard M. Stallman and Roland McGrath
@page
@vskip 0pt plus 1filll
Copyright @copyright{} 1988, '89, '90, '91, '92, '93, '94, '95, '96, '97, '98, '99, 2000
Free Software Foundation, Inc.
@sp 2
Published by the Free Software Foundation @*
59 Temple Place -- Suite 330, @*
Boston, MA 02111-1307 USA @*
ISBN @value{ISBN} @*

Maintenance and updates since Version 3.76 by Paul D. Smith.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation approved
by the Free Software Foundation.
@sp 2
Cover art by Etienne Suvasa.
@end titlepage
@page

@ifinfo
@node Top, Overview, , (dir)
@top Make

The GNU @code{make} utility automatically determines which pieces of a
large program need to be recompiled, and issues the commands to
recompile them.@refill

This edition of the @cite{GNU Make Manual},
last updated @value{UPDATED},
documents GNU @code{make} Version @value{VERSION}.@refill

This manual describes @code{make} and contains the following chapters:@refill
@end ifinfo

@menu
* Overview::                    Overview of @code{make}.
* Introduction::                An introduction to @code{make}.
* Makefiles::                   Makefiles tell @code{make} what to do.
* Rules::                       Rules describe when a file must be remade.
* Commands::                    Commands say how to remake a file.
* Using Variables::             You can use variables to avoid repetition.
* Conditionals::                Use or ignore parts of the makefile based
                                 on the values of variables.
* Functions::                   Many powerful ways to manipulate text.
* Invoking make: Running.       How to invoke @code{make} on the command line.
* Implicit Rules::              Use implicit rules to treat many files alike,
                                 based on their file names.
* Archives::                    How @code{make} can update library archives.
* Features::                    Features GNU @code{make} has over other @code{make}s.
* Missing::                     What GNU @code{make} lacks from other @code{make}s.
* Makefile Conventions::        Conventions for makefiles in GNU programs.
* Quick Reference::             A quick reference for experienced users.
* Error Messages::              A list of common errors generated by @code{make}.
* Complex Makefile::            A real example of a straightforward,
                                 but nontrivial, makefile.
* Concept Index::               Index of Concepts
* Name Index::                  Index of Functions, Variables, & Directives

 --- The Detailed Node Listing ---

Overview of @code{make}

* Preparing::                   Preparing and Running Make
* Reading::                     On Reading this Text
* Bugs::                        Problems and Bugs

An Introduction to Makefiles

* Rule Introduction::           What a rule looks like.
* Simple Makefile::             A Simple Makefile
* How Make Works::              How @code{make} Processes This Makefile
* Variables Simplify::          Variables Make Makefiles Simpler
* make Deduces::                Letting @code{make} Deduce the Commands
* Combine By Prerequisite::     Another Style of Makefile
* Cleanup::                     Rules for Cleaning the Directory

Writing Makefiles

* Makefile Contents::           What makefiles contain.
* Makefile Names::              How to name your makefile.
* Include::                     How one makefile can use another makefile.
* MAKEFILES Variable::          The environment can specify extra makefiles.
* Remaking Makefiles::          How makefiles get remade.
* Overriding Makefiles::        How to override part of one makefile
                                 with another makefile.
* Reading Makefiles::           How makefiles are parsed.

Writing Rules

* Rule Example::                An example explained.
* Rule Syntax::                 General syntax explained.
* Wildcards::                   Using wildcard characters such as `*'.
* Directory Search::            Searching other directories for source files.
* Phony Targets::               Using a target that is not a real file's name.
* Force Targets::               You can use a target without commands
                                  or prerequisites to mark other
                                  targets as phony.
* Empty Targets::               When only the date matters and the
                                  files are empty.
* Special Targets::             Targets with special built-in meanings.
* Multiple Targets::            When to make use of several targets in a rule.
* Multiple Rules::              How to use several rules with the same target.
* Static Pattern::              Static pattern rules apply to multiple targets
                                  and can vary the prerequisites according to
                                  the target name.
* Double-Colon::                How to use a special kind of rule to allow
                                  several independent rules for one target.
* Automatic Prerequisites::     How to automatically generate rules giving
                                 prerequisites from source files themselves.

Using Wildcard Characters in File Names

* Wildcard Examples::           Several examples
* Wildcard Pitfall::            Problems to avoid.
* Wildcard Function::           How to cause wildcard expansion where
                                  it does not normally take place.

Searching Directories for Prerequisites

* General Search::              Specifying a search path that applies
                                  to every prerequisite.
* Selective Search::            Specifying a search path
                                  for a specified class of names.
* Search Algorithm::            When and how search paths are applied.
* Commands/Search::             How to write shell commands that work together
                                  with search paths.
* Implicit/Search::             How search paths affect implicit rules.
* Libraries/Search::            Directory search for link libraries.

Static Pattern Rules

* Static Usage::                The syntax of static pattern rules.
* Static versus Implicit::      When are they better than implicit rules?

Writing the Commands in Rules

* Echoing::                     How to control when commands are echoed.
* Execution::                   How commands are executed.
* Parallel::                    How commands can be executed in parallel.
* Errors::                      What happens after a command execution error.
* Interrupts::                  What happens when a command is interrupted.
* Recursion::                   Invoking @code{make} from makefiles.
* Sequences::                   Defining canned sequences of commands.
* Empty Commands::              Defining useful, do-nothing commands.

Recursive Use of @code{make}

* MAKE Variable::               The special effects of using @samp{$(MAKE)}.
* Variables/Recursion::         How to communicate variables to a sub-@code{make}.
* Options/Recursion::           How to communicate options to a sub-@code{make}.
* -w Option::                   How the @samp{-w} or @samp{--print-directory} option
                                 helps debug use of recursive @code{make} commands.

How to Use Variables

* Reference::                   How to use the value of a variable.
* Flavors::                     Variables come in two flavors.
* Advanced::                    Advanced features for referencing a variable.
* Values::                      All the ways variables get their values.
* Setting::                     How to set a variable in the makefile.
* Appending::                   How to append more text to the old value
                                  of a variable.
* Override Directive::          How to set a variable in the makefile even if
                                  the user has set it with a command argument.
* Defining::                    An alternate way to set a variable
                                  to a verbatim string.
* Environment::                 Variable values can come from the environment.
* Automatic::                   Some special variables have predefined
                                  meanings for use with implicit rules.

Advanced Features for Reference to Variables

* Substitution Refs::           Referencing a variable with
                                  substitutions on the value.
* Computed Names::              Computing the name of the variable to refer to.

Conditional Parts of Makefiles

* Conditional Example::         Example of a conditional
* Conditional Syntax::          The syntax of conditionals.
* Testing Flags::               Conditionals that test flags.

Functions for Transforming Text

* Syntax of Functions::         How to write a function call.
* Text Functions::              General-purpose text manipulation functions.
* File Name Functions::         Functions for manipulating file names.
* Foreach Function::            Repeat some text with controlled variation.
* Call Function::               Expand a user-defined function.
* Origin Function::             Find where a variable got its value.
* Shell Function::              Substitute the output of a shell command.

How to Run @code{make}

* Makefile Arguments::          How to specify which makefile to use.
* Goals::                       How to use goal arguments to specify which
                                  parts of the makefile to use.
* Instead of Execution::        How to use mode flags to specify what
                                  kind of thing to do with the commands
                                  in the makefile other than simply
                                  execute them.
* Avoiding Compilation::        How to avoid recompiling certain files.
* Overriding::                  How to override a variable to specify
                                  an alternate compiler and other things.
* Testing::                     How to proceed past some errors, to
                                  test compilation.
* Options Summary::             Summary of Options

Using Implicit Rules

* Using Implicit::              How to use an existing implicit rule
                                  to get the commands for updating a file.
* Catalogue of Rules::          A list of built-in implicit rules.
* Implicit Variables::          How to change what predefined rules do.
* Chained Rules::               How to use a chain of implicit rules.
* Pattern Rules::               How to define new implicit rules.
* Last Resort::                 How to defining commands for rules
                                  which cannot find any.
* Suffix Rules::                The old-fashioned style of implicit rule.
* Implicit Rule Search::        The precise algorithm for applying
                                  implicit rules.

Defining and Redefining Pattern Rules

* Pattern Intro::               An introduction to pattern rules.
* Pattern Examples::            Examples of pattern rules.
* Automatic::                   How to use automatic variables in the
                                  commands of implicit rules.
* Pattern Match::               How patterns match.
* Match-Anything Rules::        Precautions you should take prior to
                                  defining rules that can match any
                                  target file whatever.
* Canceling Rules::             How to override or cancel built-in rules.

Using @code{make} to Update Archive Files

* Archive Members::             Archive members as targets.
* Archive Update::              The implicit rule for archive member targets.
* Archive Pitfalls::            Dangers to watch out for when using archives.
* Archive Suffix Rules::        You can write a special kind of suffix rule
                                  for updating archives.

Implicit Rule for Archive Member Targets

* Archive Symbols::             How to update archive symbol directories.
@end menu

@node Overview, Introduction, Top, Top
@comment  node-name,  next,  previous,  up
@chapter Overview of @code{make}

The @code{make} utility automatically determines which pieces of a large
program need to be recompiled, and issues commands to recompile them.
This manual describes GNU @code{make}, which was implemented by Richard
Stallman and Roland McGrath.  Development since Version 3.76 has been
handled by Paul D. Smith.

GNU @code{make} conforms to section 6.2 of @cite{IEEE Standard
1003.2-1992} (POSIX.2).
@cindex POSIX
@cindex IEEE Standard 1003.2
@cindex standards conformance

Our examples show C programs, since they are most common, but you can use
@code{make} with any programming language whose compiler can be run with a
shell command.  Indeed, @code{make} is not limited to programs.  You can
use it to describe any task where some files must be updated automatically
from others whenever the others change.

@menu
* Preparing::                   Preparing and Running Make
* Reading::                     On Reading this Text
* Bugs::                        Problems and Bugs
@end menu

@node Preparing, Reading,  , Overview
@ifinfo
@heading Preparing and Running Make
@end ifinfo

To prepare to use @code{make}, you must write a file called
the @dfn{makefile} that describes the relationships among files
in your program and provides commands for updating each file.
In a program, typically, the executable file is updated from object
files, which are in turn made by compiling source files.@refill

Once a suitable makefile exists, each time you change some source files,
this simple shell command:

@example
make
@end example

@noindent
suffices to perform all necessary recompilations.  The @code{make} program
uses the makefile data base and the last-modification times of the files to
decide which of the files need to be updated.  For each of those files, it
issues the commands recorded in the data base.

You can provide command line arguments to @code{make} to control which
files should be recompiled, or how.  @xref{Running, ,How to Run
@code{make}}.

@node Reading, Bugs, Preparing, Overview
@section How to Read This Manual

If you are new to @code{make}, or are looking for a general
introduction, read the first few sections of each chapter, skipping the
later sections.  In each chapter, the first few sections contain
introductory or general information and the later sections contain
specialized or technical information.
@ifinfo
The exception is the second chapter, @ref{Introduction, ,An
Introduction to Makefiles}, all of which is introductory.
@end ifinfo
@iftex
The exception is @ref{Introduction, ,An Introduction to Makefiles},
all of which is introductory.
@end iftex

If you are familiar with other @code{make} programs, see @ref{Features,
,Features of GNU @code{make}}, which lists the enhancements GNU
@code{make} has, and @ref{Missing, ,Incompatibilities and Missing
Features}, which explains the few things GNU @code{make} lacks that
others have.

For a quick summary, see @ref{Options Summary}, @ref{Quick Reference},
and @ref{Special Targets}.

@node Bugs,  , Reading, Overview
@section Problems and Bugs
@cindex reporting bugs
@cindex bugs, reporting
@cindex problems and bugs, reporting

If you have problems with GNU @code{make} or think you've found a bug,
please report it to the developers; we cannot promise to do anything but
we might well want to fix it.

Before reporting a bug, make sure you've actually found a real bug.
Carefully reread the documentation and see if it really says you can do
what you're trying to do.  If it's not clear whether you should be able
to do something or not, report that too; it's a bug in the
documentation!

Before reporting a bug or trying to fix it yourself, try to isolate it
to the smallest possible makefile that reproduces the problem.  Then
send us the makefile and the exact results @code{make} gave you.  Also
say what you expected to occur; this will help us decide whether the
problem was really in the documentation.

Once you've got a precise problem, please send electronic mail to:

@example
    bug-make@@gnu.org
@end example

@noindent
Please include the version number of @code{make} you are using.  You can
get this information with the command @samp{make --version}.
Be sure also to include the type of machine and operating system you are
using.  If possible, include the contents of the file @file{config.h}
that is generated by the configuration process.

@node Introduction, Makefiles, Overview, Top
@comment  node-name,  next,  previous,  up
@chapter An Introduction to Makefiles

You need a file called a @dfn{makefile} to tell @code{make} what to do.
Most often, the makefile tells @code{make} how to compile and link a
program.
@cindex makefile

In this chapter, we will discuss a simple makefile that describes how to
compile and link a text editor which consists of eight C source files
and three header files.  The makefile can also tell @code{make} how to
run miscellaneous commands when explicitly asked (for example, to remove
certain files as a clean-up operation).  To see a more complex example
of a makefile, see @ref{Complex Makefile}.

When @code{make} recompiles the editor, each changed C source file
must be recompiled.  If a header file has changed, each C source file
that includes the header file must be recompiled to be safe.  Each
compilation produces an object file corresponding to the source file.
Finally, if any source file has been recompiled, all the object files,
whether newly made or saved from previous compilations, must be linked
together to produce the new executable editor.
@cindex recompilation
@cindex editor

@menu
* Rule Introduction::           What a rule looks like.
* Simple Makefile::             A Simple Makefile
* How Make Works::              How @code{make} Processes This Makefile
* Variables Simplify::          Variables Make Makefiles Simpler
* make Deduces::                Letting @code{make} Deduce the Commands
* Combine By Prerequisite::     Another Style of Makefile
* Cleanup::                     Rules for Cleaning the Directory
@end menu

@node Rule Introduction, Simple Makefile,  , Introduction
@comment  node-name,  next,  previous,  up
@section What a Rule Looks Like
@cindex rule, introduction to
@cindex makefile rule parts
@cindex parts of makefile rule

A simple makefile consists of ``rules'' with the following shape:

@cindex targets, introduction to
@cindex prerequisites, introduction to
@cindex commands, introduction to
@example
@group
@var{target} @dots{} : @var{prerequisites} @dots{}
        @var{command}
        @dots{}
        @dots{}
@end group
@end example

A @dfn{target} is usually the name of a file that is generated by a
program; examples of targets are executable or object files.  A target
can also be the name of an action to carry out, such as @samp{clean}
(@pxref{Phony Targets}).

A @dfn{prerequisite} is a file that is used as input to create the
target.  A target often depends on several files.

@cindex tabs in rules
A @dfn{command} is an action that @code{make} carries out.
A rule may have more than one command, each on its own line.
@strong{Please note:} you need to put a tab character at the beginning of
every command line!  This is an obscurity that catches the unwary.

Usually a command is in a rule with prerequisites and serves to create a
target file if any of the prerequisites change.  However, the rule that
specifies commands for the target need not have prerequisites.  For
example, the rule containing the delete command associated with the
target @samp{clean} does not have prerequisites.

A @dfn{rule}, then, explains how and when to remake certain files
which are the targets of the particular rule.  @code{make} carries out
the commands on the prerequisites to create or update the target.  A
rule can also explain how and when to carry out an action.
@xref{Rules, , Writing Rules}.

A makefile may contain other text besides rules, but a simple makefile
need only contain rules.  Rules may look somewhat more complicated
than shown in this template, but all fit the pattern more or less.

@node Simple Makefile, How Make Works, Rule Introduction, Introduction
@section A Simple Makefile
@cindex simple makefile
@cindex makefile, simple

Here is a straightforward makefile that describes the way an
executable file called @code{edit} depends on eight object files
which, in turn, depend on eight C source and three header files.

In this example, all the C files include @file{defs.h}, but only those
defining editing commands include @file{command.h}, and only low
level files that change the editor buffer include @file{buffer.h}.

@example
@group
edit : main.o kbd.o command.o display.o \
       insert.o search.o files.o utils.o
        cc -o edit main.o kbd.o command.o display.o \
                   insert.o search.o files.o utils.o

main.o : main.c defs.h
        cc -c main.c
kbd.o : kbd.c defs.h command.h
        cc -c kbd.c
command.o : command.c defs.h command.h
        cc -c command.c
display.o : display.c defs.h buffer.h
        cc -c display.c
insert.o : insert.c defs.h buffer.h
        cc -c insert.c
search.o : search.c defs.h buffer.h
        cc -c search.c
files.o : files.c defs.h buffer.h command.h
        cc -c files.c
utils.o : utils.c defs.h
        cc -c utils.c
clean :
        rm edit main.o kbd.o command.o display.o \
           insert.o search.o files.o utils.o
@end group
@end example

@noindent
We split each long line into two lines using backslash-newline; this is
like using one long line, but is easier to read.
@cindex continuation lines
@cindex @code{\} (backslash), for continuation lines
@cindex backslash (@code{\}), for continuation lines
@cindex quoting newline, in makefile
@cindex newline, quoting, in makefile

To use this makefile to create the executable file called @file{edit},
type:

@example
make
@end example

To use this makefile to delete the executable file and all the object
files from the directory, type:

@example
make clean
@end example

In the example makefile, the targets include the executable file
@samp{edit}, and the object files @samp{main.o} and @samp{kbd.o}.  The
prerequisites are files such as @samp{main.c} and @samp{defs.h}.
In fact, each @samp{.o} file is both a target and a prerequisite.
Commands include @w{@samp{cc -c main.c}} and @w{@samp{cc -c kbd.c}}.

When a target is a file, it needs to be recompiled or relinked if any
of its prerequisites change.  In addition, any prerequisites that are
themselves automatically generated should be updated first.  In this
example, @file{edit} depends on each of the eight object files; the
object file @file{main.o} depends on the source file @file{main.c} and
on the header file @file{defs.h}.

A shell command follows each line that contains a target and
prerequisites.  These shell commands say how to update the target file.
A tab character must come at the beginning of every command line to
distinguish commands lines from other lines in the makefile.  (Bear in
mind that @code{make} does not know anything about how the commands
work.  It is up to you to supply commands that will update the target
file properly.  All @code{make} does is execute the commands in the rule
you have specified when the target file needs to be updated.)
@cindex shell command

The target @samp{clean} is not a file, but merely the name of an
action.  Since you
normally
do not want to carry out the actions in this rule, @samp{clean} is not a prerequisite of any other rule.
Consequently, @code{make} never does anything with it unless you tell
it specifically.  Note that this rule not only is not a prerequisite, it
also does not have any prerequisites, so the only purpose of the rule
is to run the specified commands.  Targets that do not refer to files
but are just actions are called @dfn{phony targets}.  @xref{Phony
Targets}, for information about this kind of target.  @xref{Errors, ,
Errors in Commands}, to see how to cause @code{make} to ignore errors
from @code{rm} or any other command.
@cindex @code{clean} target
@cindex @code{rm} (shell command)

@node How Make Works, Variables Simplify, Simple Makefile, Introduction
@comment  node-name,  next,  previous,  up
@section How @code{make} Processes a Makefile
@cindex processing a makefile
@cindex makefile, how @code{make} processes

By default, @code{make} starts with the first target (not targets whose
names start with @samp{.}).  This is called the @dfn{default goal}.
(@dfn{Goals} are the targets that @code{make} strives ultimately to
update.  @xref{Goals, , Arguments to Specify the Goals}.)
@cindex default goal
@cindex goal, default
@cindex goal

In the simple example of the previous section, the default goal is to
update the executable program @file{edit}; therefore, we put that rule
first.

Thus, when you give the command:

@example
make
@end example

@noindent
@code{make} reads the makefile in the current directory and begins by
processing the first rule.  In the example, this rule is for relinking
@file{edit}; but before @code{make} can fully process this rule, it
must process the rules for the files that @file{edit} depends on,
which in this case are the object files.  Each of these files is
processed according to its own rule.  These rules say to update each
@samp{.o} file by compiling its source file.  The recompilation must
be done if the source file, or any of the header files named as
prerequisites, is more recent than the object file, or if the object
file does not exist.

The other rules are processed because their targets appear as
prerequisites of the goal.  If some other rule is not depended on by the
goal (or anything it depends on, etc.), that rule is not processed,
unless you tell @code{make} to do so (with a command such as
@w{@code{make clean}}).

Before recompiling an object file, @code{make} considers updating its
prerequisites, the source file and header files.  This makefile does not
specify anything to be done for them---the @samp{.c} and @samp{.h} files
are not the targets of any rules---so @code{make} does nothing for these
files.  But @code{make} would update automatically generated C programs,
such as those made by Bison or Yacc, by their own rules at this time.

After recompiling whichever object files need it, @code{make} decides
whether to relink @file{edit}.  This must be done if the file
@file{edit} does not exist, or if any of the object files are newer than
it.  If an object file was just recompiled, it is now newer than
@file{edit}, so @file{edit} is relinked.
@cindex relinking

Thus, if we change the file @file{insert.c} and run @code{make},
@code{make} will compile that file to update @file{insert.o}, and then
link @file{edit}.  If we change the file @file{command.h} and run
@code{make}, @code{make} will recompile the object files @file{kbd.o},
@file{command.o} and @file{files.o} and then link the file @file{edit}.

@node Variables Simplify, make Deduces, How Make Works, Introduction
@section Variables Make Makefiles Simpler
@cindex variables
@cindex simplifying with variables

In our example, we had to list all the object files twice in the rule for
@file{edit} (repeated here):

@example
@group
edit : main.o kbd.o command.o display.o \
              insert.o search.o files.o utils.o
        cc -o edit main.o kbd.o command.o display.o \
                   insert.o search.o files.o utils.o
@end group
@end example

@cindex @code{objects}
Such duplication is error-prone; if a new object file is added to the
system, we might add it to one list and forget the other.  We can eliminate
the risk and simplify the makefile by using a variable.  @dfn{Variables}
allow a text string to be defined once and substituted in multiple places
later (@pxref{Using Variables, ,How to Use Variables}).

@cindex @code{OBJECTS}
@cindex @code{objs}
@cindex @code{OBJS}
@cindex @code{obj}
@cindex @code{OBJ}
It is standard practice for every makefile to have a variable named
@code{objects}, @code{OBJECTS}, @code{objs}, @code{OBJS}, @code{obj},
or @code{OBJ} which is a list of all object file names.  We would
define such a variable @code{objects} with a line like this in the
makefile:@refill

@example
@group
objects = main.o kbd.o command.o display.o \
          insert.o search.o files.o utils.o
@end group
@end example

@noindent
Then, each place we want to put a list of the object file names, we can
substitute the variable's value by writing @samp{$(objects)}
(@pxref{Using Variables, ,How to Use Variables}).

Here is how the complete simple makefile looks when you use a variable
for the object files:

@example
@group
objects = main.o kbd.o command.o display.o \
          insert.o search.o files.o utils.o

edit : $(objects)
        cc -o edit $(objects)
main.o : main.c defs.h
        cc -c main.c
kbd.o : kbd.c defs.h command.h
        cc -c kbd.c
command.o : command.c defs.h command.h
        cc -c command.c
display.o : display.c defs.h buffer.h
        cc -c display.c
insert.o : insert.c defs.h buffer.h
        cc -c insert.c
search.o : search.c defs.h buffer.h
        cc -c search.c
files.o : files.c defs.h buffer.h command.h
        cc -c files.c
utils.o : utils.c defs.h
        cc -c utils.c
clean :
        rm edit $(objects)
@end group
@end example

@node make Deduces, Combine By Prerequisite, Variables Simplify, Introduction
@section Letting @code{make} Deduce the Commands
@cindex deducing commands (implicit rules)
@cindex implicit rule, introduction to
@cindex rule, implicit, introduction to

It is not necessary to spell out the commands for compiling the individual
C source files, because @code{make} can figure them out: it has an
@dfn{implicit rule} for updating a @samp{.o} file from a correspondingly
named @samp{.c} file using a @samp{cc -c} command.  For example, it will
use the command @samp{cc -c main.c -o main.o} to compile @file{main.c} into
@file{main.o}.  We can therefore omit the commands from the rules for the
object files.  @xref{Implicit Rules, ,Using Implicit Rules}.@refill

When a @samp{.c} file is used automatically in this way, it is also
automatically added to the list of prerequisites.  We can therefore omit
the @samp{.c} files from the prerequisites, provided we omit the commands.

Here is the entire example, with both of these changes, and a variable
@code{objects} as suggested above:

@example
@group
objects = main.o kbd.o command.o display.o \
          insert.o search.o files.o utils.o

edit : $(objects)
        cc -o edit $(objects)

main.o : defs.h
kbd.o : defs.h command.h
command.o : defs.h command.h
display.o : defs.h buffer.h
insert.o : defs.h buffer.h
search.o : defs.h buffer.h
files.o : defs.h buffer.h command.h
utils.o : defs.h

.PHONY : clean
clean :
        -rm edit $(objects)
@end group
@end example

@noindent
This is how we would write the makefile in actual practice.  (The
complications associated with @samp{clean} are described elsewhere.
See @ref{Phony Targets}, and @ref{Errors, ,Errors in Commands}.)

Because implicit rules are so convenient, they are important.  You
will see them used frequently.@refill

@node Combine By Prerequisite, Cleanup, make Deduces, Introduction
@section Another Style of Makefile
@cindex combining rules by prerequisite

When the objects of a makefile are created only by implicit rules, an
alternative style of makefile is possible.  In this style of makefile,
you group entries by their prerequisites instead of by their targets.
Here is what one looks like:

@example
@group
objects = main.o kbd.o command.o display.o \
          insert.o search.o files.o utils.o

edit : $(objects)
        cc -o edit $(objects)

$(objects) : defs.h
kbd.o command.o files.o : command.h
display.o insert.o search.o files.o : buffer.h
@end group
@end example

@noindent
Here @file{defs.h} is given as a prerequisite of all the object files;
@file{command.h} and @file{buffer.h} are prerequisites of the specific
object files listed for them.

Whether this is better is a matter of taste: it is more compact, but some
people dislike it because they find it clearer to put all the information
about each target in one place.

@node Cleanup,  , Combine By Prerequisite, Introduction
@section Rules for Cleaning the Directory
@cindex cleaning up
@cindex removing, to clean up

Compiling a program is not the only thing you might want to write rules
for.  Makefiles commonly tell how to do a few other things besides
compiling a program: for example, how to delete all the object files
and executables so that the directory is @samp{clean}.

@cindex @code{clean} target
Here is how we
could write a @code{make} rule for cleaning our example editor:

@example
@group
clean:
        rm edit $(objects)
@end group
@end example

In practice, we might want to write the rule in a somewhat more
complicated manner to handle unanticipated situations.  We would do this:

@example
@group
.PHONY : clean
clean :
        -rm edit $(objects)
@end group
@end example

@noindent
This prevents @code{make} from getting confused by an actual file
called @file{clean} and causes it to continue in spite of errors from
@code{rm}.  (See @ref{Phony Targets}, and @ref{Errors, ,Errors in
Commands}.)

@noindent
A rule such as this should not be placed at the beginning of the
makefile, because we do not want it to run by default!  Thus, in the
example makefile, we want the rule for @code{edit}, which recompiles
the editor, to remain the default goal.

Since @code{clean} is not a prerequisite of @code{edit}, this rule will not
run at all if we give the command @samp{make} with no arguments.  In
order to make the rule run, we have to type @samp{make clean}.
@xref{Running, ,How to Run @code{make}}.

@node Makefiles, Rules, Introduction, Top
@chapter Writing Makefiles

@cindex makefile, how to write
The information that tells @code{make} how to recompile a system comes from
reading a data base called the @dfn{makefile}.

@menu
* Makefile Contents::           What makefiles contain.
* Makefile Names::              How to name your makefile.
* Include::                     How one makefile can use another makefile.
* MAKEFILES Variable::          The environment can specify extra makefiles.
* Remaking Makefiles::          How makefiles get remade.
* Overriding Makefiles::        How to override part of one makefile
                                 with another makefile.
* Reading Makefiles::           How makefiles are parsed.
@end menu

@node Makefile Contents, Makefile Names,  , Makefiles
@section What Makefiles Contain

Makefiles contain five kinds of things: @dfn{explicit rules},
@dfn{implicit rules}, @dfn{variable definitions}, @dfn{directives},
and @dfn{comments}.  Rules, variables, and directives are described at
length in later chapters.@refill

@itemize @bullet
@cindex rule, explicit, definition of
@cindex explicit rule, definition of
@item
An @dfn{explicit rule} says when and how to remake one or more files,
called the rule's targets.  It lists the other files that the targets
depend on, call the @dfn{prerequisites} of the target, and may also give
commands to use to create or update the targets.  @xref{Rules, ,Writing
Rules}.

@cindex rule, implicit, definition of
@cindex implicit rule, definition of
@item
An @dfn{implicit rule} says when and how to remake a class of files
based on their names.  It describes how a target may depend on a file
with a name similar to the target and gives commands to create or
update such a target.  @xref{Implicit Rules, ,Using Implicit Rules}.

@cindex variable definition
@item
A @dfn{variable definition} is a line that specifies a text string
value for a variable that can be substituted into the text later.  The
simple makefile example shows a variable definition for @code{objects}
as a list of all object files (@pxref{Variables Simplify, , Variables
Make Makefiles Simpler}).

@cindex directive
@item
A @dfn{directive} is a command for @code{make} to do something special while
reading the makefile.  These include:

@itemize @bullet
@item
Reading another makefile (@pxref{Include, ,Including Other Makefiles}).

@item
Deciding (based on the values of variables) whether to use or
ignore a part of the makefile (@pxref{Conditionals, ,Conditional Parts of Makefiles}).

@item
Defining a variable from a verbatim string containing multiple lines
(@pxref{Defining, ,Defining Variables Verbatim}).
@end itemize

@cindex comments, in makefile
@cindex @code{#} (comments), in makefile
@item
@samp{#} in a line of a makefile starts a @dfn{comment}.  It and the rest of
the line are ignored, except that a trailing backslash not escaped by
another backslash will continue the comment across multiple lines.
Comments may appear on any of the lines in the makefile, except within a
@code{define} directive, and perhaps within commands (where the shell
decides what is a comment).  A line containing just a comment (with
perhaps spaces before it) is effectively blank, and is ignored.@refill
@end itemize

@node Makefile Names, Include, Makefile Contents, Makefiles
@section What Name to Give Your Makefile
@cindex makefile name
@cindex name of makefile
@cindex default makefile name
@cindex file name of makefile

@c following paragraph rewritten to avoid overfull hbox
By default, when @code{make} looks for the makefile, it tries the
following names, in order: @file{GNUmakefile}, @file{makefile}
and @file{Makefile}.@refill
@findex Makefile
@findex GNUmakefile
@findex makefile

@cindex @code{README}
Normally you should call your makefile either @file{makefile} or
@file{Makefile}.  (We recommend @file{Makefile} because it appears
prominently near the beginning of a directory listing, right near other
important files such as @file{README}.)  The first name checked,
@file{GNUmakefile}, is not recommended for most makefiles.  You should
use this name if you have a makefile that is specific to GNU
@code{make}, and will not be understood by other versions of
@code{make}.  Other @code{make} programs look for @file{makefile} and
@file{Makefile}, but not @file{GNUmakefile}.

If @code{make} finds none of these names, it does not use any makefile.
Then you must specify a goal with a command argument, and @code{make}
will attempt to figure out how to remake it using only its built-in
implicit rules.  @xref{Implicit Rules, ,Using Implicit Rules}.

@cindex @code{-f}
@cindex @code{--file}
@cindex @code{--makefile}
If you want to use a nonstandard name for your makefile, you can specify
the makefile name with the @samp{-f} or @samp{--file} option.  The
arguments @w{@samp{-f @var{name}}} or @w{@samp{--file=@var{name}}} tell
@code{make} to read the file @var{name} as the makefile.  If you use
more than one @samp{-f} or @samp{--file} option, you can specify several
makefiles.  All the makefiles are effectively concatenated in the order
specified.  The default makefile names @file{GNUmakefile},
@file{makefile} and @file{Makefile} are not checked automatically if you
specify @samp{-f} or @samp{--file}.@refill
@cindex specifying makefile name
@cindex makefile name, how to specify
@cindex name of makefile, how to specify
@cindex file name of makefile, how to specify

@node Include, MAKEFILES Variable, Makefile Names, Makefiles
@section Including Other Makefiles
@cindex including other makefiles
@cindex makefile, including

@findex include
The @code{include} directive tells @code{make} to suspend reading the
current makefile and read one or more other makefiles before continuing.
The directive is a line in the makefile that looks like this:

@example
include @var{filenames}@dots{}
@end example

@noindent
@var{filenames} can contain shell file name patterns.
@cindex shell file name pattern (in @code{include})
@cindex shell wildcards (in @code{include})
@cindex wildcard, in @code{include}

Extra spaces are allowed and ignored at the beginning of the line, but
a tab is not allowed.  (If the line begins with a tab, it will be
considered a command line.)  Whitespace is required between
@code{include} and the file names, and between file names; extra
whitespace is ignored there and at the end of the directive.  A
comment starting with @samp{#} is allowed at the end of the line.  If
the file names contain any variable or function references, they are
expanded.  @xref{Using Variables, ,How to Use Variables}.

For example, if you have three @file{.mk} files, @file{a.mk},
@file{b.mk}, and @file{c.mk}, and @code{$(bar)} expands to
@code{bish bash}, then the following expression

@example
include foo *.mk $(bar)
@end example

is equivalent to

@example
include foo a.mk b.mk c.mk bish bash
@end example

When @code{make} processes an @code{include} directive, it suspends
reading of the containing makefile and reads from each listed file in
turn.  When that is finished, @code{make} resumes reading the
makefile in which the directive appears.

One occasion for using @code{include} directives is when several programs,
handled by individual makefiles in various directories, need to use a
common set of variable definitions
(@pxref{Setting, ,Setting Variables}) or pattern rules
(@pxref{Pattern Rules, ,Defining and Redefining Pattern Rules}).

Another such occasion is when you want to generate prerequisites from
source files automatically; the prerequisites can be put in a file that
is included by the main makefile.  This practice is generally cleaner
than that of somehow appending the prerequisites to the end of the main
makefile as has been traditionally done with other versions of
@code{make}.  @xref{Automatic Prerequisites}.
@cindex prerequisites, automatic generation
@cindex automatic generation of prerequisites
@cindex generating prerequisites automatically

@cindex @code{-I}
@cindex @code{--include-dir}
@cindex included makefiles, default directries
@cindex default directries for included makefiles
@findex /usr/gnu/include
@findex /usr/local/include
@findex /usr/include
If the specified name does not start with a slash, and the file is not
found in the current directory, several other directories are searched.
First, any directories you have specified with the @samp{-I} or
@samp{--include-dir} option are searched
(@pxref{Options Summary, ,Summary of Options}).
Then the following directories (if they exist)
are searched, in this order:
@file{@var{prefix}/include} (normally @file{/usr/local/include}
@footnote{GNU Make compiled for MS-DOS and MS-Windows behaves as if
@var{prefix} has been defined to be the root of the DJGPP tree
hierarchy.})
@file{/usr/gnu/include},
@file{/usr/local/include}, @file{/usr/include}.

If an included makefile cannot be found in any of these directories, a
warning message is generated, but it is not an immediately fatal error;
processing of the makefile containing the @code{include} continues.
Once it has finished reading makefiles, @code{make} will try to remake
any that are out of date or don't exist.
@xref{Remaking Makefiles, ,How Makefiles Are Remade}.
Only after it has tried to find a way to remake a makefile and failed,
will @code{make} diagnose the missing makefile as a fatal error.

If you want @code{make} to simply ignore a makefile which does not exist
and cannot be remade, with no error message, use the @w{@code{-include}}
directive instead of @code{include}, like this:

@example
-include @var{filenames}@dots{}
@end example

This is acts like @code{include} in every way except that there is no
error (not even a warning) if any of the @var{filenames} do not exist.
For compatibility with some other @code{make} implementations,
@code{sinclude} is another name for @w{@code{-include}}.

@node MAKEFILES Variable, Remaking Makefiles, Include, Makefiles
@section The Variable @code{MAKEFILES}
@cindex makefile, and @code{MAKEFILES} variable
@cindex including (@code{MAKEFILES} variable)

@vindex MAKEFILES
If the environment variable @code{MAKEFILES} is defined, @code{make}
considers its value as a list of names (separated by whitespace) of
additional makefiles to be read before the others.  This works much like
the @code{include} directive: various directories are searched for those
files (@pxref{Include, ,Including Other Makefiles}).  In addition, the
default goal is never taken from one of these makefiles and it is not an
error if the files listed in @code{MAKEFILES} are not found.@refill

@cindex recursion, and @code{MAKEFILES} variable
The main use of @code{MAKEFILES} is in communication between recursive
invocations of @code{make} (@pxref{Recursion, ,Recursive Use of
@code{make}}).  It usually is not desirable to set the environment
variable before a top-level invocation of @code{make}, because it is
usually better not to mess with a makefile from outside.  However, if
you are running @code{make} without a specific makefile, a makefile in
@code{MAKEFILES} can do useful things to help the built-in implicit
rules work better, such as defining search paths (@pxref{Directory Search}).

Some users are tempted to set @code{MAKEFILES} in the environment
automatically on login, and program makefiles to expect this to be done.
This is a very bad idea, because such makefiles will fail to work if run by
anyone else.  It is much better to write explicit @code{include} directives
in the makefiles.  @xref{Include, , Including Other Makefiles}.

@node Remaking Makefiles, Overriding Makefiles, MAKEFILES Variable, Makefiles
@section How Makefiles Are Remade

@cindex updating makefiles
@cindex remaking makefiles
@cindex makefile, remaking of
Sometimes makefiles can be remade from other files, such as RCS or SCCS
files.  If a makefile can be remade from other files, you probably want
@code{make} to get an up-to-date version of the makefile to read in.

To this end, after reading in all makefiles, @code{make} will consider
each as a goal target and attempt to update it.  If a makefile has a
rule which says how to update it (found either in that very makefile or
in another one) or if an implicit rule applies to it (@pxref{Implicit
Rules, ,Using Implicit Rules}), it will be updated if necessary.  After
all makefiles have been checked, if any have actually been changed,
@code{make} starts with a clean slate and reads all the makefiles over
again.  (It will also attempt to update each of them over again, but
normally this will not change them again, since they are already up to
date.)@refill

If you know that one or more of your makefiles cannot be remade and you
want to keep @code{make} from performing an implicit rule search on
them, perhaps for efficiency reasons, you can use any normal method of
preventing implicit rule lookup to do so.  For example, you can write an
explicit rule with the makefile as the target, and an empty command
string (@pxref{Empty Commands, ,Using Empty Commands}).

If the makefiles specify a double-colon rule to remake a file with
commands but no prerequisites, that file will always be remade
(@pxref{Double-Colon}).  In the case of makefiles, a makefile that has a
double-colon rule with commands but no prerequisites will be remade every
time @code{make} is run, and then again after @code{make} starts over
and reads the makefiles in again.  This would cause an infinite loop:
@code{make} would constantly remake the makefile, and never do anything
else.  So, to avoid this, @code{make} will @strong{not} attempt to
remake makefiles which are specified as targets of a double-colon rule
with commands but no prerequisites.@refill

If you do not specify any makefiles to be read with @samp{-f} or
@samp{--file} options, @code{make} will try the default makefile names;
@pxref{Makefile Names, ,What Name to Give Your Makefile}.  Unlike
makefiles explicitly requested with @samp{-f} or @samp{--file} options,
@code{make} is not certain that these makefiles should exist.  However,
if a default makefile does not exist but can be created by running
@code{make} rules, you probably want the rules to be run so that the
makefile can be used.

Therefore, if none of the default makefiles exists, @code{make} will try
to make each of them in the same order in which they are searched for
(@pxref{Makefile Names, ,What Name to Give Your Makefile})
until it succeeds in making one, or it runs out of names to try.  Note
that it is not an error if @code{make} cannot find or make any makefile;
a makefile is not always necessary.@refill

When you use the @samp{-t} or @samp{--touch} option
(@pxref{Instead of Execution, ,Instead of Executing the Commands}),
you would not want to use an out-of-date makefile to decide which
targets to touch.  So the @samp{-t} option has no effect on updating
makefiles; they are really updated even if @samp{-t} is specified.
Likewise, @samp{-q} (or @samp{--question}) and @samp{-n} (or
@samp{--just-print}) do not prevent updating of makefiles, because an
out-of-date makefile would result in the wrong output for other targets.
Thus, @samp{make -f mfile -n foo} will update @file{mfile}, read it in,
and then print the commands to update @file{foo} and its prerequisites
without running them.  The commands printed for @file{foo} will be those
specified in the updated contents of @file{mfile}.

However, on occasion you might actually wish to prevent updating of even
the makefiles.  You can do this by specifying the makefiles as goals in
the command line as well as specifying them as makefiles.  When the
makefile name is specified explicitly as a goal, the options @samp{-t}
and so on do apply to them.

Thus, @samp{make -f mfile -n mfile foo} would read the makefile
@file{mfile}, print the commands needed to update it without actually
running them, and then print the commands needed to update @file{foo}
without running them.  The commands for @file{foo} will be those
specified by the existing contents of @file{mfile}.

@node Overriding Makefiles, Reading Makefiles, Remaking Makefiles, Makefiles
@section Overriding Part of Another Makefile

@cindex overriding makefiles
@cindex makefile, overriding
Sometimes it is useful to have a makefile that is mostly just like
another makefile.  You can often use the @samp{include} directive to
include one in the other, and add more targets or variable definitions.
However, if the two makefiles give different commands for the same
target, @code{make} will not let you just do this.  But there is another way.

@cindex match-anything rule, used to override
In the containing makefile (the one that wants to include the other),
you can use a match-anything pattern rule to say that to remake any
target that cannot be made from the information in the containing
makefile, @code{make} should look in another makefile.
@xref{Pattern Rules}, for more information on pattern rules.

For example, if you have a makefile called @file{Makefile} that says how
to make the target @samp{foo} (and other targets), you can write a
makefile called @file{GNUmakefile} that contains:

@example
foo:
        frobnicate > foo

%: force
        @@$(MAKE) -f Makefile $@@
force: ;
@end example

If you say @samp{make foo}, @code{make} will find @file{GNUmakefile},
read it, and see that to make @file{foo}, it needs to run the command
@samp{frobnicate > foo}.  If you say @samp{make bar}, @code{make} will
find no way to make @file{bar} in @file{GNUmakefile}, so it will use the
commands from the pattern rule: @samp{make -f Makefile bar}.  If
@file{Makefile} provides a rule for updating @file{bar}, @code{make}
will apply the rule.  And likewise for any other target that
@file{GNUmakefile} does not say how to make.

The way this works is that the pattern rule has a pattern of just
@samp{%}, so it matches any target whatever.  The rule specifies a
prerequisite @file{force}, to guarantee that the commands will be run even
if the target file already exists.  We give @file{force} target empty
commands to prevent @code{make} from searching for an implicit rule to
build it---otherwise it would apply the same match-anything rule to
@file{force} itself and create a prerequisite loop!

@node Reading Makefiles,  , Overriding Makefiles, Makefiles
@section How @code{make} Reads a Makefile
@cindex reading makefiles
@cindex makefile, parsing

GNU @code{make} does its work in two distinct phases.  During the first
phase it reads all the makefiles, included makefiles, etc. and
internalizes all the variables and their values, implicit and explicit
rules, and constructs a dependency graph of all the targets and their
prerequisites.  During the second phase, @code{make} uses these internal
structures to determine what targets will need to be rebuilt and to
invoke the rules necessary to do so.

It's important to understand this two-phase approach because it has a
direct impact on how variable and function expansion happens; this is
often a source of some confusion when writing makefiles.  Here we will
present a summary of the phases in which expansion happens for different
constructs within the makefile.  We say that expansion is
@dfn{immediate} if it happens during the first phase: in this case
@code{make} will expand any variables or functions in that section of a
construct as the makefile is parsed.  We say that expansion is
@dfn{deferred} if expansion is not performed immediately.  Expansion of
deferred construct is not performed until either the construct appears
later in an immediate context, or until the second phase.

You may not be familiar with some of these constructs yet.  You can
reference this section as you become familiar with them, in later
chapters.

@subheading Variable Assignment
@cindex +=, expansion
@cindex =, expansion
@cindex ?=, expansion
@cindex +=, expansion
@cindex define, expansion

Variable definitions are parsed as follows:

@example
@var{immediate} = @var{deferred}
@var{immediate} ?= @var{deferred}
@var{immediate} := @var{immediate}
@var{immediate} += @var{deferred} or @var{immediate}

define @var{immediate}
  @var{deferred}
endef
@end example

For the append operator, @samp{+=}, the right-hand side is considered
immediate if the variable was previously set as a simple variable
(@samp{:=}), and deferred otherwise.

@subheading Conditional Syntax
@cindex ifdef, expansion
@cindex ifeq, expansion
@cindex ifndef, expansion
@cindex ifneq, expansion

All instances of conditional syntax are parsed immediately, in their
entirety; this includes the @code{ifdef}, @code{ifeq}, @code{ifndef},
and @code{ifneq} forms.

@subheading Rule Definition
@cindex target, expansion
@cindex prerequisite, expansion
@cindex implicit rule, expansion
@cindex pattern rule, expansion
@cindex explicit rule, expansion

A rule is always expanded the same way, regardless of the form:

@example
@var{immediate} : @var{immediate} ; @var{deferred}
	@var{deferred}
@end example

That is, the target and prerequisite sections are expanded immediately,
and the commands used to construct the target are always deferred.  This
general rule is true for explicit rules, pattern rules, suffix rules,
static pattern rules, and simple prerequisite definitions.

@node Rules, Commands, Makefiles, Top
@chapter Writing Rules
@cindex writing rules
@cindex rule, how to write
@cindex target
@cindex prerequisite

A @dfn{rule} appears in the makefile and says when and how to remake
certain files, called the rule's @dfn{targets} (most often only one per rule).
It lists the other files that are the @dfn{prerequisites} of the target, and
@dfn{commands} to use to create or update the target.

@cindex default goal
@cindex goal, default
The order of rules is not significant, except for determining the
@dfn{default goal}: the target for @code{make} to consider, if you do
not otherwise specify one.  The default goal is the target of the first
rule in the first makefile.  If the first rule has multiple targets,
only the first target is taken as the default.  There are two
exceptions: a target starting with a period is not a default unless it
contains one or more slashes, @samp{/}, as well; and, a target that
defines a pattern rule has no effect on the default goal.
(@xref{Pattern Rules, ,Defining and Redefining Pattern Rules}.)

Therefore, we usually write the makefile so that the first rule is the
one for compiling the entire program or all the programs described by
the makefile (often with a target called @samp{all}).
@xref{Goals, ,Arguments to Specify the Goals}.

@menu
* Rule Example::                An example explained.
* Rule Syntax::                 General syntax explained.
* Wildcards::                   Using wildcard characters such as `*'.
* Directory Search::            Searching other directories for source files.
* Phony Targets::               Using a target that is not a real file's name.
* Force Targets::               You can use a target without commands
                                  or prerequisites to mark other
                                  targets as phony.
* Empty Targets::               When only the date matters and the
                                  files are empty.
* Special Targets::             Targets with special built-in meanings.
* Multiple Targets::            When to make use of several targets in a rule.
* Multiple Rules::              How to use several rules with the same target.
* Static Pattern::              Static pattern rules apply to multiple targets
                                  and can vary the prerequisites according to
                                  the target name.
* Double-Colon::                How to use a special kind of rule to allow
                                  several independent rules for one target.
* Automatic Prerequisites::     How to automatically generate rules giving
                                  prerequisites from source files themselves.
@end menu

@ifinfo
@node Rule Example, Rule Syntax,  , Rules
@section Rule Example

Here is an example of a rule:

@example
foo.o : foo.c defs.h       # module for twiddling the frobs
        cc -c -g foo.c
@end example

Its target is @file{foo.o} and its prerequisites are @file{foo.c} and
@file{defs.h}.  It has one command, which is @samp{cc -c -g foo.c}.
The command line starts with a tab to identify it as a command.

This rule says two things:

@itemize @bullet
@item
How to decide whether @file{foo.o} is out of date: it is out of date
if it does not exist, or if either @file{foo.c} or @file{defs.h} is
more recent than it.

@item
How to update the file @file{foo.o}: by running @code{cc} as stated.
The command does not explicitly mention @file{defs.h}, but we presume
that @file{foo.c} includes it, and that that is why @file{defs.h} was
added to the prerequisites.
@end itemize
@end ifinfo

@node Rule Syntax, Wildcards, Rule Example, Rules
@section Rule Syntax

@cindex rule syntax
@cindex syntax of rules
In general, a rule looks like this:

@example
@var{targets} : @var{prerequisites}
        @var{command}
        @dots{}
@end example

@noindent
or like this:

@example
@var{targets} : @var{prerequisites} ; @var{command}
        @var{command}
        @dots{}
@end example

@cindex targets
@cindex rule targets
The @var{targets} are file names, separated by spaces.  Wildcard
characters may be used (@pxref{Wildcards, ,Using Wildcard Characters
in File Names}) and a name of the form @file{@var{a}(@var{m})}
represents member @var{m} in archive file @var{a}
(@pxref{Archive Members, ,Archive Members as Targets}).
Usually there is only one
target per rule, but occasionally there is a reason to have more
(@pxref{Multiple Targets, , Multiple Targets in a Rule}).@refill

@cindex commands
@cindex tab character (in commands)
The @var{command} lines start with a tab character.  The first command may
appear on the line after the prerequisites, with a tab character, or may
appear on the same line, with a semicolon.  Either way, the effect is the
same.  @xref{Commands, ,Writing the Commands in Rules}.

@cindex dollar sign (@code{$}), in rules
@cindex @code{$}, in rules
@cindex rule, and @code{$}
Because dollar signs are used to start variable references, if you really
want a dollar sign in a rule you must write two of them, @samp{$$}
(@pxref{Using Variables, ,How to Use Variables}).
You may split a long line by inserting a backslash
followed by a newline, but this is not required, as @code{make} places no
limit on the length of a line in a makefile.

A rule tells @code{make} two things: when the targets are out of date,
and how to update them when necessary.

@cindex prerequisites
@cindex rule prerequisites
The criterion for being out of date is specified in terms of the
@var{prerequisites}, which consist of file names separated by spaces.
(Wildcards and archive members (@pxref{Archives}) are allowed here too.)
A target is out of date if it does not exist or if it is older than any
of the prerequisites (by comparison of last-modification times).  The
idea is that the contents of the target file are computed based on
information in the prerequisites, so if any of the prerequisites changes,
the contents of the existing target file are no longer necessarily
valid.

How to update is specified by @var{commands}.  These are lines to be
executed by the shell (normally @samp{sh}), but with some extra features
(@pxref{Commands, ,Writing the Commands in Rules}).

@node Wildcards, Directory Search, Rule Syntax, Rules
@section Using Wildcard Characters in File Names
@cindex wildcard
@cindex file name with wildcards
@cindex globbing (wildcards)

@cindex @code{*} (wildcard character)
@cindex @code{?} (wildcard character)
@cindex @code{[@dots{}]} (wildcard characters)
A single file name can specify many files using @dfn{wildcard characters}.
The wildcard characters in @code{make} are @samp{*}, @samp{?} and
@samp{[@dots{}]}, the same as in the Bourne shell.  For example, @file{*.c}
specifies a list of all the files (in the working directory) whose names
end in @samp{.c}.@refill

@cindex @code{~} (tilde)
@cindex tilde (@code{~})
@cindex home directory
The character @samp{~} at the beginning of a file name also has special
significance.  If alone, or followed by a slash, it represents your home
directory.  For example @file{~/bin} expands to @file{/home/you/bin}.
If the @samp{~} is followed by a word, the string represents the home
directory of the user named by that word.  For example @file{~john/bin}
expands to @file{/home/john/bin}.  On systems which don't have a home
directory for each user (such as MS-DOS or MS-Windows), this
functionality can be simulated by setting the environment variable
@var{HOME}.@refill

Wildcard expansion happens automatically in targets, in prerequisites,
and in commands (where the shell does the expansion).  In other
contexts, wildcard expansion happens only if you request it explicitly
with the @code{wildcard} function.

The special significance of a wildcard character can be turned off by
preceding it with a backslash.  Thus, @file{foo\*bar} would refer to a
specific file whose name consists of @samp{foo}, an asterisk, and
@samp{bar}.@refill

@menu
* Wildcard Examples::           Several examples
* Wildcard Pitfall::            Problems to avoid.
* Wildcard Function::           How to cause wildcard expansion where
                                  it does not normally take place.
@end menu

@node Wildcard Examples, Wildcard Pitfall,  , Wildcards
@subsection Wildcard Examples

Wildcards can be used in the commands of a rule, where they are expanded
by the shell.  For example, here is a rule to delete all the object files:

@example
@group
clean:
        rm -f *.o
@end group
@end example
@cindex @code{rm} (shell command)

Wildcards are also useful in the prerequisites of a rule.  With the
following rule in the makefile, @samp{make print} will print all the
@samp{.c} files that have changed since the last time you printed them:

@example
print: *.c
        lpr -p $?
        touch print
@end example

@cindex @code{print} target
@cindex @code{lpr} (shell command)
@cindex @code{touch} (shell command)
@noindent
This rule uses @file{print} as an empty target file; see @ref{Empty
Targets, ,Empty Target Files to Record Events}.  (The automatic variable
@samp{$?} is used to print only those files that have changed; see
@ref{Automatic, ,Automatic Variables}.)@refill

Wildcard expansion does not happen when you define a variable.  Thus, if
you write this:

@example
objects = *.o
@end example

@noindent
then the value of the variable @code{objects} is the actual string
@samp{*.o}.  However, if you use the value of @code{objects} in a target,
prerequisite or command, wildcard expansion will take place at that time.
To set @code{objects} to the expansion, instead use:

@example
objects := $(wildcard *.o)
@end example

@noindent
@xref{Wildcard Function}.

@node Wildcard Pitfall, Wildcard Function, Wildcard Examples, Wildcards
@subsection Pitfalls of Using Wildcards
@cindex wildcard pitfalls
@cindex pitfalls of wildcards
@cindex mistakes with wildcards
@cindex errors with wildcards
@cindex problems with wildcards

Now here is an example of a naive way of using wildcard expansion, that
does not do what you would intend.  Suppose you would like to say that the
executable file @file{foo} is made from all the object files in the
directory, and you write this:

@example
objects = *.o

foo : $(objects)
        cc -o foo $(CFLAGS) $(objects)
@end example

@noindent
The value of @code{objects} is the actual string @samp{*.o}.  Wildcard
expansion happens in the rule for @file{foo}, so that each @emph{existing}
@samp{.o} file becomes a prerequisite of @file{foo} and will be recompiled if
necessary.

But what if you delete all the @samp{.o} files?  When a wildcard matches
no files, it is left as it is, so then @file{foo} will depend on the
oddly-named file @file{*.o}.  Since no such file is likely to exist,
@code{make} will give you an error saying it cannot figure out how to
make @file{*.o}.  This is not what you want!

Actually it is possible to obtain the desired result with wildcard
expansion, but you need more sophisticated techniques, including the
@code{wildcard} function and string substitution.
@ifinfo
@xref{Wildcard Function, ,The Function @code{wildcard}}.
@end ifinfo
@iftex
These are described in the following section.
@end iftex

@cindex wildcards and MS-DOS/MS-Windows backslashes
@cindex backslashes in pathnames and wildcard expansion

Microsoft operating systems (MS-DOS and MS-Windows) use backslashes to
separate directories in pathnames, like so:

@example
  c:\foo\bar\baz.c
@end example

This is equivalent to the Unix-style @file{c:/foo/bar/baz.c} (the
@file{c:} part is the so-called drive letter).  When @code{make} runs on
these systems, it supports backslashes as well as the Unix-style forward
slashes in pathnames.  However, this support does @emph{not} include the
wildcard expansion, where backslash is a quote character.  Therefore,
you @emph{must} use Unix-style slashes in these cases.


@node Wildcard Function,  , Wildcard Pitfall, Wildcards
@subsection The Function @code{wildcard}
@findex wildcard

Wildcard expansion happens automatically in rules.  But wildcard expansion
does not normally take place when a variable is set, or inside the
arguments of a function.  If you want to do wildcard expansion in such
places, you need to use the @code{wildcard} function, like this:

@example
$(wildcard @var{pattern}@dots{})
@end example

@noindent
This string, used anywhere in a makefile, is replaced by a
space-separated list of names of existing files that match one of the
given file name patterns.  If no existing file name matches a pattern,
then that pattern is omitted from the output of the @code{wildcard}
function.  Note that this is different from how unmatched wildcards
behave in rules, where they are used verbatim rather than ignored
(@pxref{Wildcard Pitfall}).

One use of the @code{wildcard} function is to get a list of all the C source
files in a directory, like this:

@example
$(wildcard *.c)
@end example

We can change the list of C source files into a list of object files by
replacing the @samp{.c} suffix with @samp{.o} in the result, like this:

@example
$(patsubst %.c,%.o,$(wildcard *.c))
@end example

@noindent
(Here we have used another function, @code{patsubst}.
@xref{Text Functions, ,Functions for String Substitution and Analysis}.)@refill

Thus, a makefile to compile all C source files in the directory and then
link them together could be written as follows:

@example
objects := $(patsubst %.c,%.o,$(wildcard *.c))

foo : $(objects)
        cc -o foo $(objects)
@end example

@noindent
(This takes advantage of the implicit rule for compiling C programs, so
there is no need to write explicit rules for compiling the files.
@xref{Flavors, ,The Two Flavors of Variables}, for an explanation of
@samp{:=}, which is a variant of @samp{=}.)

@node Directory Search, Phony Targets, Wildcards, Rules
@section Searching Directories for Prerequisites
@vindex VPATH
@findex vpath
@cindex vpath
@cindex search path for prerequisites (@code{VPATH})
@cindex directory search (@code{VPATH})

For large systems, it is often desirable to put sources in a separate
directory from the binaries.  The @dfn{directory search} features of
@code{make} facilitate this by searching several directories
automatically to find a prerequisite.  When you redistribute the files
among directories, you do not need to change the individual rules,
just the search paths.

@menu
* General Search::              Specifying a search path that applies
                                  to every prerequisite.
* Selective Search::            Specifying a search path
                                  for a specified class of names.
* Search Algorithm::            When and how search paths are applied.
* Commands/Search::             How to write shell commands that work together
                                  with search paths.
* Implicit/Search::             How search paths affect implicit rules.
* Libraries/Search::            Directory search for link libraries.
@end menu

@node General Search, Selective Search,  , Directory Search
@subsection @code{VPATH}: Search Path for All Prerequisites
@vindex VPATH

The value of the @code{make} variable @code{VPATH} specifies a list of
directories that @code{make} should search.  Most often, the
directories are expected to contain prerequisite files that are not in the
current directory; however, @code{VPATH} specifies a search list that
@code{make} applies for all files, including files which are targets of
rules.

Thus, if a file that is listed as a target or prerequisite does not exist
in the current directory, @code{make} searches the directories listed in
@code{VPATH} for a file with that name.  If a file is found in one of
them, that file may become the prerequisite (see below).  Rules may then
specify the names of files in the prerequisite list as if they all
existed in the current directory.  @xref{Commands/Search, ,Writing Shell
Commands with Directory Search}.

In the @code{VPATH} variable, directory names are separated by colons or
blanks.  The order in which directories are listed is the order followed
by @code{make} in its search.  (On MS-DOS and MS-Windows, semi-colons
are used as separators of directory names in @code{VPATH}, since the
colon can be used in the pathname itself, after the drive letter.)

For example,

@example
VPATH = src:../headers
@end example

@noindent
specifies a path containing two directories, @file{src} and
@file{../headers}, which @code{make} searches in that order.

With this value of @code{VPATH}, the following rule,

@example
foo.o : foo.c
@end example

@noindent
is interpreted as if it were written like this:

@example
foo.o : src/foo.c
@end example

@noindent
assuming the file @file{foo.c} does not exist in the current directory but
is found in the directory @file{src}.

@node Selective Search, Search Algorithm, General Search, Directory Search
@subsection The @code{vpath} Directive
@findex vpath

Similar to the @code{VPATH} variable, but more selective, is the
@code{vpath} directive (note lower case), which allows you to specify a
search path for a particular class of file names: those that match a
particular pattern.  Thus you can supply certain search directories for
one class of file names and other directories (or none) for other file
names.

There are three forms of the @code{vpath} directive:

@table @code
@item vpath @var{pattern} @var{directories}
Specify the search path @var{directories} for file names that match
@var{pattern}.

The search path, @var{directories}, is a list of directories to be
searched, separated by colons (semi-colons on MS-DOS and MS-Windows) or
blanks, just like the search path used in the @code{VPATH} variable.

@item vpath @var{pattern}
Clear out the search path associated with @var{pattern}.

@c Extra blank line makes sure this gets two lines.
@item vpath

Clear all search paths previously specified with @code{vpath} directives.
@end table

A @code{vpath} pattern is a string containing a @samp{%} character.  The
string must match the file name of a prerequisite that is being searched
for, the @samp{%} character matching any sequence of zero or more
characters (as in pattern rules; @pxref{Pattern Rules, ,Defining and
Redefining Pattern Rules}).  For example, @code{%.h} matches files that
end in @code{.h}.  (If there is no @samp{%}, the pattern must match the
prerequisite exactly, which is not useful very often.)

@cindex @code{%}, quoting in @code{vpath}
@cindex @code{%}, quoting with @code{\} (backslash)
@cindex @code{\} (backslash), to quote @code{%}
@cindex backslash (@code{\}), to quote @code{%}
@cindex quoting @code{%}, in @code{vpath}
@samp{%} characters in a @code{vpath} directive's pattern can be quoted
with preceding backslashes (@samp{\}).  Backslashes that would otherwise
quote @samp{%} characters can be quoted with more backslashes.
Backslashes that quote @samp{%} characters or other backslashes are
removed from the pattern before it is compared to file names.  Backslashes
that are not in danger of quoting @samp{%} characters go unmolested.@refill

When a prerequisite fails to exist in the current directory, if the
@var{pattern} in a @code{vpath} directive matches the name of the
prerequisite file, then the @var{directories} in that directive are searched
just like (and before) the directories in the @code{VPATH} variable.

For example,

@example
vpath %.h ../headers
@end example

@noindent
tells @code{make} to look for any prerequisite whose name ends in @file{.h}
in the directory @file{../headers} if the file is not found in the current
directory.

If several @code{vpath} patterns match the prerequisite file's name, then
@code{make} processes each matching @code{vpath} directive one by one,
searching all the directories mentioned in each directive.  @code{make}
handles multiple @code{vpath} directives in the order in which they
appear in the makefile; multiple directives with the same pattern are
independent of each other.

@need 750
Thus,

@example
@group
vpath %.c foo
vpath %   blish
vpath %.c bar
@end group
@end example

@noindent
will look for a file ending in @samp{.c} in @file{foo}, then
@file{blish}, then @file{bar}, while

@example
@group
vpath %.c foo:bar
vpath %   blish
@end group
@end example

@noindent
will look for a file ending in @samp{.c} in @file{foo}, then
@file{bar}, then @file{blish}.

@node Search Algorithm, Commands/Search, Selective Search, Directory Search
@subsection How Directory Searches are Performed
@cindex algorithm for directory search
@cindex directory search algorithm

When a prerequisite is found through directory search, regardless of type
(general or selective), the pathname located may not be the one that
@code{make} actually provides you in the prerequisite list.  Sometimes
the path discovered through directory search is thrown away.

The algorithm @code{make} uses to decide whether to keep or abandon a
path found via directory search is as follows:

@enumerate
@item
If a target file does not exist at the path specified in the makefile,
directory search is performed.

@item
If the directory search is successful, that path is kept and this file
is tentatively stored as the target.

@item
All prerequisites of this target are examined using this same method.

@item
After processing the prerequisites, the target may or may not need to be
rebuilt:

@enumerate a
@item
If the target does @emph{not} need to be rebuilt, the path to the file
found during directory search is used for any prerequisite lists which
contain this target.  In short, if @code{make} doesn't need to rebuild
the target then you use the path found via directory search.

@item
If the target @emph{does} need to be rebuilt (is out-of-date), the
pathname found during directory search is @emph{thrown away}, and the
target is rebuilt using the file name specified in the makefile.  In
short, if @code{make} must rebuild, then the target is rebuilt locally,
not in the directory found via directory search.
@end enumerate
@end enumerate

This algorithm may seem complex, but in practice it is quite often
exactly what you want.

@cindex traditional directory search
@cindex directory search, traditional
Other versions of @code{make} use a simpler algorithm: if the file does
not exist, and it is found via directory search, then that pathname is
always used whether or not the target needs to be built.  Thus, if the
target is rebuilt it is created at the pathname discovered during
directory search.

@vindex GPATH
If, in fact, this is the behavior you want for some or all of your
directories, you can use the @code{GPATH} variable to indicate this to
@code{make}.

@code{GPATH} has the same syntax and format as @code{VPATH} (that is, a
space- or colon-delimited list of pathnames).  If an out-of-date target
is found by directory search in a directory that also appears in
@code{GPATH}, then that pathname is not thrown away.  The target is
rebuilt using the expanded path.

@node Commands/Search, Implicit/Search, Search Algorithm, Directory Search
@subsection Writing Shell Commands with Directory Search
@cindex shell command, and directory search
@cindex directory search (@code{VPATH}), and shell commands

When a prerequisite is found in another directory through directory search,
this cannot change the commands of the rule; they will execute as written.
Therefore, you must write the commands with care so that they will look for
the prerequisite in the directory where @code{make} finds it.

This is done with the @dfn{automatic variables} such as @samp{$^}
(@pxref{Automatic, ,Automatic Variables}).
For instance, the value of @samp{$^} is a
list of all the prerequisites of the rule, including the names of
the directories in which they were found, and the value of
@samp{$@@} is the target.  Thus:@refill

@example
foo.o : foo.c
        cc -c $(CFLAGS) $^ -o $@@
@end example

@noindent
(The variable @code{CFLAGS} exists so you can specify flags for C
compilation by implicit rules; we use it here for consistency so it will
affect all C compilations uniformly;
@pxref{Implicit Variables, ,Variables Used by Implicit Rules}.)

Often the prerequisites include header files as well, which you do not
want to mention in the commands.  The automatic variable @samp{$<} is
just the first prerequisite:

@example
VPATH = src:../headers
foo.o : foo.c defs.h hack.h
        cc -c $(CFLAGS) $< -o $@@
@end example

@node Implicit/Search, Libraries/Search, Commands/Search, Directory Search
@subsection Directory Search and Implicit Rules
@cindex @code{VPATH}, and implicit rules
@cindex directory search (@code{VPATH}), and implicit rules
@cindex search path for prerequisites (@code{VPATH}), and implicit rules
@cindex implicit rule, and directory search
@cindex implicit rule, and @code{VPATH}
@cindex rule, implicit, and directory search
@cindex rule, implicit, and @code{VPATH}

The search through the directories specified in @code{VPATH} or with
@code{vpath} also happens during consideration of implicit rules
(@pxref{Implicit Rules, ,Using Implicit Rules}).

For example, when a file @file{foo.o} has no explicit rule, @code{make}
considers implicit rules, such as the built-in rule to compile
@file{foo.c} if that file exists.  If such a file is lacking in the
current directory, the appropriate directories are searched for it.  If
@file{foo.c} exists (or is mentioned in the makefile) in any of the
directories, the implicit rule for C compilation is applied.

The commands of implicit rules normally use automatic variables as a
matter of necessity; consequently they will use the file names found by
directory search with no extra effort.

@node Libraries/Search,  , Implicit/Search, Directory Search
@subsection Directory Search for Link Libraries
@cindex link libraries, and directory search
@cindex libraries for linking, directory search
@cindex directory search (@code{VPATH}), and link libraries
@cindex @code{VPATH}, and link libraries
@cindex search path for prerequisites (@code{VPATH}), and link libraries
@cindex @code{-l} (library search)
@cindex link libraries, patterns matching
@cindex @code{.LIBPATTERNS}, and link libraries
@vindex .LIBPATTERNS

Directory search applies in a special way to libraries used with the
linker.  This special feature comes into play when you write a prerequisite
whose name is of the form @samp{-l@var{name}}.  (You can tell something
strange is going on here because the prerequisite is normally the name of a
file, and the @emph{file name} of a library generally looks like
@file{lib@var{name}.a}, not like @samp{-l@var{name}}.)@refill

When a prerequisite's name has the form @samp{-l@var{name}}, @code{make}
handles it specially by searching for the file @file{lib@var{name}.so} in
the current directory, in directories specified by matching @code{vpath}
search paths and the @code{VPATH} search path, and then in the
directories @file{/lib}, @file{/usr/lib}, and @file{@var{prefix}/lib}
(normally @file{/usr/local/lib}, but MS-DOS/MS-Windows versions of
@code{make} behave as if @var{prefix} is defined to be the root of the
DJGPP installation tree).

If that file is not found, then the file @file{lib@var{name}.a} is
searched for, in the same directories as above.

For example, if there is a @file{/usr/lib/libcurses.a} library on your
system (and no @file{/usr/lib/libcurses.so} file), then

@example
@group
foo : foo.c -lcurses
        cc $^ -o $@@
@end group
@end example

@noindent
would cause the command @samp{cc foo.c /usr/lib/libcurses.a -o foo} to
be executed when @file{foo} is older than @file{foo.c} or than
@file{/usr/lib/libcurses.a}.@refill

Although the default set of files to be searched for is
@file{lib@var{name}.so} and @file{lib@var{name}.a}, this is customizable
via the @code{.LIBPATTERNS} variable.  Each word in the value of this
variable is a pattern string.  When a prerequisite like
@samp{-l@var{name}} is seen, @code{make} will replace the percent in
each pattern in the list with @var{name} and perform the above directory
searches using that library filename.  If no library is found, the next
word in the list will be used.

The default value for @code{.LIBPATTERNS} is ``@samp{lib%.so lib%.a}'',
which provides the default behavior described above.

You can turn off link library expansion completely by setting this
variable to an empty value.

@node Phony Targets, Force Targets, Directory Search, Rules
@section Phony Targets
@cindex phony targets
@cindex targets, phony
@cindex targets without a file

A phony target is one that is not really the name of a file.  It is just a
name for some commands to be executed when you make an explicit request.
There are two reasons to use a phony target: to avoid a conflict with
a file of the same name, and to improve performance.

If you write a rule whose commands will not create the target file, the
commands will be executed every time the target comes up for remaking.
Here is an example:

@example
@group
clean:
        rm *.o temp
@end group
@end example

@noindent
Because the @code{rm} command does not create a file named @file{clean},
probably no such file will ever exist.  Therefore, the @code{rm} command
will be executed every time you say @samp{make clean}.
@cindex @code{rm} (shell command)

@findex .PHONY
The phony target will cease to work if anything ever does create a file
named @file{clean} in this directory.  Since it has no prerequisites, the
file @file{clean} would inevitably be considered up to date, and its
commands would not be executed.  To avoid this problem, you can explicitly
declare the target to be phony, using the special target @code{.PHONY}
(@pxref{Special Targets, ,Special Built-in Target Names}) as follows:

@example
.PHONY : clean
@end example

@noindent
Once this is done, @samp{make clean} will run the commands regardless of
whether there is a file named @file{clean}.

Since it knows that phony targets do not name actual files that could be
remade from other files, @code{make} skips the implicit rule search for
phony targets (@pxref{Implicit Rules}).  This is why declaring a target
phony is good for performance, even if you are not worried about the
actual file existing.

Thus, you first write the line that states that @code{clean} is a
phony target, then you write the rule, like this:

@example
@group
.PHONY: clean
clean:
        rm *.o temp
@end group
@end example

Another example of the usefulness of phony targets is in conjunction
with recursive invocations of @code{make}.  In this case the makefile
will often contain a variable which lists a number of subdirectories to
be built.  One way to handle this is with one rule whose command is a
shell loop over the subdirectories, like this:

@example
@group
SUBDIRS = foo bar baz

subdirs:
        for dir in $(SUBDIRS); do \
          $(MAKE) -C $$dir; \
        done
@end group
@end example

There are a few of problems with this method, however.  First, any error
detected in a submake is not noted by this rule, so it will continue to
build the rest of the directories even when one fails.  This can be
overcome by adding shell commands to note the error and exit, but then
it will do so even if @code{make} is invoked with the @code{-k} option,
which is unfortunate.  Second, and perhaps more importantly, you cannot
take advantage of the parallel build capabilities of make using this
method, since there is only one rule.

By declaring the subdirectories as phony targets (you must do this as
the subdirectory obviously always exists; otherwise it won't be built)
you can remove these problems:

@example
@group
SUBDIRS = foo bar baz

.PHONY: subdirs $(SUBDIRS)

subdirs: $(SUBDIRS)

$(SUBDIRS):
        $(MAKE) -C $@

foo: baz
@end group
@end example

Here we've also declared that the @file{foo} subdirectory cannot be
built until after the @file{baz} subdirectory is complete; this kind of
relationship declaration is particularly important when attempting
parallel builds.

A phony target should not be a prerequisite of a real target file; if it
is, its commands are run every time @code{make} goes to update that
file.  As long as a phony target is never a prerequisite of a real
target, the phony target commands will be executed only when the phony
target is a specified goal (@pxref{Goals, ,Arguments to Specify the
Goals}).

Phony targets can have prerequisites.  When one directory contains multiple
programs, it is most convenient to describe all of the programs in one
makefile @file{./Makefile}.  Since the target remade by default will be the
first one in the makefile, it is common to make this a phony target named
@samp{all} and give it, as prerequisites, all the individual programs.  For
example:

@example
all : prog1 prog2 prog3
.PHONY : all

prog1 : prog1.o utils.o
        cc -o prog1 prog1.o utils.o

prog2 : prog2.o
        cc -o prog2 prog2.o

prog3 : prog3.o sort.o utils.o
        cc -o prog3 prog3.o sort.o utils.o
@end example

@noindent
Now you can say just @samp{make} to remake all three programs, or specify
as arguments the ones to remake (as in @samp{make prog1 prog3}).

When one phony target is a prerequisite of another, it serves as a subroutine
of the other.  For example, here @samp{make cleanall} will delete the
object files, the difference files, and the file @file{program}:

@example
.PHONY: cleanall cleanobj cleandiff

cleanall : cleanobj cleandiff
        rm program

cleanobj :
        rm *.o

cleandiff :
        rm *.diff
@end example

@node Force Targets, Empty Targets, Phony Targets, Rules
@section Rules without Commands or Prerequisites
@cindex force targets
@cindex targets, force
@cindex @code{FORCE}
@cindex rule, no commands or prerequisites

If a rule has no prerequisites or commands, and the target of the rule
is a nonexistent file, then @code{make} imagines this target to have
been updated whenever its rule is run.  This implies that all targets
depending on this one will always have their commands run.

An example will illustrate this:

@example
@group
clean: FORCE
        rm $(objects)
FORCE:
@end group
@end example

Here the target @samp{FORCE} satisfies the special conditions, so the
target @file{clean} that depends on it is forced to run its commands.
There is nothing special about the name @samp{FORCE}, but that is one name
commonly used this way.

As you can see, using @samp{FORCE} this way has the same results as using
@samp{.PHONY: clean}.

Using @samp{.PHONY} is more explicit and more efficient.  However,
other versions of @code{make} do not support @samp{.PHONY}; thus
@samp{FORCE} appears in many makefiles.  @xref{Phony Targets}.

@node Empty Targets, Special Targets, Force Targets, Rules
@section Empty Target Files to Record Events
@cindex empty targets
@cindex targets, empty
@cindex recording events with empty targets

The @dfn{empty target} is a variant of the phony target; it is used to hold
commands for an action that you request explicitly from time to time.
Unlike a phony target, this target file can really exist; but the file's
contents do not matter, and usually are empty.

The purpose of the empty target file is to record, with its
last-modification time, when the rule's commands were last executed.  It
does so because one of the commands is a @code{touch} command to update the
target file.

The empty target file should have some prerequisites (otherwise it
doesn't make sense).  When you ask to remake the empty target, the
commands are executed if any prerequisite is more recent than the target;
in other words, if a prerequisite has changed since the last time you
remade the target.  Here is an example:

@example
print: foo.c bar.c
        lpr -p $?
        touch print
@end example
@cindex @code{print} target
@cindex @code{lpr} (shell command)
@cindex @code{touch} (shell command)

@noindent
With this rule, @samp{make print} will execute the @code{lpr} command if
either source file has changed since the last @samp{make print}.  The
automatic variable @samp{$?} is used to print only those files that have
changed (@pxref{Automatic, ,Automatic Variables}).

@node Special Targets, Multiple Targets, Empty Targets, Rules
@section Special Built-in Target Names
@cindex special targets
@cindex built-in special targets
@cindex targets, built-in special

Certain names have special meanings if they appear as targets.

@table @code
@findex .PHONY
@item .PHONY

The prerequisites of the special target @code{.PHONY} are considered to
be phony targets.  When it is time to consider such a target,
@code{make} will run its commands unconditionally, regardless of
whether a file with that name exists or what its last-modification
time is.  @xref{Phony Targets, ,Phony Targets}.

@findex .SUFFIXES
@item .SUFFIXES

The prerequisites of the special target @code{.SUFFIXES} are the list
of suffixes to be used in checking for suffix rules.
@xref{Suffix Rules, , Old-Fashioned Suffix Rules}.

@findex .DEFAULT
@item .DEFAULT

The commands specified for @code{.DEFAULT} are used for any target for
which no rules are found (either explicit rules or implicit rules).
@xref{Last Resort}.  If @code{.DEFAULT} commands are specified, every
file mentioned as a prerequisite, but not as a target in a rule, will have
these commands executed on its behalf.  @xref{Implicit Rule Search,
,Implicit Rule Search Algorithm}.

@findex .PRECIOUS
@item .PRECIOUS
@cindex precious targets
@cindex preserving with @code{.PRECIOUS}

The targets which @code{.PRECIOUS} depends on are given the following
special treatment: if @code{make} is killed or interrupted during the
execution of their commands, the target is not deleted.
@xref{Interrupts, ,Interrupting or Killing @code{make}}.
Also, if the target is an intermediate file, it will not be deleted
after it is no longer needed, as is normally done.
@xref{Chained Rules, ,Chains of Implicit Rules}.

You can also list the target pattern of an implicit rule (such as
@samp{%.o}) as a prerequisite file of the special target @code{.PRECIOUS}
to preserve intermediate files created by rules whose target patterns
match that file's name.

@findex .INTERMEDIATE
@item .INTERMEDIATE
@cindex intermediate targets, explicit

The targets which @code{.INTERMEDIATE} depends on are treated as
intermediate files.  @xref{Chained Rules, ,Chains of Implicit Rules}.
@code{.INTERMEDIATE} with no prerequisites has no effect.

@findex .SECONDARY
@item .SECONDARY
@cindex secondary targets
@cindex preserving with @code{.SECONDARY}

The targets which @code{.SECONDARY} depends on are treated as
intermediate files, except that they are never automatically deleted.
@xref{Chained Rules, ,Chains of Implicit Rules}.

@code{.SECONDARY} with no prerequisites marks all file targets mentioned
in the makefile as secondary.

@findex .DELETE_ON_ERROR
@item .DELETE_ON_ERROR
@cindex removing targets on failure

If @code{.DELETE_ON_ERROR} is mentioned as a target anywhere in the
makefile, then @code{make} will delete the target of a rule if it has
changed and its commands exit with a nonzero exit status, just as it
does when it receives a signal.  @xref{Errors, ,Errors in Commands}.

@findex .IGNORE
@item .IGNORE

If you specify prerequisites for @code{.IGNORE}, then @code{make} will
ignore errors in execution of the commands run for those particular
files.  The commands for @code{.IGNORE} are not meaningful.

If mentioned as a target with no prerequisites, @code{.IGNORE} says to
ignore errors in execution of commands for all files.  This usage of
@samp{.IGNORE} is supported only for historical compatibility.  Since
this affects every command in the makefile, it is not very useful; we
recommend you use the more selective ways to ignore errors in specific
commands.  @xref{Errors, ,Errors in Commands}.

@findex .SILENT
@item .SILENT

If you specify prerequisites for @code{.SILENT}, then @code{make} will
not print the commands to remake those particular files before executing
them.  The commands for @code{.SILENT} are not meaningful.

If mentioned as a target with no prerequisites, @code{.SILENT} says not
to print any commands before executing them.  This usage of
@samp{.SILENT} is supported only for historical compatibility.  We
recommend you use the more selective ways to silence specific commands.
@xref{Echoing, ,Command Echoing}.  If you want to silence all commands
for a particular run of @code{make}, use the @samp{-s} or
@w{@samp{--silent}} option (@pxref{Options Summary}).

@findex .EXPORT_ALL_VARIABLES
@item .EXPORT_ALL_VARIABLES

Simply by being mentioned as a target, this tells @code{make} to
export all variables to child processes by default.
@xref{Variables/Recursion, ,Communicating Variables to a
Sub-@code{make}}.

@findex .NOTPARALLEL
@item .NOTPARALLEL
@cindex parallel execution, overriding

If @code{.NOTPARALLEL} is mentioned as a target, then this invocation of
@code{make} will be run serially, even if the @samp{-j} option is
given.  Any recursively invoked @code{make} command will still be run in
parallel (unless its makefile contains this target).  Any prerequisites
on this target are ignored.
@end table

Any defined implicit rule suffix also counts as a special target if it
appears as a target, and so does the concatenation of two suffixes, such
as @samp{.c.o}.  These targets are suffix rules, an obsolete way of
defining implicit rules (but a way still widely used).  In principle, any
target name could be special in this way if you break it in two and add
both pieces to the suffix list.  In practice, suffixes normally begin with
@samp{.}, so these special target names also begin with @samp{.}.
@xref{Suffix Rules, ,Old-Fashioned Suffix Rules}.

@node Multiple Targets, Multiple Rules, Special Targets, Rules
@section Multiple Targets in a Rule
@cindex multiple targets
@cindex several targets in a rule
@cindex targets, multiple
@cindex rule, with multiple targets

A rule with multiple targets is equivalent to writing many rules, each with
one target, and all identical aside from that.  The same commands apply to
all the targets, but their effects may vary because you can substitute the
actual target name into the command using @samp{$@@}.  The rule contributes
the same prerequisites to all the targets also.

This is useful in two cases.

@itemize @bullet
@item
You want just prerequisites, no commands.  For example:

@example
kbd.o command.o files.o: command.h
@end example

@noindent
gives an additional prerequisite to each of the three object files
mentioned.

@item
Similar commands work for all the targets.  The commands do not need
to be absolutely identical, since the automatic variable @samp{$@@}
can be used to substitute the particular target to be remade into the
commands (@pxref{Automatic, ,Automatic Variables}).  For example:

@example
@group
bigoutput littleoutput : text.g
        generate text.g -$(subst output,,$@@) > $@@
@end group
@end example
@findex subst

@noindent
is equivalent to

@example
bigoutput : text.g
        generate text.g -big > bigoutput
littleoutput : text.g
        generate text.g -little > littleoutput
@end example

@noindent
Here we assume the hypothetical program @code{generate} makes two
types of output, one if given @samp{-big} and one if given
@samp{-little}.
@xref{Text Functions, ,Functions for String Substitution and Analysis},
for an explanation of the @code{subst} function.
@end itemize

Suppose you would like to vary the prerequisites according to the target,
much as the variable @samp{$@@} allows you to vary the commands.
You cannot do this with multiple targets in an ordinary rule, but you can
do it with a @dfn{static pattern rule}.
@xref{Static Pattern, ,Static Pattern Rules}.

@node Multiple Rules, Static Pattern, Multiple Targets, Rules
@section Multiple Rules for One Target
@cindex multiple rules for one target
@cindex several rules for one target
@cindex rule, multiple for one target
@cindex target, multiple rules for one

One file can be the target of several rules.  All the prerequisites
mentioned in all the rules are merged into one list of prerequisites for
the target.  If the target is older than any prerequisite from any rule,
the commands are executed.

There can only be one set of commands to be executed for a file.
If more than one rule gives commands for the same file,
@code{make} uses the last set given and prints an error message.
(As a special case, if the file's name begins with a dot, no
error message is printed.  This odd behavior is only for
compatibility with other implementations of @code{make}.)
There is no reason to
write your makefiles this way; that is why @code{make} gives you
an error message.@refill

An extra rule with just prerequisites can be used to give a few extra
prerequisites to many files at once.  For example, one usually has a
variable named @code{objects} containing a list of all the compiler output
files in the system being made.  An easy way to say that all of them must
be recompiled if @file{config.h} changes is to write the following:

@example
objects = foo.o bar.o
foo.o : defs.h
bar.o : defs.h test.h
$(objects) : config.h
@end example

This could be inserted or taken out without changing the rules that really
specify how to make the object files, making it a convenient form to use if
you wish to add the additional prerequisite intermittently.

Another wrinkle is that the additional prerequisites could be specified with
a variable that you set with a command argument to @code{make}
(@pxref{Overriding, ,Overriding Variables}).  For example,

@example
@group
extradeps=
$(objects) : $(extradeps)
@end group
@end example

@noindent
means that the command @samp{make extradeps=foo.h} will consider
@file{foo.h} as a prerequisite of each object file, but plain @samp{make}
will not.

If none of the explicit rules for a target has commands, then @code{make}
searches for an applicable implicit rule to find some commands
@pxref{Implicit Rules, ,Using Implicit Rules}).

@node Static Pattern, Double-Colon, Multiple Rules, Rules
@section Static Pattern Rules
@cindex static pattern rule
@cindex rule, static pattern
@cindex pattern rules, static (not implicit)
@cindex varying prerequisites
@cindex prerequisites, varying (static pattern)

@dfn{Static pattern rules} are rules which specify multiple targets and
construct the prerequisite names for each target based on the target name.
They are more general than ordinary rules with multiple targets because the
targets do not have to have identical prerequisites.  Their prerequisites must
be @emph{analogous}, but not necessarily @emph{identical}.

@menu
* Static Usage::                The syntax of static pattern rules.
* Static versus Implicit::      When are they better than implicit rules?
@end menu

@node Static Usage, Static versus Implicit,  , Static Pattern
@subsection Syntax of Static Pattern Rules
@cindex static pattern rule, syntax of
@cindex pattern rules, static, syntax of

Here is the syntax of a static pattern rule:

@example
@var{targets} @dots{}: @var{target-pattern}: @var{dep-patterns} @dots{}
        @var{commands}
        @dots{}
@end example

@noindent
The @var{targets} list specifies the targets that the rule applies to.
The targets can contain wildcard characters, just like the targets of
ordinary rules (@pxref{Wildcards, ,Using Wildcard Characters in File
Names}).

@cindex target pattern, static (not implicit)
@cindex stem
The @var{target-pattern} and @var{dep-patterns} say how to compute the
prerequisites of each target.  Each target is matched against the
@var{target-pattern} to extract a part of the target name, called the
@dfn{stem}.  This stem is substituted into each of the @var{dep-patterns}
to make the prerequisite names (one from each @var{dep-pattern}).

Each pattern normally contains the character @samp{%} just once.  When the
@var{target-pattern} matches a target, the @samp{%} can match any part of
the target name; this part is called the @dfn{stem}.  The rest of the
pattern must match exactly.  For example, the target @file{foo.o} matches
the pattern @samp{%.o}, with @samp{foo} as the stem.  The targets
@file{foo.c} and @file{foo.out} do not match that pattern.@refill

@cindex prerequisite pattern, static (not implicit)
The prerequisite names for each target are made by substituting the stem
for the @samp{%} in each prerequisite pattern.  For example, if one
prerequisite pattern is @file{%.c}, then substitution of the stem
@samp{foo} gives the prerequisite name @file{foo.c}.  It is legitimate
to write a prerequisite pattern that does not contain @samp{%}; then this
prerequisite is the same for all targets.

@cindex @code{%}, quoting in static pattern
@cindex @code{%}, quoting with @code{\} (backslash)
@cindex @code{\} (backslash), to quote @code{%}
@cindex backslash (@code{\}), to quote @code{%}
@cindex quoting @code{%}, in static pattern
@samp{%} characters in pattern rules can be quoted with preceding
backslashes (@samp{\}).  Backslashes that would otherwise quote @samp{%}
characters can be quoted with more backslashes.  Backslashes that quote
@samp{%} characters or other backslashes are removed from the pattern
before it is compared to file names or has a stem substituted into it.
Backslashes that are not in danger of quoting @samp{%} characters go
unmolested.  For example, the pattern @file{the\%weird\\%pattern\\} has
@samp{the%weird\} preceding the operative @samp{%} character, and
@samp{pattern\\} following it.  The final two backslashes are left alone
because they cannot affect any @samp{%} character.@refill

Here is an example, which compiles each of @file{foo.o} and @file{bar.o}
from the corresponding @file{.c} file:

@example
@group
objects = foo.o bar.o

all: $(objects)

$(objects): %.o: %.c
        $(CC) -c $(CFLAGS) $< -o $@@
@end group
@end example

@noindent
Here @samp{$<} is the automatic variable that holds the name of the
prerequisite and @samp{$@@} is the automatic variable that holds the name
of the target; see @ref{Automatic, , Automatic Variables}.

Each target specified must match the target pattern; a warning is issued
for each target that does not.  If you have a list of files, only some of
which will match the pattern, you can use the @code{filter} function to
remove nonmatching file names (@pxref{Text Functions, ,Functions for String Substitution and Analysis}):

@example
files = foo.elc bar.o lose.o

$(filter %.o,$(files)): %.o: %.c
        $(CC) -c $(CFLAGS) $< -o $@@
$(filter %.elc,$(files)): %.elc: %.el
        emacs -f batch-byte-compile $<
@end example

@noindent
In this example the result of @samp{$(filter %.o,$(files))} is
@file{bar.o lose.o}, and the first static pattern rule causes each of
these object files to be updated by compiling the corresponding C source
file.  The result of @w{@samp{$(filter %.elc,$(files))}} is
@file{foo.elc}, so that file is made from @file{foo.el}.@refill

Another example shows how to use @code{$*} in static pattern rules:
@vindex $*@r{, and static pattern}

@example
@group
bigoutput littleoutput : %output : text.g
        generate text.g -$* > $@@
@end group
@end example

@noindent
When the @code{generate} command is run, @code{$*} will expand to the
stem, either @samp{big} or @samp{little}.

@node Static versus Implicit,  , Static Usage, Static Pattern
@subsection Static Pattern Rules versus Implicit Rules
@cindex rule, static pattern versus implicit
@cindex static pattern rule, versus implicit

A static pattern rule has much in common with an implicit rule defined as a
pattern rule (@pxref{Pattern Rules, ,Defining and Redefining Pattern Rules}).
Both have a pattern for the target and patterns for constructing the
names of prerequisites.  The difference is in how @code{make} decides
@emph{when} the rule applies.

An implicit rule @emph{can} apply to any target that matches its pattern,
but it @emph{does} apply only when the target has no commands otherwise
specified, and only when the prerequisites can be found.  If more than one
implicit rule appears applicable, only one applies; the choice depends on
the order of rules.

By contrast, a static pattern rule applies to the precise list of targets
that you specify in the rule.  It cannot apply to any other target and it
invariably does apply to each of the targets specified.  If two conflicting
rules apply, and both have commands, that's an error.

The static pattern rule can be better than an implicit rule for these
reasons:

@itemize @bullet
@item
You may wish to override the usual implicit rule for a few
files whose names cannot be categorized syntactically but
can be given in an explicit list.

@item
If you cannot be sure of the precise contents of the directories
you are using, you may not be sure which other irrelevant files
might lead @code{make} to use the wrong implicit rule.  The choice
might depend on the order in which the implicit rule search is done.
With static pattern rules, there is no uncertainty: each rule applies
to precisely the targets specified.
@end itemize

@node Double-Colon, Automatic Prerequisites, Static Pattern, Rules
@section Double-Colon Rules
@cindex double-colon rules
@cindex rule, double-colon (@code{::})
@cindex multiple rules for one target (@code{::})
@cindex @code{::} rules (double-colon)

@dfn{Double-colon} rules are rules written with @samp{::} instead of
@samp{:} after the target names.  They are handled differently from
ordinary rules when the same target appears in more than one rule.

When a target appears in multiple rules, all the rules must be the same
type: all ordinary, or all double-colon.  If they are double-colon, each of
them is independent of the others.  Each double-colon rule's commands are
executed if the target is older than any prerequisites of that rule.  This
can result in executing none, any, or all of the double-colon rules.

Double-colon rules with the same target are in fact completely separate
from one another.  Each double-colon rule is processed individually, just
as rules with different targets are processed.

The double-colon rules for a target are executed in the order they appear
in the makefile.  However, the cases where double-colon rules really make
sense are those where the order of executing the commands would not matter.

Double-colon rules are somewhat obscure and not often very useful; they
provide a mechanism for cases in which the method used to update a target
differs depending on which prerequisite files caused the update, and such
cases are rare.

Each double-colon rule should specify commands; if it does not, an
implicit rule will be used if one applies.
@xref{Implicit Rules, ,Using Implicit Rules}.

@node Automatic Prerequisites,  , Double-Colon, Rules
@section Generating Prerequisites Automatically
@cindex prerequisites, automatic generation
@cindex automatic generation of prerequisites
@cindex generating prerequisites automatically

In the makefile for a program, many of the rules you need to write often
say only that some object file depends on some header
file.  For example, if @file{main.c} uses @file{defs.h} via an
@code{#include}, you would write:

@example
main.o: defs.h
@end example

@noindent
You need this rule so that @code{make} knows that it must remake
@file{main.o} whenever @file{defs.h} changes.  You can see that for a
large program you would have to write dozens of such rules in your
makefile.  And, you must always be very careful to update the makefile
every time you add or remove an @code{#include}.
@cindex @code{#include}

@cindex @code{-M} (to compiler)
To avoid this hassle, most modern C compilers can write these rules for
you, by looking at the @code{#include} lines in the source files.
Usually this is done with the @samp{-M} option to the compiler.
For example, the command:

@example
cc -M main.c
@end example

@noindent
generates the output:

@example
main.o : main.c defs.h
@end example

@noindent
Thus you no longer have to write all those rules yourself.
The compiler will do it for you.

Note that such a prerequisite constitutes mentioning @file{main.o} in a
makefile, so it can never be considered an intermediate file by implicit
rule search.  This means that @code{make} won't ever remove the file
after using it; @pxref{Chained Rules, ,Chains of Implicit Rules}.

@cindex @code{make depend}
With old @code{make} programs, it was traditional practice to use this
compiler feature to generate prerequisites on demand with a command like
@samp{make depend}.  That command would create a file @file{depend}
containing all the automatically-generated prerequisites; then the
makefile could use @code{include} to read them in (@pxref{Include}).

In GNU @code{make}, the feature of remaking makefiles makes this
practice obsolete---you need never tell @code{make} explicitly to
regenerate the prerequisites, because it always regenerates any makefile
that is out of date.  @xref{Remaking Makefiles}.

The practice we recommend for automatic prerequisite generation is to have
one makefile corresponding to each source file.  For each source file
@file{@var{name}.c} there is a makefile @file{@var{name}.d} which lists
what files the object file @file{@var{name}.o} depends on.  That way
only the source files that have changed need to be rescanned to produce
the new prerequisites.

Here is the pattern rule to generate a file of prerequisites (i.e., a makefile)
called @file{@var{name}.d} from a C source file called @file{@var{name}.c}:

@smallexample
@group
%.d: %.c
        set -e; $(CC) -M $(CPPFLAGS) $< \
                  | sed 's/\($*\)\.o[ :]*/\1.o $@@ : /g' > $@@; \
                [ -s $@@ ] || rm -f $@@
@end group
@end smallexample

@noindent
@xref{Pattern Rules}, for information on defining pattern rules.  The
@samp{-e} flag to the shell makes it exit immediately if the
@code{$(CC)} command fails (exits with a nonzero status).  Normally the
shell exits with the status of the last command in the pipeline
(@code{sed} in this case), so @code{make} would not notice a nonzero
status from the compiler.
@cindex @code{-e} (shell flag)

@cindex @code{-MM} (to GNU compiler)
With the GNU C compiler, you may wish to use the @samp{-MM} flag instead
of @samp{-M}.  This omits prerequisites on system header files.
@xref{Preprocessor Options, , Options Controlling the Preprocessor,
gcc.info, Using GNU CC}, for details.

@cindex @code{sed} (shell command)
The purpose of the @code{sed} command is to translate (for example):

@example
main.o : main.c defs.h
@end example

@noindent
into:

@example
main.o main.d : main.c defs.h
@end example

@noindent
@cindex @code{.d}
This makes each @samp{.d} file depend on all the source and header files
that the corresponding @samp{.o} file depends on.  @code{make} then
knows it must regenerate the prerequisites whenever any of the source or
header files changes.

Once you've defined the rule to remake the @samp{.d} files,
you then use the @code{include} directive to read them all in.
@xref{Include}.  For example:

@example
@group
sources = foo.c bar.c

include $(sources:.c=.d)
@end group
@end example

@noindent
(This example uses a substitution variable reference to translate the
list of source files @samp{foo.c bar.c} into a list of prerequisite
makefiles, @samp{foo.d bar.d}.  @xref{Substitution Refs}, for full
information on substitution references.)  Since the @samp{.d} files are
makefiles like any others, @code{make} will remake them as necessary
with no further work from you.  @xref{Remaking Makefiles}.

@node Commands, Using Variables, Rules, Top
@chapter Writing the Commands in Rules
@cindex commands, how to write
@cindex rule commands
@cindex writing rule commands

The commands of a rule consist of shell command lines to be executed one
by one.  Each command line must start with a tab, except that the first
command line may be attached to the target-and-prerequisites line with a
semicolon in between.  Blank lines and lines of just comments may appear
among the command lines; they are ignored.  (But beware, an apparently
``blank'' line that begins with a tab is @emph{not} blank!  It is an
empty command; @pxref{Empty Commands}.)

Users use many different shell programs, but commands in makefiles are
always interpreted by @file{/bin/sh} unless the makefile specifies
otherwise.  @xref{Execution, ,Command Execution}.

@cindex comments, in commands
@cindex commands, comments in
@cindex @code{#} (comments), in commands
The shell that is in use determines whether comments can be written on
command lines, and what syntax they use.  When the shell is
@file{/bin/sh}, a @samp{#} starts a comment that extends to the end of
the line.  The @samp{#} does not have to be at the beginning of a line.
Text on a line before a @samp{#} is not part of the comment.

@menu
* Echoing::                     How to control when commands are echoed.
* Execution::                   How commands are executed.
* Parallel::                    How commands can be executed in parallel.
* Errors::                      What happens after a command execution error.
* Interrupts::                  What happens when a command is interrupted.
* Recursion::                   Invoking @code{make} from makefiles.
* Sequences::                   Defining canned sequences of commands.
* Empty Commands::              Defining useful, do-nothing commands.
@end menu

@node Echoing, Execution,  , Commands
@section Command Echoing
@cindex echoing of commands
@cindex silent operation
@cindex @code{@@} (in commands)
@cindex commands, echoing
@cindex printing of commands

Normally @code{make} prints each command line before it is executed.
We call this @dfn{echoing} because it gives the appearance that you
are typing the commands yourself.

When a line starts with @samp{@@}, the echoing of that line is suppressed.
The @samp{@@} is discarded before the command is passed to the shell.
Typically you would use this for a command whose only effect is to print
something, such as an @code{echo} command to indicate progress through
the makefile:

@example
@@echo About to make distribution files
@end example

@cindex @code{-n}
@cindex @code{--just-print}
@cindex @code{--dry-run}
@cindex @code{--recon}
When @code{make} is given the flag @samp{-n} or @samp{--just-print}
it only echoes commands, it won't execute them.  @xref{Options Summary,
,Summary of Options}.  In this case and only this case, even the
commands starting with @samp{@@} are printed.  This flag is useful for
finding out which commands @code{make} thinks are necessary without
actually doing them.

@cindex @code{-s}
@cindex @code{--silent}
@cindex @code{--quiet}
@findex .SILENT
The @samp{-s} or @samp{--silent}
flag to @code{make} prevents all echoing, as if all commands
started with @samp{@@}.  A rule in the makefile for the special target
@code{.SILENT} without prerequisites has the same effect
(@pxref{Special Targets, ,Special Built-in Target Names}).
@code{.SILENT} is essentially obsolete since @samp{@@} is more flexible.@refill

@node Execution, Parallel, Echoing, Commands
@section Command Execution
@cindex commands, execution
@cindex execution, of commands
@cindex shell command, execution
@vindex SHELL @r{(command execution)}

When it is time to execute commands to update a target, they are executed
by making a new subshell for each line.  (In practice, @code{make} may
take shortcuts that do not affect the results.)

@cindex @code{cd} (shell command)
@strong{Please note:} this implies that shell commands such as @code{cd}
that set variables local to each process will not affect the following
command lines. @footnote{On MS-DOS, the value of current working
directory is @strong{global}, so changing it @emph{will} affect the
following command lines on those systems.}  If you want to use @code{cd}
to affect the next command, put the two on a single line with a
semicolon between them.  Then @code{make} will consider them a single
command and pass them, together, to a shell which will execute them in
sequence.  For example:

@example
foo : bar/lose
        cd bar; gobble lose > ../foo
@end example

@cindex commands, backslash (@code{\}) in
@cindex commands, quoting newlines in
@cindex backslash (@code{\}), in commands
@cindex @code{\} (backslash), in commands
@cindex quoting newline, in commands
@cindex newline, quoting, in commands
If you would like to split a single shell command into multiple lines of
text, you must use a backslash at the end of all but the last subline.
Such a sequence of lines is combined into a single line, by deleting the
backslash-newline sequences, before passing it to the shell.  Thus, the
following is equivalent to the preceding example:

@example
@group
foo : bar/lose
        cd bar;  \
        gobble lose > ../foo
@end group
@end example

@vindex SHELL
The program used as the shell is taken from the variable @code{SHELL}.
By default, the program @file{/bin/sh} is used.

@vindex COMSPEC
On MS-DOS, if @code{SHELL} is not set, the value of the variable
@code{COMSPEC} (which is always set) is used instead.

@cindex @code{SHELL}, MS-DOS specifics
The processing of lines that set the variable @code{SHELL} in Makefiles
is different on MS-DOS.  The stock shell, @file{command.com}, is
ridiculously limited in its functionality and many users of @code{make}
tend to install a replacement shell.  Therefore, on MS-DOS, @code{make}
examines the value of @code{SHELL}, and changes its behavior based on
whether it points to a Unix-style or DOS-style shell.  This allows
reasonable functionality even if @code{SHELL} points to
@file{command.com}.

If @code{SHELL} points to a Unix-style shell, @code{make} on MS-DOS
additionally checks whether that shell can indeed be found; if not, it
ignores the line that sets @code{SHELL}.  In MS-DOS, GNU @code{make}
searches for the shell in the following places:

@enumerate
@item
In the precise place pointed to by the value of @code{SHELL}.  For
example, if the makefile specifies @samp{SHELL = /bin/sh}, @code{make}
will look in the directory @file{/bin} on the current drive.

@item
In the current directory.

@item
In each of the directories in the @code{PATH} variable, in order.

@end enumerate

In every directory it examines, @code{make} will first look for the
specific file (@file{sh} in the example above).  If this is not found,
it will also look in that directory for that file with one of the known
extensions which identify executable files.  For example @file{.exe},
@file{.com}, @file{.bat}, @file{.btm}, @file{.sh}, and some others.

If any of these attempts is successful, the value of @code{SHELL} will
be set to the full pathname of the shell as found.  However, if none of
these is found, the value of @code{SHELL} will not be changed, and thus
the line that sets it will be effectively ignored.  This is so
@code{make} will only support features specific to a Unix-style shell if
such a shell is actually installed on the system where @code{make} runs.

Note that this extended search for the shell is limited to the cases
where @code{SHELL} is set from the Makefile; if it is set in the
environment or command line, you are expected to set it to the full
pathname of the shell, exactly as things are on Unix.

The effect of the above DOS-specific processing is that a Makefile that
says @samp{SHELL = /bin/sh} (as many Unix makefiles do), will work
on MS-DOS unaltered if you have e.g. @file{sh.exe} installed in some
directory along your @code{PATH}.

@cindex environment, @code{SHELL} in
Unlike most variables, the variable @code{SHELL} is never set from the
environment.  This is because the @code{SHELL} environment variable is
used to specify your personal choice of shell program for interactive
use.  It would be very bad for personal choices like this to affect the
functioning of makefiles.  @xref{Environment, ,Variables from the
Environment}.  However, on MS-DOS and MS-Windows the value of
@code{SHELL} in the environment @strong{is} used, since on those systems
most users do not set this variable, and therefore it is most likely set
specifically to be used by @code{make}.  On MS-DOS, if the setting of
@code{SHELL} is not suitable for @code{make}, you can set the variable
@code{MAKESHELL} to the shell that @code{make} should use; this will
override the value of @code{SHELL}.

@node Parallel, Errors, Execution, Commands
@section Parallel Execution
@cindex commands, execution in parallel
@cindex parallel execution
@cindex execution, in parallel
@cindex job slots
@cindex @code{-j}
@cindex @code{--jobs}

GNU @code{make} knows how to execute several commands at once.
Normally, @code{make} will execute only one command at a time, waiting
for it to finish before executing the next.  However, the @samp{-j} or
@samp{--jobs} option tells @code{make} to execute many commands
simultaneously.@refill

On MS-DOS, the @samp{-j} option has no effect, since that system doesn't
support multi-processing.

If the @samp{-j} option is followed by an integer, this is the number of
commands to execute at once; this is called the number of @dfn{job slots}.
If there is nothing looking like an integer after the @samp{-j} option,
there is no limit on the number of job slots.  The default number of job
slots is one, which means serial execution (one thing at a time).

One unpleasant consequence of running several commands simultaneously is
that output generated by the commands appears whenever each command
sends it, so messages from different commands may be interspersed.

Another problem is that two processes cannot both take input from the
same device; so to make sure that only one command tries to take input
from the terminal at once, @code{make} will invalidate the standard
input streams of all but one running command.  This means that
attempting to read from standard input will usually be a fatal error (a
@samp{Broken pipe} signal) for most child processes if there are
several.
@cindex broken pipe
@cindex standard input

It is unpredictable which command will have a valid standard input stream
(which will come from the terminal, or wherever you redirect the standard
input of @code{make}).  The first command run will always get it first, and
the first command started after that one finishes will get it next, and so
on.

We will change how this aspect of @code{make} works if we find a better
alternative.  In the mean time, you should not rely on any command using
standard input at all if you are using the parallel execution feature; but
if you are not using this feature, then standard input works normally in
all commands.

Finally, handling recursive @code{make} invocations raises issues.  For
more information on this, see
@ref{Options/Recursion, ,Communicating Options to a Sub-@code{make}}.

If a command fails (is killed by a signal or exits with a nonzero
status), and errors are not ignored for that command
(@pxref{Errors, ,Errors in Commands}),
the remaining command lines to remake the same target will not be run.
If a command fails and the @samp{-k} or @samp{--keep-going}
option was not given
(@pxref{Options Summary, ,Summary of Options}),
@code{make} aborts execution.  If make
terminates for any reason (including a signal) with child processes
running, it waits for them to finish before actually exiting.@refill

@cindex load average
@cindex limiting jobs based on load
@cindex jobs, limiting based on load
@cindex @code{-l} (load average)
@cindex @code{--max-load}
@cindex @code{--load-average}
When the system is heavily loaded, you will probably want to run fewer jobs
than when it is lightly loaded.  You can use the @samp{-l} option to tell
@code{make} to limit the number of jobs to run at once, based on the load
average.  The @samp{-l} or @samp{--max-load}
option is followed by a floating-point number.  For
example,

@example
-l 2.5
@end example

@noindent
will not let @code{make} start more than one job if the load average is
above 2.5.  The @samp{-l} option with no following number removes the
load limit, if one was given with a previous @samp{-l} option.@refill

More precisely, when @code{make} goes to start up a job, and it already has
at least one job running, it checks the current load average; if it is not
lower than the limit given with @samp{-l}, @code{make} waits until the load
average goes below that limit, or until all the other jobs finish.

By default, there is no load limit.

@node Errors, Interrupts, Parallel, Commands
@section Errors in Commands
@cindex errors (in commands)
@cindex commands, errors in
@cindex exit status (errors)

After each shell command returns, @code{make} looks at its exit status.
If the command completed successfully, the next command line is executed
in a new shell; after the last command line is finished, the rule is
finished.

If there is an error (the exit status is nonzero), @code{make} gives up on
the current rule, and perhaps on all rules.

Sometimes the failure of a certain command does not indicate a problem.
For example, you may use the @code{mkdir} command to ensure that a
directory exists.  If the directory already exists, @code{mkdir} will
report an error, but you probably want @code{make} to continue regardless.

@cindex @code{-} (in commands)
To ignore errors in a command line, write a @samp{-} at the beginning of
the line's text (after the initial tab).  The @samp{-} is discarded before
the command is passed to the shell for execution.

For example,

@example
@group
clean:
        -rm -f *.o
@end group
@end example
@cindex @code{rm} (shell command)

@noindent
This causes @code{rm} to continue even if it is unable to remove a file.

@cindex @code{-i}
@cindex @code{--ignore-errors}
@findex .IGNORE
When you run @code{make} with the @samp{-i} or @samp{--ignore-errors}
flag, errors are ignored in all commands of all rules.  A rule in the
makefile for the special target @code{.IGNORE} has the same effect, if
there are no prerequisites.  These ways of ignoring errors are obsolete
because @samp{-} is more flexible.

When errors are to be ignored, because of either a @samp{-} or the
@samp{-i} flag, @code{make} treats an error return just like success,
except that it prints out a message that tells you the status code
the command exited with, and says that the error has been ignored.

When an error happens that @code{make} has not been told to ignore,
it implies that the current target cannot be correctly remade, and neither
can any other that depends on it either directly or indirectly.  No further
commands will be executed for these targets, since their preconditions
have not been achieved.


@cindex @code{-k}
@cindex @code{--keep-going}
Normally @code{make} gives up immediately in this circumstance, returning a
nonzero status.  However, if the @samp{-k} or @samp{--keep-going}
flag is specified, @code{make}
continues to consider the other prerequisites of the pending targets,
remaking them if necessary, before it gives up and returns nonzero status.
For example, after an error in compiling one object file, @samp{make -k}
will continue compiling other object files even though it already knows
that linking them will be impossible.  @xref{Options Summary, ,Summary of Options}.

The usual behavior assumes that your purpose is to get the specified
targets up to date; once @code{make} learns that this is impossible, it
might as well report the failure immediately.  The @samp{-k} option says
that the real purpose is to test as many of the changes made in the
program as possible, perhaps to find several independent problems so
that you can correct them all before the next attempt to compile.  This
is why Emacs' @code{compile} command passes the @samp{-k} flag by
default.
@cindex Emacs (@code{M-x compile})

@findex .DELETE_ON_ERROR
@cindex deletion of target files
@cindex removal of target files
@cindex target, deleting on error
Usually when a command fails, if it has changed the target file at all,
the file is corrupted and cannot be used---or at least it is not
completely updated.  Yet the file's timestamp says that it is now up to
date, so the next time @code{make} runs, it will not try to update that
file.  The situation is just the same as when the command is killed by a
signal; @pxref{Interrupts}.  So generally the right thing to do is to
delete the target file if the command fails after beginning to change
the file.  @code{make} will do this if @code{.DELETE_ON_ERROR} appears
as a target.  This is almost always what you want @code{make} to do, but
it is not historical practice; so for compatibility, you must explicitly
request it.

@node Interrupts, Recursion, Errors, Commands
@section Interrupting or Killing @code{make}
@cindex interrupt
@cindex signal
@cindex deletion of target files
@cindex removal of target files
@cindex target, deleting on interrupt
@cindex killing (interruption)

If @code{make} gets a fatal signal while a command is executing, it may
delete the target file that the command was supposed to update.  This is
done if the target file's last-modification time has changed since
@code{make} first checked it.

The purpose of deleting the target is to make sure that it is remade from
scratch when @code{make} is next run.  Why is this?  Suppose you type
@kbd{Ctrl-c} while a compiler is running, and it has begun to write an
object file @file{foo.o}.  The @kbd{Ctrl-c} kills the compiler, resulting
in an incomplete file whose last-modification time is newer than the source
file @file{foo.c}.  But @code{make} also receives the @kbd{Ctrl-c} signal
and deletes this incomplete file.  If @code{make} did not do this, the next
invocation of @code{make} would think that @file{foo.o} did not require
updating---resulting in a strange error message from the linker when it
tries to link an object file half of which is missing.

@findex .PRECIOUS
You can prevent the deletion of a target file in this way by making the
special target @code{.PRECIOUS} depend on it.  Before remaking a target,
@code{make} checks to see whether it appears on the prerequisites of
@code{.PRECIOUS}, and thereby decides whether the target should be deleted
if a signal happens.  Some reasons why you might do this are that the
target is updated in some atomic fashion, or exists only to record a
modification-time (its contents do not matter), or must exist at all
times to prevent other sorts of trouble.

@node Recursion, Sequences, Interrupts, Commands
@section Recursive Use of @code{make}
@cindex recursion
@cindex subdirectories, recursion for

Recursive use of @code{make} means using @code{make} as a command in a
makefile.  This technique is useful when you want separate makefiles for
various subsystems that compose a larger system.  For example, suppose you
have a subdirectory @file{subdir} which has its own makefile, and you would
like the containing directory's makefile to run @code{make} on the
subdirectory.  You can do it by writing this:

@example
subsystem:
        cd subdir && $(MAKE)
@end example

@noindent
or, equivalently, this (@pxref{Options Summary, ,Summary of Options}):

@example
subsystem:
        $(MAKE) -C subdir
@end example
@cindex @code{-C}
@cindex @code{--directory}

You can write recursive @code{make} commands just by copying this example,
but there are many things to know about how they work and why, and about
how the sub-@code{make} relates to the top-level @code{make}.

For your convenience, GNU @code{make} sets the variable @code{CURDIR} to
the pathname of the current working directory for you.  If @code{-C} is
in effect, it will contain the path of the new directory, not the
original.  The value has the same precedence it would have if it were
set in the makefile (by default, an environment variable @code{CURDIR}
will not override this value).  Note that setting this variable has no
effect on the operation of @code{make}

@menu
* MAKE Variable::               The special effects of using @samp{$(MAKE)}.
* Variables/Recursion::         How to communicate variables to a sub-@code{make}.
* Options/Recursion::           How to communicate options to a sub-@code{make}.
* -w Option::                   How the @samp{-w} or @samp{--print-directory} option
                                 helps debug use of recursive @code{make} commands.
@end menu

@node MAKE Variable, Variables/Recursion,  , Recursion
@subsection How the @code{MAKE} Variable Works
@vindex MAKE
@cindex recursion, and @code{MAKE} variable

Recursive @code{make} commands should always use the variable @code{MAKE},
not the explicit command name @samp{make}, as shown here:

@example
@group
subsystem:
        cd subdir && $(MAKE)
@end group
@end example

The value of this variable is the file name with which @code{make} was
invoked.  If this file name was @file{/bin/make}, then the command executed
is @samp{cd subdir && /bin/make}.  If you use a special version of
@code{make} to run the top-level makefile, the same special version will be
executed for recursive invocations.
@cindex @code{cd} (shell command)

As a special feature, using the variable @code{MAKE} in the commands of
a rule alters the effects of the @samp{-t} (@samp{--touch}), @samp{-n}
(@samp{--just-print}), or @samp{-q} (@w{@samp{--question}}) option.
Using the @code{MAKE} variable has the same effect as using a @samp{+}
character at the beginning of the command line.  @xref{Instead of
Execution, ,Instead of Executing the Commands}.@refill

Consider the command @samp{make -t} in the above example.  (The
@samp{-t} option marks targets as up to date without actually running
any commands; see @ref{Instead of Execution}.)  Following the usual
definition of @samp{-t}, a @samp{make -t} command in the example would
create a file named @file{subsystem} and do nothing else.  What you
really want it to do is run @samp{@w{cd subdir &&} @w{make -t}}; but that would
require executing the command, and @samp{-t} says not to execute
commands.@refill
@cindex @code{-t}, and recursion
@cindex recursion, and @code{-t}
@cindex @code{--touch}, and recursion

The special feature makes this do what you want: whenever a command
line of a rule contains the variable @code{MAKE}, the flags @samp{-t},
@samp{-n} and @samp{-q} do not apply to that line.  Command lines
containing @code{MAKE} are executed normally despite the presence of a
flag that causes most commands not to be run.  The usual
@code{MAKEFLAGS} mechanism passes the flags to the sub-@code{make}
(@pxref{Options/Recursion, ,Communicating Options to a
Sub-@code{make}}), so your request to touch the files, or print the
commands, is propagated to the subsystem.@refill

@node Variables/Recursion, Options/Recursion, MAKE Variable, Recursion
@subsection Communicating Variables to a Sub-@code{make}
@cindex sub-@code{make}
@cindex environment, and recursion
@cindex exporting variables
@cindex variables, environment
@cindex variables, exporting
@cindex recursion, and environment
@cindex recursion, and variables

Variable values of the top-level @code{make} can be passed to the
sub-@code{make} through the environment by explicit request.  These
variables are defined in the sub-@code{make} as defaults, but do not
override what is specified in the makefile used by the sub-@code{make}
makefile unless you use the @samp{-e} switch (@pxref{Options Summary,
,Summary of Options}).@refill

To pass down, or @dfn{export}, a variable, @code{make} adds the variable
and its value to the environment for running each command.  The
sub-@code{make}, in turn, uses the environment to initialize its table
of variable values.  @xref{Environment, ,Variables from the
Environment}.

Except by explicit request, @code{make} exports a variable only if it
is either defined in the environment initially or set on the command
line, and if its name consists only of letters, numbers, and underscores.
Some shells cannot cope with environment variable names consisting of
characters other than letters, numbers, and underscores.

The special variables @code{SHELL} and @code{MAKEFLAGS} are always
exported (unless you unexport them).
@code{MAKEFILES} is exported if you set it to anything.

@code{make} automatically passes down variable values that were defined
on the command line, by putting them in the @code{MAKEFLAGS} variable.
@iftex
See the next section.
@end iftex
@ifinfo
@xref{Options/Recursion}.
@end ifinfo

Variables are @emph{not} normally passed down if they were created by
default by @code{make} (@pxref{Implicit Variables, ,Variables Used by
Implicit Rules}).  The sub-@code{make} will define these for
itself.@refill

@findex export
If you want to export specific variables to a sub-@code{make}, use the
@code{export} directive, like this:

@example
export @var{variable} @dots{}
@end example

@noindent
@findex unexport
If you want to @emph{prevent} a variable from being exported, use the
@code{unexport} directive, like this:

@example
unexport @var{variable} @dots{}
@end example

@noindent
As a convenience, you can define a variable and export it at the same
time by doing:

@example
export @var{variable} = value
@end example

@noindent
has the same result as:

@example
@var{variable} = value
export @var{variable}
@end example

@noindent
and

@example
export @var{variable} := value
@end example

@noindent
has the same result as:

@example
@var{variable} := value
export @var{variable}
@end example

Likewise,

@example
export @var{variable} += value
@end example

@noindent
is just like:

@example
@var{variable} += value
export @var{variable}
@end example

@noindent
@xref{Appending, ,Appending More Text to Variables}.

You may notice that the @code{export} and @code{unexport} directives
work in @code{make} in the same way they work in the shell, @code{sh}.

If you want all variables to be exported by default, you can use
@code{export} by itself:

@example
export
@end example

@noindent
This tells @code{make} that variables which are not explicitly mentioned
in an @code{export} or @code{unexport} directive should be exported.
Any variable given in an @code{unexport} directive will still @emph{not}
be exported.  If you use @code{export} by itself to export variables by
default, variables whose names contain characters other than
alphanumerics and underscores will not be exported unless specifically
mentioned in an @code{export} directive.@refill

@findex .EXPORT_ALL_VARIABLES
The behavior elicited by an @code{export} directive by itself was the
default in older versions of GNU @code{make}.  If your makefiles depend
on this behavior and you want to be compatible with old versions of
@code{make}, you can write a rule for the special target
@code{.EXPORT_ALL_VARIABLES} instead of using the @code{export} directive.
This will be ignored by old @code{make}s, while the @code{export}
directive will cause a syntax error.@refill
@cindex compatibility in exporting

Likewise, you can use @code{unexport} by itself to tell @code{make}
@emph{not} to export variables by default.  Since this is the default
behavior, you would only need to do this if @code{export} had been used
by itself earlier (in an included makefile, perhaps).  You
@strong{cannot} use @code{export} and @code{unexport} by themselves to
have variables exported for some commands and not for others.  The last
@code{export} or @code{unexport} directive that appears by itself
determines the behavior for the entire run of @code{make}.@refill

@vindex MAKELEVEL
@cindex recursion, level of
As a special feature, the variable @code{MAKELEVEL} is changed when it
is passed down from level to level.  This variable's value is a string
which is the depth of the level as a decimal number.  The value is
@samp{0} for the top-level @code{make}; @samp{1} for a sub-@code{make},
@samp{2} for a sub-sub-@code{make}, and so on.  The incrementation
happens when @code{make} sets up the environment for a command.@refill

The main use of @code{MAKELEVEL} is to test it in a conditional
directive (@pxref{Conditionals, ,Conditional Parts of Makefiles}); this
way you can write a makefile that behaves one way if run recursively and
another way if run directly by you.@refill

@vindex MAKEFILES
You can use the variable @code{MAKEFILES} to cause all sub-@code{make}
commands to use additional makefiles.  The value of @code{MAKEFILES} is
a whitespace-separated list of file names.  This variable, if defined in
the outer-level makefile, is passed down through the environment; then
it serves as a list of extra makefiles for the sub-@code{make} to read
before the usual or specified ones.  @xref{MAKEFILES Variable, ,The
Variable @code{MAKEFILES}}.@refill

@node Options/Recursion, -w Option, Variables/Recursion, Recursion
@subsection Communicating Options to a Sub-@code{make}
@cindex options, and recursion
@cindex recursion, and options

@vindex MAKEFLAGS
Flags such as @samp{-s} and @samp{-k} are passed automatically to the
sub-@code{make} through the variable @code{MAKEFLAGS}.  This variable is
set up automatically by @code{make} to contain the flag letters that
@code{make} received.  Thus, if you do @w{@samp{make -ks}} then
@code{MAKEFLAGS} gets the value @samp{ks}.@refill

As a consequence, every sub-@code{make} gets a value for @code{MAKEFLAGS}
in its environment.  In response, it takes the flags from that value and
processes them as if they had been given as arguments.
@xref{Options Summary, ,Summary of Options}.

@cindex command line variable definitions, and recursion
@cindex variables, command line, and recursion
@cindex recursion, and command line variable definitions
Likewise variables defined on the command line are passed to the
sub-@code{make} through @code{MAKEFLAGS}.  Words in the value of
@code{MAKEFLAGS} that contain @samp{=}, @code{make} treats as variable
definitions just as if they appeared on the command line.
@xref{Overriding, ,Overriding Variables}.

@cindex @code{-C}, and recursion
@cindex @code{-f}, and recursion
@cindex @code{-o}, and recursion
@cindex @code{-W}, and recursion
@cindex @code{--directory}, and recursion
@cindex @code{--file}, and recursion
@cindex @code{--old-file}, and recursion
@cindex @code{--assume-old}, and recursion
@cindex @code{--assume-new}, and recursion
@cindex @code{--new-file}, and recursion
@cindex recursion, and @code{-C}
@cindex recursion, and @code{-f}
@cindex recursion, and @code{-o}
@cindex recursion, and @code{-W}
The options @samp{-C}, @samp{-f}, @samp{-o}, and @samp{-W} are not put
into @code{MAKEFLAGS}; these options are not passed down.@refill

@cindex @code{-j}, and recursion
@cindex @code{--jobs}, and recursion
@cindex recursion, and @code{-j}
@cindex job slots, and recursion
The @samp{-j} option is a special case (@pxref{Parallel, ,Parallel Execution}).
If you set it to some numeric value @samp{N} and your operating system
supports it (most any UNIX system will; others typically won't), the
parent @code{make} and all the sub-@code{make}s will communicate to
ensure that there are only @samp{N} jobs running at the same time
between them all.  Note that any job that is marked recursive
(@pxref{Instead of Execution, ,Instead of Executing the Commands})
doesn't count against the total jobs (otherwise we could get @samp{N}
sub-@code{make}s running and have no slots left over for any real work!)

If your operating system doesn't support the above communication, then
@samp{-j 1} is always put into @code{MAKEFLAGS} instead of the value you
specified.  This is because if the @w{@samp{-j}} option were passed down
to sub-@code{make}s, you would get many more jobs running in parallel
than you asked for.  If you give @samp{-j} with no numeric argument,
meaning to run as many jobs as possible in parallel, this is passed
down, since multiple infinities are no more than one.@refill

If you do not want to pass the other flags down, you must change the
value of @code{MAKEFLAGS}, like this:

@example
subsystem:
        cd subdir && $(MAKE) MAKEFLAGS=
@end example

@vindex MAKEOVERRIDES
The command line variable definitions really appear in the variable
@code{MAKEOVERRIDES}, and @code{MAKEFLAGS} contains a reference to this
variable.  If you do want to pass flags down normally, but don't want to
pass down the command line variable definitions, you can reset
@code{MAKEOVERRIDES} to empty, like this:

@example
MAKEOVERRIDES =
@end example

@noindent
@cindex Arg list too long
@cindex E2BIG
This is not usually useful to do.  However, some systems have a small
fixed limit on the size of the environment, and putting so much
information into the value of @code{MAKEFLAGS} can exceed it.  If you
see the error message @samp{Arg list too long}, this may be the problem.
@findex .POSIX
@cindex POSIX.2
(For strict compliance with POSIX.2, changing @code{MAKEOVERRIDES} does
not affect @code{MAKEFLAGS} if the special target @samp{.POSIX} appears
in the makefile.  You probably do not care about this.)

@vindex MFLAGS
A similar variable @code{MFLAGS} exists also, for historical
compatibility.  It has the same value as @code{MAKEFLAGS} except that it
does not contain the command line variable definitions, and it always
begins with a hyphen unless it is empty (@code{MAKEFLAGS} begins with a
hyphen only when it begins with an option that has no single-letter
version, such as @samp{--warn-undefined-variables}).  @code{MFLAGS} was
traditionally used explicitly in the recursive @code{make} command, like
this:

@example
subsystem:
        cd subdir && $(MAKE) $(MFLAGS)
@end example

@noindent
but now @code{MAKEFLAGS} makes this usage redundant.  If you want your
makefiles to be compatible with old @code{make} programs, use this
technique; it will work fine with more modern @code{make} versions too.

@cindex setting options from environment
@cindex options, setting from environment
@cindex setting options in makefiles
@cindex options, setting in makefiles
The @code{MAKEFLAGS} variable can also be useful if you want to have
certain options, such as @samp{-k} (@pxref{Options Summary, ,Summary of
Options}), set each time you run @code{make}.  You simply put a value for
@code{MAKEFLAGS} in your environment.  You can also set @code{MAKEFLAGS} in
a makefile, to specify additional flags that should also be in effect for
that makefile.  (Note that you cannot use @code{MFLAGS} this way.  That
variable is set only for compatibility; @code{make} does not interpret a
value you set for it in any way.)

When @code{make} interprets the value of @code{MAKEFLAGS} (either from the
environment or from a makefile), it first prepends a hyphen if the value
does not already begin with one.  Then it chops the value into words
separated by blanks, and parses these words as if they were options given
on the command line (except that @samp{-C}, @samp{-f}, @samp{-h},
@samp{-o}, @samp{-W}, and their long-named versions are ignored; and there
is no error for an invalid option).

If you do put @code{MAKEFLAGS} in your environment, you should be sure not
to include any options that will drastically affect the actions of
@code{make} and undermine the purpose of makefiles and of @code{make}
itself.  For instance, the @samp{-t}, @samp{-n}, and @samp{-q} options, if
put in one of these variables, could have disastrous consequences and would
certainly have at least surprising and probably annoying effects.@refill

@node -w Option,  , Options/Recursion, Recursion
@subsection The @samp{--print-directory} Option
@cindex directories, printing them
@cindex printing directories
@cindex recursion, and printing directories

If you use several levels of recursive @code{make} invocations, the
@samp{-w} or @w{@samp{--print-directory}} option can make the output a
lot easier to understand by showing each directory as @code{make}
starts processing it and as @code{make} finishes processing it.  For
example, if @samp{make -w} is run in the directory @file{/u/gnu/make},
@code{make} will print a line of the form:@refill

@example
make: Entering directory `/u/gnu/make'.
@end example

@noindent
before doing anything else, and a line of the form:

@example
make: Leaving directory `/u/gnu/make'.
@end example

@noindent
when processing is completed.

@cindex @code{-C}, and @code{-w}
@cindex @code{--directory}, and @code{--print-directory}
@cindex recursion, and @code{-w}
@cindex @code{-w}, and @code{-C}
@cindex @code{-w}, and recursion
@cindex @code{--print-directory}, and @code{--directory}
@cindex @code{--print-directory}, and recursion
@cindex @code{--no-print-directory}
@cindex @code{--print-directory}, disabling
@cindex @code{-w}, disabling
Normally, you do not need to specify this option because @samp{make}
does it for you: @samp{-w} is turned on automatically when you use the
@samp{-C} option, and in sub-@code{make}s.  @code{make} will not
automatically turn on @samp{-w} if you also use @samp{-s}, which says to
be silent, or if you use @samp{--no-print-directory} to explicitly
disable it.

@node Sequences, Empty Commands, Recursion, Commands
@section Defining Canned Command Sequences
@cindex sequences of commands
@cindex commands, sequences of

When the same sequence of commands is useful in making various targets, you
can define it as a canned sequence with the @code{define} directive, and
refer to the canned sequence from the rules for those targets.  The canned
sequence is actually a variable, so the name must not conflict with other
variable names.

Here is an example of defining a canned sequence of commands:

@example
define run-yacc
yacc $(firstword $^)
mv y.tab.c $@@
endef
@end example
@cindex @code{yacc}

@noindent
Here @code{run-yacc} is the name of the variable being defined;
@code{endef} marks the end of the definition; the lines in between are the
commands.  The @code{define} directive does not expand variable references
and function calls in the canned sequence; the @samp{$} characters,
parentheses, variable names, and so on, all become part of the value of the
variable you are defining.
@xref{Defining, ,Defining Variables Verbatim},
for a complete explanation of @code{define}.

The first command in this example runs Yacc on the first prerequisite of
whichever rule uses the canned sequence.  The output file from Yacc is
always named @file{y.tab.c}.  The second command moves the output to the
rule's target file name.

To use the canned sequence, substitute the variable into the commands of a
rule.  You can substitute it like any other variable
(@pxref{Reference, ,Basics of Variable References}).
Because variables defined by @code{define} are recursively expanded
variables, all the variable references you wrote inside the @code{define}
are expanded now.  For example:

@example
foo.c : foo.y
        $(run-yacc)
@end example

@noindent
@samp{foo.y} will be substituted for the variable @samp{$^} when it occurs in
@code{run-yacc}'s value, and @samp{foo.c} for @samp{$@@}.@refill

This is a realistic example, but this particular one is not needed in
practice because @code{make} has an implicit rule to figure out these
commands based on the file names involved
(@pxref{Implicit Rules, ,Using Implicit Rules}).

@cindex @@, and @code{define}
@cindex -, and @code{define}
@cindex +, and @code{define}
In command execution, each line of a canned sequence is treated just as
if the line appeared on its own in the rule, preceded by a tab.  In
particular, @code{make} invokes a separate subshell for each line.  You
can use the special prefix characters that affect command lines
(@samp{@@}, @samp{-}, and @samp{+}) on each line of a canned sequence.
@xref{Commands, ,Writing the Commands in Rules}.
For example, using this canned sequence:

@example
define frobnicate
@@echo "frobnicating target $@@"
frob-step-1 $< -o $@@-step-1
frob-step-2 $@@-step-1 -o $@@
endef
@end example

@noindent
@code{make} will not echo the first line, the @code{echo} command.
But it @emph{will} echo the following two command lines.

On the other hand, prefix characters on the command line that refers to
a canned sequence apply to every line in the sequence.  So the rule:

@example
frob.out: frob.in
        @@$(frobnicate)
@end example

@noindent
does not echo @emph{any} commands.
(@xref{Echoing, ,Command Echoing}, for a full explanation of @samp{@@}.)

@node Empty Commands,  , Sequences, Commands
@section Using Empty Commands
@cindex empty commands
@cindex commands, empty

It is sometimes useful to define commands which do nothing.  This is done
simply by giving a command that consists of nothing but whitespace.  For
example:

@example
target: ;
@end example

@noindent
defines an empty command string for @file{target}.  You could also use a
line beginning with a tab character to define an empty command string,
but this would be confusing because such a line looks empty.

@findex .DEFAULT@r{, and empty commands}
You may be wondering why you would want to define a command string that
does nothing.  The only reason this is useful is to prevent a target
from getting implicit commands (from implicit rules or the
@code{.DEFAULT} special target; @pxref{Implicit Rules} and
@pxref{Last Resort, ,Defining Last-Resort Default Rules}).@refill

@c !!! another reason is for canonical stamp files:
@ignore
foo: stamp-foo ;
stamp-foo: foo.in
        create foo frm foo.in
        touch $@
@end ignore

You may be inclined to define empty command strings for targets that are
not actual files, but only exist so that their prerequisites can be
remade.  However, this is not the best way to do that, because the
prerequisites may not be remade properly if the target file actually does exist.
@xref{Phony Targets, ,Phony Targets}, for a better way to do this.

@node Using Variables, Conditionals, Commands, Top
@chapter How to Use Variables
@cindex variable
@cindex value
@cindex recursive variable expansion
@cindex simple variable expansion

A @dfn{variable} is a name defined in a makefile to represent a string
of text, called the variable's @dfn{value}.  These values are
substituted by explicit request into targets, prerequisites, commands,
and other parts of the makefile.  (In some other versions of @code{make},
variables are called @dfn{macros}.)
@cindex macro

Variables and functions in all parts of a makefile are expanded when
read, except for the shell commands in rules, the right-hand sides of
variable definitions using @samp{=}, and the bodies of variable
definitions using the @code{define} directive.@refill

Variables can represent lists of file names, options to pass to compilers,
programs to run, directories to look in for source files, directories to
write output in, or anything else you can imagine.

A variable name may be any sequence of characters not containing @samp{:},
@samp{#}, @samp{=}, or leading or trailing whitespace.  However,
variable names containing characters other than letters, numbers, and
underscores should be avoided, as they may be given special meanings in the
future, and with some shells they cannot be passed through the environment to a
sub-@code{make}
(@pxref{Variables/Recursion, ,Communicating Variables to a Sub-@code{make}}).

Variable names are case-sensitive.  The names @samp{foo}, @samp{FOO},
and @samp{Foo} all refer to different variables.

It is traditional to use upper case letters in variable names, but we
recommend using lower case letters for variable names that serve internal
purposes in the makefile, and reserving upper case for parameters that
control implicit rules or for parameters that the user should override with
command options (@pxref{Overriding, ,Overriding Variables}).

A few variables have names that are a single punctuation character or
just a few characters.  These are the @dfn{automatic variables}, and
they have particular specialized uses.  @xref{Automatic, ,Automatic Variables}.

@menu
* Reference::                   How to use the value of a variable.
* Flavors::                     Variables come in two flavors.
* Advanced::                    Advanced features for referencing a variable.
* Values::                      All the ways variables get their values.
* Setting::                     How to set a variable in the makefile.
* Appending::                   How to append more text to the old value
                                  of a variable.
* Override Directive::          How to set a variable in the makefile even if
                                  the user has set it with a command argument.
* Defining::                    An alternate way to set a variable
                                  to a verbatim string.
* Environment::                 Variable values can come from the environment.
* Target-specific::             Variable values can be defined on a per-target
                                  basis.
* Pattern-specific::            Target-specific variable values can be applied
                                  to a group of targets that match a pattern.
* Automatic::                   Some special variables have predefined
                                  meanings for use with implicit rules.
@end menu

@node Reference, Flavors,  , Using Variables
@section Basics of Variable References
@cindex variables, how to reference
@cindex reference to variables
@cindex @code{$}, in variable reference
@cindex dollar sign (@code{$}), in variable reference

To substitute a variable's value, write a dollar sign followed by the name
of the variable in parentheses or braces: either @samp{$(foo)} or
@samp{$@{foo@}} is a valid reference to the variable @code{foo}.  This
special significance of @samp{$} is why you must write @samp{$$} to have
the effect of a single dollar sign in a file name or command.

Variable references can be used in any context: targets, prerequisites,
commands, most directives, and new variable values.  Here is an
example of a common case, where a variable holds the names of all the
object files in a program:

@example
@group
objects = program.o foo.o utils.o
program : $(objects)
        cc -o program $(objects)

$(objects) : defs.h
@end group
@end example

Variable references work by strict textual substitution.  Thus, the rule

@example
@group
foo = c
prog.o : prog.$(foo)
        $(foo)$(foo) -$(foo) prog.$(foo)
@end group
@end example

@noindent
could be used to compile a C program @file{prog.c}.  Since spaces before
the variable value are ignored in variable assignments, the value of
@code{foo} is precisely @samp{c}.  (Don't actually write your makefiles
this way!)

A dollar sign followed by a character other than a dollar sign,
open-parenthesis or open-brace treats that single character as the
variable name.  Thus, you could reference the variable @code{x} with
@samp{$x}.  However, this practice is strongly discouraged, except in
the case of the automatic variables (@pxref{Automatic, ,Automatic Variables}).

@node Flavors, Advanced, Reference, Using Variables
@section The Two Flavors of Variables
@cindex flavors of variables
@cindex recursive variable expansion
@cindex variables, flavors
@cindex recursively expanded variables
@cindex variables, recursively expanded

There are two ways that a variable in GNU @code{make} can have a value;
we call them the two @dfn{flavors} of variables.  The two flavors are
distinguished in how they are defined and in what they do when expanded.

@cindex =
The first flavor of variable is a @dfn{recursively expanded} variable.
Variables of this sort are defined by lines using @samp{=}
(@pxref{Setting, ,Setting Variables}) or by the @code{define} directive
(@pxref{Defining, ,Defining Variables Verbatim}).  The value you specify
is installed verbatim; if it contains references to other variables,
these references are expanded whenever this variable is substituted (in
the course of expanding some other string).  When this happens, it is
called @dfn{recursive expansion}.@refill

For example,

@example
foo = $(bar)
bar = $(ugh)
ugh = Huh?

all:;echo $(foo)
@end example

@noindent
will echo @samp{Huh?}: @samp{$(foo)} expands to @samp{$(bar)} which
expands to @samp{$(ugh)} which finally expands to @samp{Huh?}.@refill

This flavor of variable is the only sort supported by other versions of
@code{make}.  It has its advantages and its disadvantages.  An advantage
(most would say) is that:

@example
CFLAGS = $(include_dirs) -O
include_dirs = -Ifoo -Ibar
@end example

@noindent
will do what was intended: when @samp{CFLAGS} is expanded in a command,
it will expand to @samp{-Ifoo -Ibar -O}.  A major disadvantage is that you
cannot append something on the end of a variable, as in

@example
CFLAGS = $(CFLAGS) -O
@end example

@noindent
because it will cause an infinite loop in the variable expansion.
(Actually @code{make} detects the infinite loop and reports an error.)
@cindex loops in variable expansion
@cindex variables, loops in expansion

Another disadvantage is that any functions
(@pxref{Functions, ,Functions for Transforming Text})
referenced in the definition will be executed every time the variable is
expanded.  This makes @code{make} run slower; worse, it causes the
@code{wildcard} and @code{shell} functions to give unpredictable results
because you cannot easily control when they are called, or even how many
times.

To avoid all the problems and inconveniences of recursively expanded
variables, there is another flavor: simply expanded variables.

@cindex simply expanded variables
@cindex variables, simply expanded
@cindex :=
@dfn{Simply expanded variables} are defined by lines using @samp{:=}
(@pxref{Setting, ,Setting Variables}).
The value of a simply expanded variable is scanned
once and for all, expanding any references to other variables and
functions, when the variable is defined.  The actual value of the simply
expanded variable is the result of expanding the text that you write.
It does not contain any references to other variables; it contains their
values @emph{as of the time this variable was defined}.  Therefore,

@example
x := foo
y := $(x) bar
x := later
@end example

@noindent
is equivalent to

@example
y := foo bar
x := later
@end example

When a simply expanded variable is referenced, its value is substituted
verbatim.

Here is a somewhat more complicated example, illustrating the use of
@samp{:=} in conjunction with the @code{shell} function.
(@xref{Shell Function, , The @code{shell} Function}.)  This example
also shows use of the variable @code{MAKELEVEL}, which is changed
when it is passed down from level to level.
(@xref{Variables/Recursion, , Communicating Variables to a
Sub-@code{make}}, for information about @code{MAKELEVEL}.)

@vindex MAKELEVEL
@vindex MAKE
@example
@group
ifeq (0,$@{MAKELEVEL@})
cur-dir   := $(shell pwd)
whoami    := $(shell whoami)
host-type := $(shell arch)
MAKE := $@{MAKE@} host-type=$@{host-type@} whoami=$@{whoami@}
endif
@end group
@end example

@noindent
An advantage of this use of @samp{:=} is that a typical
`descend into a directory' command then looks like this:

@example
@group
$@{subdirs@}:
      $@{MAKE@} cur-dir=$@{cur-dir@}/$@@ -C $@@ all
@end group
@end example

Simply expanded variables generally make complicated makefile programming
more predictable because they work like variables in most programming
languages.  They allow you to redefine a variable using its own value (or
its value processed in some way by one of the expansion functions) and to
use the expansion functions much more efficiently
(@pxref{Functions, ,Functions for Transforming Text}).

@cindex spaces, in variable values
@cindex whitespace, in variable values
@cindex variables, spaces in values
You can also use them to introduce controlled leading whitespace into
variable values.  Leading whitespace characters are discarded from your
input before substitution of variable references and function calls;
this means you can include leading spaces in a variable value by
protecting them with variable references, like this:

@example
nullstring :=
space := $(nullstring) # end of the line
@end example

@noindent
Here the value of the variable @code{space} is precisely one space.  The
comment @w{@samp{# end of the line}} is included here just for clarity.
Since trailing space characters are @emph{not} stripped from variable
values, just a space at the end of the line would have the same effect
(but be rather hard to read).  If you put whitespace at the end of a
variable value, it is a good idea to put a comment like that at the end
of the line to make your intent clear.  Conversely, if you do @emph{not}
want any whitespace characters at the end of your variable value, you
must remember not to put a random comment on the end of the line after
some whitespace, such as this:

@example
dir := /foo/bar    # directory to put the frobs in
@end example

@noindent
Here the value of the variable @code{dir} is @w{@samp{/foo/bar    }}
(with four trailing spaces), which was probably not the intention.
(Imagine something like @w{@samp{$(dir)/file}} with this definition!)

@cindex conditional variable assignment
@cindex variables, conditional assignment
@cindex ?=
There is another assignment operator for variables, @samp{?=}.  This
is called a conditional variable assignment operator, because it only
has an effect if the variable is not yet defined.  This statement:

@example
FOO ?= bar
@end example

@noindent
is exactly equivalent to this
(@pxref{Origin Function, ,The @code{origin} Function}):

@example
ifeq ($(origin FOO), undefined)
  FOO = bar
endif
@end example

Note that a variable set to an empty value is still defined, so
@samp{?=} will not set that variable.

@node Advanced, Values, Flavors, Using Variables
@section Advanced Features for Reference to Variables
@cindex reference to variables

This section describes some advanced features you can use to reference
variables in more flexible ways.

@menu
* Substitution Refs::           Referencing a variable with
                                  substitutions on the value.
* Computed Names::              Computing the name of the variable to refer to.
@end menu

@node Substitution Refs, Computed Names,  , Advanced
@subsection Substitution References
@cindex modified variable reference
@cindex substitution variable reference
@cindex variables, modified reference
@cindex variables, substitution reference

@cindex variables, substituting suffix in
@cindex suffix, substituting in variables
A @dfn{substitution reference} substitutes the value of a variable with
alterations that you specify.  It has the form
@samp{$(@var{var}:@var{a}=@var{b})} (or
@samp{$@{@var{var}:@var{a}=@var{b}@}}) and its meaning is to take the value
of the variable @var{var}, replace every @var{a} at the end of a word with
@var{b} in that value, and substitute the resulting string.

When we say ``at the end of a word'', we mean that @var{a} must appear
either followed by whitespace or at the end of the value in order to be
replaced; other occurrences of @var{a} in the value are unaltered.  For
example:@refill

@example
foo := a.o b.o c.o
bar := $(foo:.o=.c)
@end example

@noindent
sets @samp{bar} to @samp{a.c b.c c.c}.  @xref{Setting, ,Setting Variables}.

A substitution reference is actually an abbreviation for use of the
@code{patsubst} expansion function (@pxref{Text Functions, ,Functions for String Substitution and Analysis}).  We provide
substitution references as well as @code{patsubst} for compatibility with
other implementations of @code{make}.

@findex patsubst
Another type of substitution reference lets you use the full power of
the @code{patsubst} function.  It has the same form
@samp{$(@var{var}:@var{a}=@var{b})} described above, except that now
@var{a} must contain a single @samp{%} character.  This case is
equivalent to @samp{$(patsubst @var{a},@var{b},$(@var{var}))}.
@xref{Text Functions, ,Functions for String Substitution and Analysis},
for a description of the @code{patsubst} function.@refill

@example
@group
@exdent For example:

foo := a.o b.o c.o
bar := $(foo:%.o=%.c)
@end group
@end example

@noindent
sets @samp{bar} to @samp{a.c b.c c.c}.

@node Computed Names,  , Substitution Refs, Advanced
@subsection Computed Variable Names
@cindex nested variable reference
@cindex computed variable name
@cindex variables, computed names
@cindex variables, nested references
@cindex variables, @samp{$} in name
@cindex @code{$}, in variable name
@cindex dollar sign (@code{$}), in variable name

Computed variable names are a complicated concept needed only for
sophisticated makefile programming.  For most purposes you need not
consider them, except to know that making a variable with a dollar sign
in its name might have strange results.  However, if you are the type
that wants to understand everything, or you are actually interested in
what they do, read on.

Variables may be referenced inside the name of a variable.  This is
called a @dfn{computed variable name} or a @dfn{nested variable
reference}.  For example,

@example
x = y
y = z
a := $($(x))
@end example

@noindent
defines @code{a} as @samp{z}: the @samp{$(x)} inside @samp{$($(x))} expands
to @samp{y}, so @samp{$($(x))} expands to @samp{$(y)} which in turn expands
to @samp{z}.  Here the name of the variable to reference is not stated
explicitly; it is computed by expansion of @samp{$(x)}.  The reference
@samp{$(x)} here is nested within the outer variable reference.

The previous example shows two levels of nesting, but any number of levels
is possible.  For example, here are three levels:

@example
x = y
y = z
z = u
a := $($($(x)))
@end example

@noindent
Here the innermost @samp{$(x)} expands to @samp{y}, so @samp{$($(x))}
expands to @samp{$(y)} which in turn expands to @samp{z}; now we have
@samp{$(z)}, which becomes @samp{u}.

References to recursively-expanded variables within a variable name are
reexpanded in the usual fashion.  For example:

@example
x = $(y)
y = z
z = Hello
a := $($(x))
@end example

@noindent
defines @code{a} as @samp{Hello}: @samp{$($(x))} becomes @samp{$($(y))}
which becomes @samp{$(z)} which becomes @samp{Hello}.

Nested variable references can also contain modified references and
function invocations (@pxref{Functions, ,Functions for Transforming Text}),
just like any other reference.
For example, using the @code{subst} function
(@pxref{Text Functions, ,Functions for String Substitution and Analysis}):

@example
@group
x = variable1
variable2 := Hello
y = $(subst 1,2,$(x))
z = y
a := $($($(z)))
@end group
@end example

@noindent
eventually defines @code{a} as @samp{Hello}.  It is doubtful that anyone
would ever want to write a nested reference as convoluted as this one, but
it works: @samp{$($($(z)))} expands to @samp{$($(y))} which becomes
@samp{$($(subst 1,2,$(x)))}.  This gets the value @samp{variable1} from
@code{x} and changes it by substitution to @samp{variable2}, so that the
entire string becomes @samp{$(variable2)}, a simple variable reference
whose value is @samp{Hello}.@refill

A computed variable name need not consist entirely of a single variable
reference.  It can contain several variable references, as well as some
invariant text.  For example,

@example
@group
a_dirs := dira dirb
1_dirs := dir1 dir2
@end group

@group
a_files := filea fileb
1_files := file1 file2
@end group

@group
ifeq "$(use_a)" "yes"
a1 := a
else
a1 := 1
endif
@end group

@group
ifeq "$(use_dirs)" "yes"
df := dirs
else
df := files
endif

dirs := $($(a1)_$(df))
@end group
@end example

@noindent
will give @code{dirs} the same value as @code{a_dirs}, @code{1_dirs},
@code{a_files} or @code{1_files} depending on the settings of @code{use_a}
and @code{use_dirs}.@refill

Computed variable names can also be used in substitution references:

@example
@group
a_objects := a.o b.o c.o
1_objects := 1.o 2.o 3.o

sources := $($(a1)_objects:.o=.c)
@end group
@end example

@noindent
defines @code{sources} as either @samp{a.c b.c c.c} or @samp{1.c 2.c 3.c},
depending on the value of @code{a1}.

The only restriction on this sort of use of nested variable references
is that they cannot specify part of the name of a function to be called.
This is because the test for a recognized function name is done before
the expansion of nested references.  For example,

@example
@group
ifdef do_sort
func := sort
else
func := strip
endif
@end group

@group
bar := a d b g q c
@end group

@group
foo := $($(func) $(bar))
@end group
@end example

@noindent
attempts to give @samp{foo} the value of the variable @samp{sort a d b g
q c} or @samp{strip a d b g q c}, rather than giving @samp{a d b g q c}
as the argument to either the @code{sort} or the @code{strip} function.
This restriction could be removed in the future if that change is shown
to be a good idea.

You can also use computed variable names in the left-hand side of a
variable assignment, or in a @code{define} directive, as in:

@example
dir = foo
$(dir)_sources := $(wildcard $(dir)/*.c)
define $(dir)_print
lpr $($(dir)_sources)
endef
@end example

@noindent
This example defines the variables @samp{dir}, @samp{foo_sources}, and
@samp{foo_print}.

Note that @dfn{nested variable references} are quite different from
@dfn{recursively expanded variables}
(@pxref{Flavors, ,The Two Flavors of Variables}), though both are
used together in complex ways when doing makefile programming.@refill

@node Values, Setting, Advanced, Using Variables
@section How Variables Get Their Values
@cindex variables, how they get their values
@cindex value, how a variable gets it

Variables can get values in several different ways:

@itemize @bullet
@item
You can specify an overriding value when you run @code{make}.
@xref{Overriding, ,Overriding Variables}.

@item
You can specify a value in the makefile, either
with an assignment (@pxref{Setting, ,Setting Variables}) or with a
verbatim definition (@pxref{Defining, ,Defining Variables Verbatim}).@refill

@item
Variables in the environment become @code{make} variables.
@xref{Environment, ,Variables from the Environment}.

@item
Several @dfn{automatic} variables are given new values for each rule.
Each of these has a single conventional use.
@xref{Automatic, ,Automatic Variables}.

@item
Several variables have constant initial values.
@xref{Implicit Variables, ,Variables Used by Implicit Rules}.
@end itemize

@node Setting, Appending, Values, Using Variables
@section Setting Variables
@cindex setting variables
@cindex variables, setting
@cindex =
@cindex :=
@cindex ?=

To set a variable from the makefile, write a line starting with the
variable name followed by @samp{=} or @samp{:=}.  Whatever follows the
@samp{=} or @samp{:=} on the line becomes the value.  For example,

@example
objects = main.o foo.o bar.o utils.o
@end example

@noindent
defines a variable named @code{objects}.  Whitespace around the variable
name and immediately after the @samp{=} is ignored.

Variables defined with @samp{=} are @dfn{recursively expanded} variables.
Variables defined with @samp{:=} are @dfn{simply expanded} variables; these
definitions can contain variable references which will be expanded before
the definition is made.  @xref{Flavors, ,The Two Flavors of Variables}.

The variable name may contain function and variable references, which
are expanded when the line is read to find the actual variable name to use.

There is no limit on the length of the value of a variable except the
amount of swapping space on the computer.  When a variable definition is
long, it is a good idea to break it into several lines by inserting
backslash-newline at convenient places in the definition.  This will not
affect the functioning of @code{make}, but it will make the makefile easier
to read.

Most variable names are considered to have the empty string as a value if
you have never set them.  Several variables have built-in initial values
that are not empty, but you can set them in the usual ways
(@pxref{Implicit Variables, ,Variables Used by Implicit Rules}).
Several special variables are set
automatically to a new value for each rule; these are called the
@dfn{automatic} variables (@pxref{Automatic, ,Automatic Variables}).

If you'd like a variable to be set to a value only if it's not already
set, then you can use the shorthand operator @samp{?=} instead of
@samp{=}.  These two settings of the variable @samp{FOO} are identical
(@pxref{Origin Function, ,The @code{origin} Function}):

@example
FOO ?= bar
@end example

@noindent
and

@example
ifeq ($(origin FOO), undefined)
FOO = bar
endif
@end example

@node Appending, Override Directive, Setting, Using Variables
@section Appending More Text to Variables
@cindex +=
@cindex appending to variables
@cindex variables, appending to

Often it is useful to add more text to the value of a variable already defined.
You do this with a line containing @samp{+=}, like this:

@example
objects += another.o
@end example

@noindent
This takes the value of the variable @code{objects}, and adds the text
@samp{another.o} to it (preceded by a single space).  Thus:

@example
objects = main.o foo.o bar.o utils.o
objects += another.o
@end example

@noindent
sets @code{objects} to @samp{main.o foo.o bar.o utils.o another.o}.

Using @samp{+=} is similar to:

@example
objects = main.o foo.o bar.o utils.o
objects := $(objects) another.o
@end example

@noindent
but differs in ways that become important when you use more complex values.

When the variable in question has not been defined before, @samp{+=}
acts just like normal @samp{=}: it defines a recursively-expanded
variable.  However, when there @emph{is} a previous definition, exactly
what @samp{+=} does depends on what flavor of variable you defined
originally.  @xref{Flavors, ,The Two Flavors of Variables}, for an
explanation of the two flavors of variables.

When you add to a variable's value with @samp{+=}, @code{make} acts
essentially as if you had included the extra text in the initial
definition of the variable.  If you defined it first with @samp{:=},
making it a simply-expanded variable, @samp{+=} adds to that
simply-expanded definition, and expands the new text before appending it
to the old value just as @samp{:=} does
(@pxref{Setting, ,Setting Variables}, for a full explanation of @samp{:=}).
In fact,

@example
variable := value
variable += more
@end example

@noindent
is exactly equivalent to:

@noindent
@example
variable := value
variable := $(variable) more
@end example

On the other hand, when you use @samp{+=} with a variable that you defined
first to be recursively-expanded using plain @samp{=}, @code{make} does
something a bit different.  Recall that when you define a
recursively-expanded variable, @code{make} does not expand the value you set
for variable and function references immediately.  Instead it stores the text
verbatim, and saves these variable and function references to be expanded
later, when you refer to the new variable (@pxref{Flavors, ,The Two Flavors
of Variables}).  When you use @samp{+=} on a recursively-expanded variable,
it is this unexpanded text to which @code{make} appends the new text you
specify.

@example
@group
variable = value
variable += more
@end group
@end example

@noindent
is roughly equivalent to:

@example
@group
temp = value
variable = $(temp) more
@end group
@end example

@noindent
except that of course it never defines a variable called @code{temp}.
The importance of this comes when the variable's old value contains
variable references.  Take this common example:

@example
CFLAGS = $(includes) -O
@dots{}
CFLAGS += -pg # enable profiling
@end example

@noindent
The first line defines the @code{CFLAGS} variable with a reference to another
variable, @code{includes}.  (@code{CFLAGS} is used by the rules for C
compilation; @pxref{Catalogue of Rules, ,Catalogue of Implicit Rules}.)
Using @samp{=} for the definition makes @code{CFLAGS} a recursively-expanded
variable, meaning @w{@samp{$(includes) -O}} is @emph{not} expanded when
@code{make} processes the definition of @code{CFLAGS}.  Thus, @code{includes}
need not be defined yet for its value to take effect.  It only has to be
defined before any reference to @code{CFLAGS}.  If we tried to append to the
value of @code{CFLAGS} without using @samp{+=}, we might do it like this:

@example
CFLAGS := $(CFLAGS) -pg # enable profiling
@end example

@noindent
This is pretty close, but not quite what we want.  Using @samp{:=}
redefines @code{CFLAGS} as a simply-expanded variable; this means
@code{make} expands the text @w{@samp{$(CFLAGS) -pg}} before setting the
variable.  If @code{includes} is not yet defined, we get @w{@samp{ -O
-pg}}, and a later definition of @code{includes} will have no effect.
Conversely, by using @samp{+=} we set @code{CFLAGS} to the
@emph{unexpanded} value @w{@samp{$(includes) -O -pg}}.  Thus we preserve
the reference to @code{includes}, so if that variable gets defined at
any later point, a reference like @samp{$(CFLAGS)} still uses its
value.

@node Override Directive, Defining, Appending, Using Variables
@section The @code{override} Directive
@findex override
@cindex overriding with @code{override}
@cindex variables, overriding

If a variable has been set with a command argument
(@pxref{Overriding, ,Overriding Variables}),
then ordinary assignments in the makefile are ignored.  If you want to set
the variable in the makefile even though it was set with a command
argument, you can use an @code{override} directive, which is a line that
looks like this:@refill

@example
override @var{variable} = @var{value}
@end example

@noindent
or

@example
override @var{variable} := @var{value}
@end example

To append more text to a variable defined on the command line, use:

@example
override @var{variable} += @var{more text}
@end example

@noindent
@xref{Appending, ,Appending More Text to Variables}.

The @code{override} directive was not invented for escalation in the war
between makefiles and command arguments.  It was invented so you can alter
and add to values that the user specifies with command arguments.

For example, suppose you always want the @samp{-g} switch when you run the
C compiler, but you would like to allow the user to specify the other
switches with a command argument just as usual.  You could use this
@code{override} directive:

@example
override CFLAGS += -g
@end example

You can also use @code{override} directives with @code{define} directives.
This is done as you might expect:

@example
override define foo
bar
endef
@end example

@noindent
@iftex
See the next section for information about @code{define}.
@end iftex
@ifinfo
@xref{Defining, ,Defining Variables Verbatim}.
@end ifinfo

@node Defining, Environment, Override Directive, Using Variables
@section Defining Variables Verbatim
@findex define
@findex endef
@cindex verbatim variable definition
@cindex defining variables verbatim
@cindex variables, defining verbatim

Another way to set the value of a variable is to use the @code{define}
directive.  This directive has an unusual syntax which allows newline
characters to be included in the value, which is convenient for defining
canned sequences of commands
(@pxref{Sequences, ,Defining Canned Command Sequences}).

The @code{define} directive is followed on the same line by the name of the
variable and nothing more.  The value to give the variable appears on the
following lines.  The end of the value is marked by a line containing just
the word @code{endef}.  Aside from this difference in syntax, @code{define}
works just like @samp{=}: it creates a recursively-expanded variable
(@pxref{Flavors, ,The Two Flavors of Variables}).
The variable name may contain function and variable references, which
are expanded when the directive is read to find the actual variable name
to use.

@example
define two-lines
echo foo
echo $(bar)
endef
@end example

The value in an ordinary assignment cannot contain a newline; but the
newlines that separate the lines of the value in a @code{define} become
part of the variable's value (except for the final newline which precedes
the @code{endef} and is not considered part of the value).@refill

@need 800
The previous example is functionally equivalent to this:

@example
two-lines = echo foo; echo $(bar)
@end example

@noindent
since two commands separated by semicolon behave much like two separate
shell commands.  However, note that using two separate lines means
@code{make} will invoke the shell twice, running an independent subshell
for each line.  @xref{Execution, ,Command Execution}.

If you want variable definitions made with @code{define} to take
precedence over command-line variable definitions, you can use the
@code{override} directive together with @code{define}:

@example
override define two-lines
foo
$(bar)
endef
@end example

@noindent
@xref{Override Directive, ,The @code{override} Directive}.

@node Environment, Target-specific, Defining, Using Variables
@section Variables from the Environment

@cindex variables, environment
@cindex environment
Variables in @code{make} can come from the environment in which
@code{make} is run.  Every environment variable that @code{make} sees when
it starts up is transformed into a @code{make} variable with the same name
and value.  But an explicit assignment in the makefile, or with a command
argument, overrides the environment.  (If the @samp{-e} flag is specified,
then values from the environment override assignments in the makefile.
@xref{Options Summary, ,Summary of Options}.
But this is not recommended practice.)

Thus, by setting the variable @code{CFLAGS} in your environment, you can
cause all C compilations in most makefiles to use the compiler switches you
prefer.  This is safe for variables with standard or conventional meanings
because you know that no makefile will use them for other things.  (But
this is not totally reliable; some makefiles set @code{CFLAGS} explicitly
and therefore are not affected by the value in the environment.)

When @code{make} is invoked recursively, variables defined in the
outer invocation can be passed to inner invocations through the
environment (@pxref{Recursion, ,Recursive Use of @code{make}}).  By
default, only variables that came from the environment or the command
line are passed to recursive invocations.  You can use the
@code{export} directive to pass other variables.
@xref{Variables/Recursion, , Communicating Variables to a
Sub-@code{make}}, for full details.

Other use of variables from the environment is not recommended.  It is not
wise for makefiles to depend for their functioning on environment variables
set up outside their control, since this would cause different users to get
different results from the same makefile.  This is against the whole
purpose of most makefiles.

Such problems would be especially likely with the variable @code{SHELL},
which is normally present in the environment to specify the user's choice
of interactive shell.  It would be very undesirable for this choice to
affect @code{make}.  So @code{make} ignores the environment value of
@code{SHELL} (except on MS-DOS and MS-Windows, where @code{SHELL} is
usually not set.  @xref{Execution, ,Special handling of SHELL on
MS-DOS}.)@refill

@node Target-specific, Pattern-specific, Environment, Using Variables
@section Target-specific Variable Values
@cindex target-specific variables
@cindex variables, target-specific

Variable values in @code{make} are usually global; that is, they are the
same regardless of where they are evaluated (unless they're reset, of
course).  One exception to that is automatic variables
(@pxref{Automatic, ,Automatic Variables}).

The other exception is @dfn{target-specific variable values}.  This
feature allows you to define different values for the same variable,
based on the target that @code{make} is currently building.  As with
automatic variables, these values are only available within the context
of a target's command script (and in other target-specific assignments).

Set a target-specific variable value like this:

@example
@var{target} @dots{} : @var{variable-assignment}
@end example

@noindent
or like this:

@example
@var{target} @dots{} : override @var{variable-assignment}
@end example

Multiple @var{target} values create a target-specific variable value for
each member of the target list individually.

The @var{variable-assignment} can be any valid form of assignment;
recursive (@samp{=}), static (@samp{:=}), appending (@samp{+=}), or
conditional (@samp{?=}).  All variables that appear within the
@var{variable-assignment} are evaluated within the context of the
target: thus, any previously-defined target-specific variable values
will be in effect.  Note that this variable is actually distinct from
any ``global'' value: the two variables do not have to have the same
flavor (recursive vs. static).

Target-specific variables have the same priority as any other makefile
variable.  Variables provided on the command-line (and in the
environment if the @samp{-e} option is in force) will take precedence.
Specifying the @code{override} directive will allow the target-specific
variable value to be preferred.

There is one more special feature of target-specific variables: when you
define a target-specific variable, that variable value is also in effect
for all prerequisites of this target (unless those prerequisites override
it with their own target-specific variable value).  So, for example, a
statement like this:

@example
prog : CFLAGS = -g
prog : prog.o foo.o bar.o
@end example

@noindent
will set @code{CFLAGS} to @samp{-g} in the command script for
@file{prog}, but it will also set @code{CFLAGS} to @samp{-g} in the
command scripts that create @file{prog.o}, @file{foo.o}, and
@file{bar.o}, and any command scripts which create their prerequisites.

@node Pattern-specific,  , Target-specific, Using Variables
@section Pattern-specific Variable Values
@cindex pattern-specific variables
@cindex variables, pattern-specific

In addition to target-specific variable values (@pxref{Target-specific,
,Target-specific Variable Values}), GNU @code{make} supports
pattern-specific variable values.  In this form, a variable is defined
for any target that matches the pattern specified.  Variables defined in
this way are searched after any target-specific variables defined
explicitly for that target, and before target-specific variables defined
for the parent target.

Set a pattern-specific variable value like this:

@example
@var{pattern} @dots{} : @var{variable-assignment}
@end example

@noindent
or like this:

@example
@var{pattern} @dots{} : override @var{variable-assignment}
@end example

@noindent
where @var{pattern} is a %-pattern.  As with target-specific variable
values, multiple @var{pattern} values create a pattern-specific variable
value for each pattern individually.  The @var{variable-assignment} can
be any valid form of assignment.  Any command-line variable setting will
take precedence, unless @code{override} is specified.

For example:

@example
%.o : CFLAGS = -O
@end example

@noindent
will assign @code{CFLAGS} the value of @samp{-O} for all targets
matching the pattern @code{%.o}.

@node Conditionals, Functions, Using Variables, Top
@chapter Conditional Parts of Makefiles

@cindex conditionals
A @dfn{conditional} causes part of a makefile to be obeyed or ignored
depending on the values of variables.  Conditionals can compare the
value of one variable to another, or the value of a variable to
a constant string.  Conditionals control what @code{make} actually
``sees'' in the makefile, so they @emph{cannot} be used to control shell
commands at the time of execution.@refill

@menu
* Conditional Example::         Example of a conditional
* Conditional Syntax::          The syntax of conditionals.
* Testing Flags::               Conditionals that test flags.
@end menu

@node Conditional Example, Conditional Syntax,  , Conditionals
@section Example of a Conditional

The following example of a conditional tells @code{make} to use one set
of libraries if the @code{CC} variable is @samp{gcc}, and a different
set of libraries otherwise.  It works by controlling which of two
command lines will be used as the command for a rule.  The result is
that @samp{CC=gcc} as an argument to @code{make} changes not only which
compiler is used but also which libraries are linked.

@example
libs_for_gcc = -lgnu
normal_libs =

foo: $(objects)
ifeq ($(CC),gcc)
        $(CC) -o foo $(objects) $(libs_for_gcc)
else
        $(CC) -o foo $(objects) $(normal_libs)
endif
@end example

This conditional uses three directives: one @code{ifeq}, one @code{else}
and one @code{endif}.

The @code{ifeq} directive begins the conditional, and specifies the
condition.  It contains two arguments, separated by a comma and surrounded
by parentheses.  Variable substitution is performed on both arguments and
then they are compared.  The lines of the makefile following the
@code{ifeq} are obeyed if the two arguments match; otherwise they are
ignored.

The @code{else} directive causes the following lines to be obeyed if the
previous conditional failed.  In the example above, this means that the
second alternative linking command is used whenever the first alternative
is not used.  It is optional to have an @code{else} in a conditional.

The @code{endif} directive ends the conditional.  Every conditional must
end with an @code{endif}.  Unconditional makefile text follows.

As this example illustrates, conditionals work at the textual level:
the lines of the conditional are treated as part of the makefile, or
ignored, according to the condition.  This is why the larger syntactic
units of the makefile, such as rules, may cross the beginning or the
end of the conditional.

When the variable @code{CC} has the value @samp{gcc}, the above example has
this effect:

@example
foo: $(objects)
        $(CC) -o foo $(objects) $(libs_for_gcc)
@end example

@noindent
When the variable @code{CC} has any other value, the effect is this:

@example
foo: $(objects)
        $(CC) -o foo $(objects) $(normal_libs)
@end example

Equivalent results can be obtained in another way by conditionalizing a
variable assignment and then using the variable unconditionally:

@example
libs_for_gcc = -lgnu
normal_libs =

ifeq ($(CC),gcc)
  libs=$(libs_for_gcc)
else
  libs=$(normal_libs)
endif

foo: $(objects)
        $(CC) -o foo $(objects) $(libs)
@end example

@node Conditional Syntax, Testing Flags, Conditional Example, Conditionals
@section Syntax of Conditionals
@findex ifdef
@findex ifeq
@findex ifndef
@findex ifneq
@findex else
@findex endif

The syntax of a simple conditional with no @code{else} is as follows:

@example
@var{conditional-directive}
@var{text-if-true}
endif
@end example

@noindent
The @var{text-if-true} may be any lines of text, to be considered as part
of the makefile if the condition is true.  If the condition is false, no
text is used instead.

The syntax of a complex conditional is as follows:

@example
@var{conditional-directive}
@var{text-if-true}
else
@var{text-if-false}
endif
@end example

@noindent
If the condition is true, @var{text-if-true} is used; otherwise,
@var{text-if-false} is used instead.  The @var{text-if-false} can be any
number of lines of text.

The syntax of the @var{conditional-directive} is the same whether the
conditional is simple or complex.  There are four different directives that
test different conditions.  Here is a table of them:

@table @code
@item ifeq (@var{arg1}, @var{arg2})
@itemx ifeq '@var{arg1}' '@var{arg2}'
@itemx ifeq "@var{arg1}" "@var{arg2}"
@itemx ifeq "@var{arg1}" '@var{arg2}'
@itemx ifeq '@var{arg1}' "@var{arg2}"
Expand all variable references in @var{arg1} and @var{arg2} and
compare them.  If they are identical, the @var{text-if-true} is
effective; otherwise, the @var{text-if-false}, if any, is effective.

Often you want to test if a variable has a non-empty value.  When the
value results from complex expansions of variables and functions,
expansions you would consider empty may actually contain whitespace
characters and thus are not seen as empty.  However, you can use the
@code{strip} function (@pxref{Text Functions}) to avoid interpreting
whitespace as a non-empty value.  For example:

@example
@group
ifeq ($(strip $(foo)),)
@var{text-if-empty}
endif
@end group
@end example

@noindent
will evaluate @var{text-if-empty} even if the expansion of
@code{$(foo)} contains whitespace characters.

@item ifneq (@var{arg1}, @var{arg2})
@itemx ifneq '@var{arg1}' '@var{arg2}'
@itemx ifneq "@var{arg1}" "@var{arg2}"
@itemx ifneq "@var{arg1}" '@var{arg2}'
@itemx ifneq '@var{arg1}' "@var{arg2}"
Expand all variable references in @var{arg1} and @var{arg2} and
compare them.  If they are different, the @var{text-if-true} is
effective; otherwise, the @var{text-if-false}, if any, is effective.

@item ifdef @var{variable-name}
If the variable @var{variable-name} has a non-empty value, the
@var{text-if-true} is effective; otherwise, the @var{text-if-false},
if any, is effective.  Variables that have never been defined have an
empty value.

Note that @code{ifdef} only tests whether a variable has a value.  It
does not expand the variable to see if that value is nonempty.
Consequently, tests using @code{ifdef} return true for all definitions
except those like @code{foo =}.  To test for an empty value, use
@w{@code{ifeq ($(foo),)}}.  For example,

@example
bar =
foo = $(bar)
ifdef foo
frobozz = yes
else
frobozz = no
endif
@end example

@noindent
sets @samp{frobozz} to @samp{yes}, while:

@example
foo =
ifdef foo
frobozz = yes
else
frobozz = no
endif
@end example

@noindent
sets @samp{frobozz} to @samp{no}.

@item ifndef @var{variable-name}
If the variable @var{variable-name} has an empty value, the
@var{text-if-true} is effective; otherwise, the @var{text-if-false},
if any, is effective.
@end table

Extra spaces are allowed and ignored at the beginning of the conditional
directive line, but a tab is not allowed.  (If the line begins with a tab,
it will be considered a command for a rule.)  Aside from this, extra spaces
or tabs may be inserted with no effect anywhere except within the directive
name or within an argument.  A comment starting with @samp{#} may appear at
the end of the line.

The other two directives that play a part in a conditional are @code{else}
and @code{endif}.  Each of these directives is written as one word, with no
arguments.  Extra spaces are allowed and ignored at the beginning of the
line, and spaces or tabs at the end.  A comment starting with @samp{#} may
appear at the end of the line.

Conditionals affect which lines of the makefile @code{make} uses.  If
the condition is true, @code{make} reads the lines of the
@var{text-if-true} as part of the makefile; if the condition is false,
@code{make} ignores those lines completely.  It follows that syntactic
units of the makefile, such as rules, may safely be split across the
beginning or the end of the conditional.@refill

@code{make} evaluates conditionals when it reads a makefile.
Consequently, you cannot use automatic variables in the tests of
conditionals because they are not defined until commands are run
(@pxref{Automatic, , Automatic Variables}).

To prevent intolerable confusion, it is not permitted to start a
conditional in one makefile and end it in another.  However, you may
write an @code{include} directive within a conditional, provided you do
not attempt to terminate the conditional inside the included file.

@node Testing Flags,  , Conditional Syntax, Conditionals
@section Conditionals that Test Flags

You can write a conditional that tests @code{make} command flags such as
@samp{-t} by using the variable @code{MAKEFLAGS} together with the
@code{findstring} function
(@pxref{Text Functions, , Functions for String Substitution and Analysis}).
This is useful when @code{touch} is not enough to make a file appear up
to date.

The @code{findstring} function determines whether one string appears as a
substring of another.  If you want to test for the @samp{-t} flag,
use @samp{t} as the first string and the value of @code{MAKEFLAGS} as
the other.

For example, here is how to arrange to use @samp{ranlib -t} to finish
marking an archive file up to date:

@example
archive.a: @dots{}
ifneq (,$(findstring t,$(MAKEFLAGS)))
        +touch archive.a
        +ranlib -t archive.a
else
        ranlib archive.a
endif
@end example

@noindent
The @samp{+} prefix marks those command lines as ``recursive'' so
that they will be executed despite use of the @samp{-t} flag.
@xref{Recursion, ,Recursive Use of @code{make}}.

@node Functions, Running, Conditionals, Top
@chapter Functions for Transforming Text
@cindex functions

@dfn{Functions} allow you to do text processing in the makefile to compute
the files to operate on or the commands to use.  You use a function in a
@dfn{function call}, where you give the name of the function and some text
(the @dfn{arguments}) for the function to operate on.  The result of the
function's processing is substituted into the makefile at the point of the
call, just as a variable might be substituted.

@menu
* Syntax of Functions::         How to write a function call.
* Text Functions::              General-purpose text manipulation functions.
* File Name Functions::         Functions for manipulating file names.
* Foreach Function::            Repeat some text with controlled variation.
* If Function::                 Conditionally expand a value.
* Call Function::               Expand a user-defined function.
* Origin Function::             Find where a variable got its value.
* Shell Function::              Substitute the output of a shell command.
* Make Control Functions::      Functions that control how make runs.
@end menu

@node Syntax of Functions, Text Functions,  , Functions
@section Function Call Syntax
@cindex @code{$}, in function call
@cindex dollar sign (@code{$}), in function call
@cindex arguments of functions
@cindex functions, syntax of

A function call resembles a variable reference.  It looks like this:

@example
$(@var{function} @var{arguments})
@end example

@noindent
or like this:

@example
$@{@var{function} @var{arguments}@}
@end example

Here @var{function} is a function name; one of a short list of names
that are part of @code{make}.  You can also essentially create your own
functions by using the @code{call} builtin function.

The @var{arguments} are the arguments of the function.  They are
separated from the function name by one or more spaces or tabs, and if
there is more than one argument, then they are separated by commas.
Such whitespace and commas are not part of an argument's value.  The
delimiters which you use to surround the function call, whether
parentheses or braces, can appear in an argument only in matching pairs;
the other kind of delimiters may appear singly.  If the arguments
themselves contain other function calls or variable references, it is
wisest to use the same kind of delimiters for all the references; write
@w{@samp{$(subst a,b,$(x))}}, not @w{@samp{$(subst a,b,$@{x@})}}.  This
is because it is clearer, and because only one type of delimiter is
matched to find the end of the reference.

The text written for each argument is processed by substitution of
variables and function calls to produce the argument value, which
is the text on which the function acts.  The substitution is done in the
order in which the arguments appear.

Commas and unmatched parentheses or braces cannot appear in the text of an
argument as written; leading spaces cannot appear in the text of the first
argument as written.  These characters can be put into the argument value
by variable substitution.  First define variables @code{comma} and
@code{space} whose values are isolated comma and space characters, then
substitute these variables where such characters are wanted, like this:

@example
@group
comma:= ,
empty:=
space:= $(empty) $(empty)
foo:= a b c
bar:= $(subst $(space),$(comma),$(foo))
# @r{bar is now `a,b,c'.}
@end group
@end example

@noindent
Here the @code{subst} function replaces each space with a comma, through
the value of @code{foo}, and substitutes the result.

@node Text Functions, File Name Functions, Syntax of Functions, Functions
@section Functions for String Substitution and Analysis
@cindex functions, for text

Here are some functions that operate on strings:

@table @code
@item $(subst @var{from},@var{to},@var{text})
@findex subst
Performs a textual replacement on the text @var{text}: each occurrence
of @var{from} is replaced by @var{to}.  The result is substituted for
the function call.  For example,

@example
$(subst ee,EE,feet on the street)
@end example

substitutes the string @samp{fEEt on the strEEt}.

@item $(patsubst @var{pattern},@var{replacement},@var{text})
@findex patsubst
Finds whitespace-separated words in @var{text} that match
@var{pattern} and replaces them with @var{replacement}.  Here
@var{pattern} may contain a @samp{%} which acts as a wildcard,
matching any number of any characters within a word.  If
@var{replacement} also contains a @samp{%}, the @samp{%} is replaced
by the text that matched the @samp{%} in @var{pattern}.@refill

@cindex @code{%}, quoting in @code{patsubst}
@cindex @code{%}, quoting with @code{\} (backslash)
@cindex @code{\} (backslash), to quote @code{%}
@cindex backslash (@code{\}), to quote @code{%}
@cindex quoting @code{%}, in @code{patsubst}
@samp{%} characters in @code{patsubst} function invocations can be
quoted with preceding backslashes (@samp{\}).  Backslashes that would
otherwise quote @samp{%} characters can be quoted with more backslashes.
Backslashes that quote @samp{%} characters or other backslashes are
removed from the pattern before it is compared file names or has a stem
substituted into it.  Backslashes that are not in danger of quoting
@samp{%} characters go unmolested.  For example, the pattern
@file{the\%weird\\%pattern\\} has @samp{the%weird\} preceding the
operative @samp{%} character, and @samp{pattern\\} following it.  The
final two backslashes are left alone because they cannot affect any
@samp{%} character.@refill

Whitespace between words is folded into single space characters;
leading and trailing whitespace is discarded.

For example,

@example
$(patsubst %.c,%.o,x.c.c bar.c)
@end example

@noindent
produces the value @samp{x.c.o bar.o}.

Substitution references (@pxref{Substitution Refs, ,Substitution
References}) are a simpler way to get the effect of the @code{patsubst}
function:

@example
$(@var{var}:@var{pattern}=@var{replacement})
@end example

@noindent
is equivalent to

@example
$(patsubst @var{pattern},@var{replacement},$(@var{var}))
@end example

The second shorthand simplifies one of the most common uses of
@code{patsubst}: replacing the suffix at the end of file names.

@example
$(@var{var}:@var{suffix}=@var{replacement})
@end example

@noindent
is equivalent to

@example
$(patsubst %@var{suffix},%@var{replacement},$(@var{var}))
@end example

@noindent
For example, you might have a list of object files:

@example
objects = foo.o bar.o baz.o
@end example

@noindent
To get the list of corresponding source files, you could simply write:

@example
$(objects:.o=.c)
@end example

@noindent
instead of using the general form:

@example
$(patsubst %.o,%.c,$(objects))
@end example

@item $(strip @var{string})
@cindex stripping whitespace
@cindex whitespace, stripping
@cindex spaces, stripping
@findex strip
Removes leading and trailing whitespace from @var{string} and replaces
each internal sequence of one or more whitespace characters with a
single space.  Thus, @samp{$(strip a b  c )} results in @w{@samp{a b c}}.

The function @code{strip} can be very useful when used in conjunction
with conditionals.  When comparing something with the empty string
@samp{} using @code{ifeq} or @code{ifneq}, you usually want a string of
just whitespace to match the empty string (@pxref{Conditionals}).

Thus, the following may fail to have the desired results:

@example
.PHONY: all
ifneq   "$(needs_made)" ""
all: $(needs_made)
else
all:;@@echo 'Nothing to make!'
endif
@end example

@noindent
Replacing the variable reference @w{@samp{$(needs_made)}} with the
function call @w{@samp{$(strip $(needs_made))}} in the @code{ifneq}
directive would make it more robust.@refill

@item $(findstring @var{find},@var{in})
@findex findstring
@cindex searching for strings
@cindex finding strings
@cindex strings, searching for
Searches @var{in} for an occurrence of @var{find}.  If it occurs, the
value is @var{find}; otherwise, the value is empty.  You can use this
function in a conditional to test for the presence of a specific
substring in a given string.  Thus, the two examples,

@example
$(findstring a,a b c)
$(findstring a,b c)
@end example

@noindent
produce the values @samp{a} and @samp{} (the empty string),
respectively.  @xref{Testing Flags}, for a practical application of
@code{findstring}.@refill

@need 750
@findex filter
@cindex filtering words
@cindex words, filtering
@item $(filter @var{pattern}@dots{},@var{text})
Returns all whitespace-separated words in @var{text} that @emph{do} match
any of the @var{pattern} words, removing any words that @emph{do not}
match.  The patterns are written using @samp{%}, just like the patterns
used in the @code{patsubst} function above.@refill

The @code{filter} function can be used to separate out different types
of strings (such as file names) in a variable.  For example:

@example
sources := foo.c bar.c baz.s ugh.h
foo: $(sources)
        cc $(filter %.c %.s,$(sources)) -o foo
@end example

@noindent
says that @file{foo} depends of @file{foo.c}, @file{bar.c},
@file{baz.s} and @file{ugh.h} but only @file{foo.c}, @file{bar.c} and
@file{baz.s} should be specified in the command to the
compiler.@refill

@item $(filter-out @var{pattern}@dots{},@var{text})
@findex filter-out
@cindex filtering out words
@cindex words, filtering out
Returns all whitespace-separated words in @var{text} that @emph{do not}
match any of the @var{pattern} words, removing the words that @emph{do}
match one or more.  This is the exact opposite of the @code{filter}
function.@refill

Removes all whitespace-separated words in @var{text} that @emph{do}
match the @var{pattern} words, returning only the words that @emph{do
not} match.  This is the exact opposite of the @code{filter}
function.@refill

For example, given:

@example
@group
objects=main1.o foo.o main2.o bar.o
mains=main1.o main2.o
@end group
@end example

@noindent
the following generates a list which contains all the object files not
in @samp{mains}:

@example
$(filter-out $(mains),$(objects))
@end example

@need 1500
@findex sort
@cindex sorting words
@item $(sort @var{list})
Sorts the words of @var{list} in lexical order, removing duplicate
words.  The output is a list of words separated by single spaces.
Thus,

@example
$(sort foo bar lose)
@end example

@noindent
returns the value @samp{bar foo lose}.

@cindex removing duplicate words
@cindex duplicate words, removing
@cindex words, removing duplicates
Incidentally, since @code{sort} removes duplicate words, you can use
it for this purpose even if you don't care about the sort order.
@end table

Here is a realistic example of the use of @code{subst} and
@code{patsubst}.  Suppose that a makefile uses the @code{VPATH} variable
to specify a list of directories that @code{make} should search for
prerequisite files
(@pxref{General Search, , @code{VPATH} Search Path for All Prerequisites}).
This example shows how to
tell the C compiler to search for header files in the same list of
directories.@refill

The value of @code{VPATH} is a list of directories separated by colons,
such as @samp{src:../headers}.  First, the @code{subst} function is used to
change the colons to spaces:

@example
$(subst :, ,$(VPATH))
@end example

@noindent
This produces @samp{src ../headers}.  Then @code{patsubst} is used to turn
each directory name into a @samp{-I} flag.  These can be added to the
value of the variable @code{CFLAGS}, which is passed automatically to the C
compiler, like this:

@example
override CFLAGS += $(patsubst %,-I%,$(subst :, ,$(VPATH)))
@end example

@noindent
The effect is to append the text @samp{-Isrc -I../headers} to the
previously given value of @code{CFLAGS}.  The @code{override} directive is
used so that the new value is assigned even if the previous value of
@code{CFLAGS} was specified with a command argument (@pxref{Override
Directive, , The @code{override} Directive}).

@node File Name Functions, Foreach Function, Text Functions, Functions
@section Functions for File Names
@cindex functions, for file names
@cindex file name functions

Several of the built-in expansion functions relate specifically to
taking apart file names or lists of file names.

Each of the following functions performs a specific transformation on a
file name.  The argument of the function is regarded as a series of file
names, separated by whitespace.  (Leading and trailing whitespace is
ignored.)  Each file name in the series is transformed in the same way and
the results are concatenated with single spaces between them.

@table @code
@item $(dir @var{names}@dots{})
@findex dir
@cindex directory part
@cindex file name, directory part
Extracts the directory-part of each file name in @var{names}.  The
directory-part of the file name is everything up through (and
including) the last slash in it.  If the file name contains no slash,
the directory part is the string @samp{./}.  For example,

@example
$(dir src/foo.c hacks)
@end example

@noindent
produces the result @samp{src/ ./}.

@item $(notdir @var{names}@dots{})
@findex notdir
@cindex file name, nondirectory part
@cindex nondirectory part
Extracts all but the directory-part of each file name in @var{names}.
If the file name contains no slash, it is left unchanged.  Otherwise,
everything through the last slash is removed from it.

A file name that ends with a slash becomes an empty string.  This is
unfortunate, because it means that the result does not always have the
same number of whitespace-separated file names as the argument had;
but we do not see any other valid alternative.

For example,

@example
$(notdir src/foo.c hacks)
@end example

@noindent
produces the result @samp{foo.c hacks}.

@item $(suffix @var{names}@dots{})
@findex suffix
@cindex suffix, function to find
@cindex file name suffix
Extracts the suffix of each file name in @var{names}.  If the file name
contains a period, the suffix is everything starting with the last
period.  Otherwise, the suffix is the empty string.  This frequently
means that the result will be empty when @var{names} is not, and if
@var{names} contains multiple file names, the result may contain fewer
file names.

For example,

@example
$(suffix src/foo.c src-1.0/bar.c hacks)
@end example

@noindent
produces the result @samp{.c .c}.

@item $(basename @var{names}@dots{})
@findex basename
@cindex basename
@cindex file name, basename of
Extracts all but the suffix of each file name in @var{names}.  If the
file name contains a period, the basename is everything starting up to
(and not including) the last period.  Periods in the directory part are
ignored.  If there is no period, the basename is the entire file name.
For example,

@example
$(basename src/foo.c src-1.0/bar hacks)
@end example

@noindent
produces the result @samp{src/foo src-1.0/bar hacks}.

@c plural convention with dots (be consistent)
@item $(addsuffix @var{suffix},@var{names}@dots{})
@findex addsuffix
@cindex suffix, adding
@cindex file name suffix, adding
The argument @var{names} is regarded as a series of names, separated
by whitespace; @var{suffix} is used as a unit.  The value of
@var{suffix} is appended to the end of each individual name and the
resulting larger names are concatenated with single spaces between
them.  For example,

@example
$(addsuffix .c,foo bar)
@end example

@noindent
produces the result @samp{foo.c bar.c}.

@item $(addprefix @var{prefix},@var{names}@dots{})
@findex addprefix
@cindex prefix, adding
@cindex file name prefix, adding
The argument @var{names} is regarded as a series of names, separated
by whitespace; @var{prefix} is used as a unit.  The value of
@var{prefix} is prepended to the front of each individual name and the
resulting larger names are concatenated with single spaces between
them.  For example,

@example
$(addprefix src/,foo bar)
@end example

@noindent
produces the result @samp{src/foo src/bar}.

@item $(join @var{list1},@var{list2})
@findex join
@cindex joining lists of words
@cindex words, joining lists
Concatenates the two arguments word by word: the two first words (one
from each argument) concatenated form the first word of the result, the
two second words form the second word of the result, and so on.  So the
@var{n}th word of the result comes from the @var{n}th word of each
argument.  If one argument has more words that the other, the extra
words are copied unchanged into the result.

For example, @samp{$(join a b,.c .o)} produces @samp{a.c b.o}.

Whitespace between the words in the lists is not preserved; it is
replaced with a single space.

This function can merge the results of the @code{dir} and
@code{notdir} functions, to produce the original list of files which
was given to those two functions.@refill

@item $(word @var{n},@var{text})
@findex word
@cindex word, selecting a
@cindex selecting a word
Returns the @var{n}th word of @var{text}.  The legitimate values of
@var{n} start from 1.  If @var{n} is bigger than the number of words
in @var{text}, the value is empty.  For example,

@example
$(word 2, foo bar baz)
@end example

@noindent
returns @samp{bar}.

@item $(wordlist @var{s},@var{e},@var{text})
@findex wordlist
@cindex words, selecting lists of
@cindex selecting word lists
Returns the list of words in @var{text} starting with word @var{s} and
ending with word @var{e} (inclusive).  The legitimate values of @var{s}
and @var{e} start from 1.  If @var{s} is bigger than the number of words
in @var{text}, the value is empty.  If @var{e} is bigger than the number
of words in @var{text}, words up to the end of @var{text} are returned.
If @var{s} is greater than @var{e}, nothing is returned.  For example,

@example
$(wordlist 2, 3, foo bar baz)
@end example

@noindent
returns @samp{bar baz}.

@c Following item phrased to prevent overfull hbox.  --RJC 17 Jul 92
@item $(words @var{text})
@findex words
@cindex words, finding number
Returns the number of words in @var{text}.
Thus, the last word of @var{text} is
@w{@code{$(word $(words @var{text}),@var{text})}}.@refill

@item $(firstword @var{names}@dots{})
@findex firstword
@cindex words, extracting first
The argument @var{names} is regarded as a series of names, separated
by whitespace.  The value is the first name in the series.  The rest
of the names are ignored.

For example,

@example
$(firstword foo bar)
@end example

@noindent
produces the result @samp{foo}.  Although @code{$(firstword
@var{text})} is the same as @code{$(word 1,@var{text})}, the
@code{firstword} function is retained for its simplicity.@refill

@item $(wildcard @var{pattern})
@findex wildcard
@cindex wildcard, function
The argument @var{pattern} is a file name pattern, typically containing
wildcard characters (as in shell file name patterns).  The result of
@code{wildcard} is a space-separated list of the names of existing files
that match the pattern.
@xref{Wildcards, ,Using Wildcard Characters in File Names}.
@end table

@node Foreach Function, If Function, File Name Functions, Functions
@section The @code{foreach} Function
@findex foreach
@cindex words, iterating over

The @code{foreach} function is very different from other functions.  It
causes one piece of text to be used repeatedly, each time with a different
substitution performed on it.  It resembles the @code{for} command in the
shell @code{sh} and the @code{foreach} command in the C-shell @code{csh}.

The syntax of the @code{foreach} function is:

@example
$(foreach @var{var},@var{list},@var{text})
@end example

@noindent
The first two arguments, @var{var} and @var{list}, are expanded before
anything else is done; note that the last argument, @var{text}, is
@strong{not} expanded at the same time.  Then for each word of the expanded
value of @var{list}, the variable named by the expanded value of @var{var}
is set to that word, and @var{text} is expanded.  Presumably @var{text}
contains references to that variable, so its expansion will be different
each time.

The result is that @var{text} is expanded as many times as there are
whitespace-separated words in @var{list}.  The multiple expansions of
@var{text} are concatenated, with spaces between them, to make the result
of @code{foreach}.

This simple example sets the variable @samp{files} to the list of all files
in the directories in the list @samp{dirs}:

@example
dirs := a b c d
files := $(foreach dir,$(dirs),$(wildcard $(dir)/*))
@end example

Here @var{text} is @samp{$(wildcard $(dir)/*)}.  The first repetition
finds the value @samp{a} for @code{dir}, so it produces the same result
as @samp{$(wildcard a/*)}; the second repetition produces the result
of @samp{$(wildcard b/*)}; and the third, that of @samp{$(wildcard c/*)}.

This example has the same result (except for setting @samp{dirs}) as
the following example:

@example
files := $(wildcard a/* b/* c/* d/*)
@end example

When @var{text} is complicated, you can improve readability by giving it
a name, with an additional variable:

@example
find_files = $(wildcard $(dir)/*)
dirs := a b c d
files := $(foreach dir,$(dirs),$(find_files))
@end example

@noindent
Here we use the variable @code{find_files} this way.  We use plain @samp{=}
to define a recursively-expanding variable, so that its value contains an
actual function call to be reexpanded under the control of @code{foreach};
a simply-expanded variable would not do, since @code{wildcard} would be
called only once at the time of defining @code{find_files}.

The @code{foreach} function has no permanent effect on the variable
@var{var}; its value and flavor after the @code{foreach} function call are
the same as they were beforehand.  The other values which are taken from
@var{list} are in effect only temporarily, during the execution of
@code{foreach}.  The variable @var{var} is a simply-expanded variable
during the execution of @code{foreach}.  If @var{var} was undefined
before the @code{foreach} function call, it is undefined after the call.
@xref{Flavors, ,The Two Flavors of Variables}.@refill

You must take care when using complex variable expressions that result in
variable names because many strange things are valid variable names, but
are probably not what you intended.  For example,

@smallexample
files := $(foreach Esta escrito en espanol!,b c ch,$(find_files))
@end smallexample

@noindent
might be useful if the value of @code{find_files} references the variable
whose name is @samp{Esta escrito en espanol!} (es un nombre bastante largo,
no?), but it is more likely to be a mistake.

@node If Function, Call Function, Foreach Function, Functions
@section The @code{if} Function
@findex if
@cindex conditional expansion

The @code{if} function provides support for conditional expansion in a
functional context (as opposed to the GNU @code{make} makefile
conditionals such as @code{ifeq} (@pxref{Conditional Syntax, ,Syntax of
Conditionals}).

An @code{if} function call can contain either two or three arguments:

@example
$(if @var{condition},@var{then-part}[,@var{else-part}])
@end example

The first argument, @var{condition}, first has all preceding and
trailing whitespace stripped, then is expanded.  If it expands to any
non-empty string, then the condition is considered to be true.  If it
expands to an empty string, the condition is considered to be false.

If the condition is true then the second argument, @var{then-part}, is
evaluated and this is used as the result of the evaluation of the entire
@code{if} function.

If the condition is false then the third argument, @var{else-part}, is
evaluated and this is the result of the @code{if} function.  If there is
no third argument, the @code{if} function evaluates to nothing (the
empty string).

Note that only one of the @var{then-part} or the @var{else-part} will be
evaluated, never both.  Thus, either can contain side-effects (such as
@code{shell} function calls, etc.)

@node Call Function, Origin Function, If Function, Functions
@section The @code{call} Function
@findex call
@cindex functions, user defined
@cindex user defined functions

The @code{call} function is unique in that it can be used to create new
parameterized functions.  You can write a complex expression as the
value of a variable, then use @code{call} to expand it with different
values.

The syntax of the @code{call} function is:

@example
$(call @var{variable},@var{param},@var{param},@dots{})
@end example

When @code{make} expands this function, it assigns each @var{param} to
temporary variables @code{$(1)}, @code{$(2)}, etc.  The variable
@code{$(0)} will contain @var{variable}.  There is no maximum number of
parameter arguments.  There is no minimum, either, but it doesn't make
sense to use @code{call} with no parameters.

Then @var{variable} is expanded as a @code{make} variable in the context
of these temporary assignments.  Thus, any reference to @code{$(1)} in
the value of @var{variable} will resolve to the first @var{param} in the
invocation of @code{call}.

Note that @var{variable} is the @emph{name} of a variable, not a
@emph{reference} to that variable.  Therefore you would not normally use
a @samp{$} or parentheses when writing it.  (You can, however, use a
variable reference in the name if you want the name not to be a
constant.)

If @var{variable} is the name of a builtin function, the builtin function
is always invoked (even if a @code{make} variable by that name also
exists).

The @code{call} function expands the @var{param} arguments before
assigning them to temporary variables.  This means that @var{variable}
values containing references to builtin functions that have special
expansion rules, like @code{foreach} or @code{if}, may not work as you
expect.

Some examples may make this clearer.

This macro simply reverses its arguments:

@smallexample
reverse = $(2) $(1)

foo = $(call reverse,a,b)
@end smallexample

@noindent
Here @var{foo} will contain @samp{b a}.

This one is slightly more interesting: it defines a macro to search for
the first instance of a program in @code{PATH}:

@smallexample
pathsearch = $(firstword $(wildcard $(addsufix /$(1),$(subst :, ,$(PATH)))))

LS := $(call pathsearch,ls)
@end smallexample

@noindent
Now the variable LS contains @code{/bin/ls} or similar.

The @code{call} function can be nested.  Each recursive invocation gets
its own local values for @code{$(1)}, etc. that mask the values of
higher-level @code{call}.  For example, here is an implementation of a
@dfn{map} function:

@smallexample
map = $(foreach a,$(2),$(call $(1),$(a)))
@end smallexample

Now you can @var{map} a function that normally takes only one argument,
such as @code{origin}, to multiple values in one step:

@smallexample
o = $(call map,origin,o map MAKE)
@end smallexample

and end up with @var{o} containing something like @samp{file file default}.

A final caution: be careful when adding whitespace to the arguments to
@code{call}.  As with other functions, any whitespace contained in the
second and subsequent arguments is kept; this can cause strange
effects.  It's generally safest to remove all extraneous whitespace when
providing parameters to @code{call}.


@node Origin Function, Shell Function, Call Function, Functions
@section The @code{origin} Function
@findex origin
@cindex variables, origin of
@cindex origin of variable

The @code{origin} function is unlike most other functions in that it does
not operate on the values of variables; it tells you something @emph{about}
a variable.  Specifically, it tells you where it came from.

The syntax of the @code{origin} function is:

@example
$(origin @var{variable})
@end example

Note that @var{variable} is the @emph{name} of a variable to inquire about;
not a @emph{reference} to that variable.  Therefore you would not normally
use a @samp{$} or parentheses when writing it.  (You can, however, use a
variable reference in the name if you want the name not to be a constant.)

The result of this function is a string telling you how the variable
@var{variable} was defined:

@table @samp
@item undefined

if @var{variable} was never defined.

@item default

if @var{variable} has a default definition, as is usual with @code{CC}
and so on.  @xref{Implicit Variables, ,Variables Used by Implicit Rules}.
Note that if you have redefined a default variable, the @code{origin}
function will return the origin of the later definition.

@item environment

if @var{variable} was defined as an environment variable and the
@samp{-e} option is @emph{not} turned on (@pxref{Options Summary, ,Summary of Options}).

@item environment override

if @var{variable} was defined as an environment variable and the
@w{@samp{-e}} option @emph{is} turned on (@pxref{Options Summary,
,Summary of Options}).@refill

@item file

if @var{variable} was defined in a makefile.

@item command line

if @var{variable} was defined on the command line.

@item override

if @var{variable} was defined with an @code{override} directive in a
makefile (@pxref{Override Directive, ,The @code{override} Directive}).

@item automatic

if @var{variable} is an automatic variable defined for the
execution of the commands for each rule
(@pxref{Automatic, , Automatic Variables}).
@end table

This information is primarily useful (other than for your curiosity) to
determine if you want to believe the value of a variable.  For example,
suppose you have a makefile @file{foo} that includes another makefile
@file{bar}.  You want a variable @code{bletch} to be defined in @file{bar}
if you run the command @w{@samp{make -f bar}}, even if the environment contains
a definition of @code{bletch}.  However, if @file{foo} defined
@code{bletch} before including @file{bar}, you do not want to override that
definition.  This could be done by using an @code{override} directive in
@file{foo}, giving that definition precedence over the later definition in
@file{bar}; unfortunately, the @code{override} directive would also
override any command line definitions.  So, @file{bar} could
include:@refill

@example
@group
ifdef bletch
ifeq "$(origin bletch)" "environment"
bletch = barf, gag, etc.
endif
endif
@end group
@end example

@noindent
If @code{bletch} has been defined from the environment, this will redefine
it.

If you want to override a previous definition of @code{bletch} if it came
from the environment, even under @samp{-e}, you could instead write:

@example
@group
ifneq "$(findstring environment,$(origin bletch))" ""
bletch = barf, gag, etc.
endif
@end group
@end example

Here the redefinition takes place if @samp{$(origin bletch)} returns either
@samp{environment} or @samp{environment override}.
@xref{Text Functions, , Functions for String Substitution and Analysis}.

@node Shell Function, Make Control Functions, Origin Function, Functions
@section The @code{shell} Function
@findex shell
@cindex commands, expansion
@cindex backquotes
@cindex shell command, function for

The @code{shell} function is unlike any other function except the
@code{wildcard} function
(@pxref{Wildcard Function, ,The Function @code{wildcard}}) in that it
communicates with the world outside of @code{make}.

The @code{shell} function performs the same function that backquotes
(@samp{`}) perform in most shells: it does @dfn{command expansion}.  This
means that it takes an argument that is a shell command and returns the
output of the command.  The only processing @code{make} does on the result,
before substituting it into the surrounding text, is to convert each
newline or carriage-return / newline pair to a single space.  It also
removes the trailing (carriage-return and) newline, if it's the last
thing in the result.@refill

The commands run by calls to the @code{shell} function are run when the
function calls are expanded.  In most cases, this is when the makefile is
read in.  The exception is that function calls in the commands of the rules
are expanded when the commands are run, and this applies to @code{shell}
function calls like all others.

Here are some examples of the use of the @code{shell} function:

@example
contents := $(shell cat foo)
@end example

@noindent
sets @code{contents} to the contents of the file @file{foo}, with a space
(rather than a newline) separating each line.

@example
files := $(shell echo *.c)
@end example

@noindent
sets @code{files} to the expansion of @samp{*.c}.  Unless @code{make} is
using a very strange shell, this has the same result as
@w{@samp{$(wildcard *.c)}}.@refill

@node Make Control Functions,  , Shell Function, Functions
@section Functions That Control Make
@cindex functions, for controlling make
@cindex controlling make

These functions control the way make runs.  Generally, they are used to
provide information to the user of the makefile or to cause make to stop
if some sort of environmental error is detected.

@table @code
@item $(error @var{text}@dots{})
@findex error
@cindex error, stopping on
@cindex stopping make
Generates a fatal error where the message is @var{text}.  Note that the
error is generated whenever this function is evaluated.  So, if you put
it inside a command script or on the right side of a recursive variable
assignment, it won't be evaluated until later.  The @var{text} will be
expanded before the error is generated.

For example,

@example
ifdef ERROR1
$(error error is $(ERROR1))
endif
@end example

@noindent
will generate a fatal error during the read of the makefile if the
@code{make} variable @code{ERROR1} is defined.  Or,

@example
ERR = $(error found an error!)

.PHONY: err
err: ; $(ERR)
@end example

@noindent
will generate a fatal error while @code{make} is running, if the
@code{err} target is invoked.

@item $(warning @var{text}@dots{})
@findex warning
@cindex warnings, printing
@cindex printing user warnings
This function works similarly to the @code{error} function, above,
except that @code{make} doesn't exit.  Instead, @var{text} is expanded
and the resulting message is displayed, but processing of the makefile
continues.

The result of the expansion of this function is the empty string.
@end table

@node Running, Implicit Rules, Functions, Top
@chapter How to Run @code{make}

A makefile that says how to recompile a program can be used in more
than one way.  The simplest use is to recompile every file that is out
of date.  Usually, makefiles are written so that if you run
@code{make} with no arguments, it does just that.

But you might want to update only some of the files; you might want to use
a different compiler or different compiler options; you might want just to
find out which files are out of date without changing them.

By giving arguments when you run @code{make}, you can do any of these
things and many others.

The exit status of @code{make} is always one of three values:
@table @code
@item 0
The exit status is zero if @code{make} is successful.
@item 2
The exit status is two if @code{make} encounters any errors.
It will print messages describing the particular errors.
@item 1
The exit status is one if you use the @samp{-q} flag and @code{make}
determines that some target is not already up to date.
@xref{Instead of Execution, ,Instead of Executing the Commands}.
@end table

@menu
* Makefile Arguments::          How to specify which makefile to use.
* Goals::                       How to use goal arguments to specify which
                                  parts of the makefile to use.
* Instead of Execution::        How to use mode flags to specify what
                                  kind of thing to do with the commands
                                  in the makefile other than simply
                                  execute them.
* Avoiding Compilation::        How to avoid recompiling certain files.
* Overriding::                  How to override a variable to specify
                                  an alternate compiler and other things.
* Testing::                     How to proceed past some errors, to
                                  test compilation.
* Options Summary::             Summary of Options
@end menu

@node Makefile Arguments, Goals,  , Running
@section Arguments to Specify the Makefile
@cindex @code{--file}
@cindex @code{--makefile}
@cindex @code{-f}

The way to specify the name of the makefile is with the @samp{-f} or
@samp{--file} option (@samp{--makefile} also works).  For example,
@samp{-f altmake} says to use the file @file{altmake} as the makefile.

If you use the @samp{-f} flag several times and follow each @samp{-f}
with an argument, all the specified files are used jointly as
makefiles.

If you do not use the @samp{-f} or @samp{--file} flag, the default is
to try @file{GNUmakefile}, @file{makefile}, and @file{Makefile}, in
that order, and use the first of these three which exists or can be made
(@pxref{Makefiles, ,Writing Makefiles}).@refill

@node Goals, Instead of Execution, Makefile Arguments, Running
@section Arguments to Specify the Goals
@cindex goal, how to specify

The @dfn{goals} are the targets that @code{make} should strive ultimately
to update.  Other targets are updated as well if they appear as
prerequisites of goals, or prerequisites of prerequisites of goals, etc.

By default, the goal is the first target in the makefile (not counting
targets that start with a period).  Therefore, makefiles are usually
written so that the first target is for compiling the entire program or
programs they describe.  If the first rule in the makefile has several
targets, only the first target in the rule becomes the default goal, not
the whole list.

You can specify a different goal or goals with arguments to @code{make}.
Use the name of the goal as an argument.  If you specify several goals,
@code{make} processes each of them in turn, in the order you name them.

Any target in the makefile may be specified as a goal (unless it
starts with @samp{-} or contains an @samp{=}, in which case it will be
parsed as a switch or variable definition, respectively).  Even
targets not in the makefile may be specified, if @code{make} can find
implicit rules that say how to make them.

@cindex @code{MAKECMDGOALS}
@vindex MAKECMDGOALS
@code{Make} will set the special variable @code{MAKECMDGOALS} to the
list of goals you specified on the command line.  If no goals were given
on the command line, this variable is empty.  Note that this variable
should be used only in special circumstances.

An example of appropriate use is to avoid including @file{.d} files
during @code{clean} rules (@pxref{Automatic Prerequisites}), so
@code{make} won't create them only to immediately remove them
again:@refill

@example
@group
sources = foo.c bar.c

ifneq ($(MAKECMDGOALS),clean)
include $(sources:.c=.d)
endif
@end group
@end example

One use of specifying a goal is if you want to compile only a part of
the program, or only one of several programs.  Specify as a goal each
file that you wish to remake.  For example, consider a directory containing
several programs, with a makefile that starts like this:

@example
.PHONY: all
all: size nm ld ar as
@end example

If you are working on the program @code{size}, you might want to say
@w{@samp{make size}} so that only the files of that program are recompiled.

Another use of specifying a goal is to make files that are not normally
made.  For example, there may be a file of debugging output, or a
version of the program that is compiled specially for testing, which has
a rule in the makefile but is not a prerequisite of the default goal.

Another use of specifying a goal is to run the commands associated with
a phony target (@pxref{Phony Targets}) or empty target (@pxref{Empty
Targets, ,Empty Target Files to Record Events}).  Many makefiles contain
a phony target named @file{clean} which deletes everything except source
files.  Naturally, this is done only if you request it explicitly with
@w{@samp{make clean}}.  Following is a list of typical phony and empty
target names.  @xref{Standard Targets}, for a detailed list of all the
standard target names which GNU software packages use.

@table @file
@item all
@cindex @code{all} @r{(standard target)}
Make all the top-level targets the makefile knows about.

@item clean
@cindex @code{clean} @r{(standard target)}
Delete all files that are normally created by running @code{make}.

@item mostlyclean
@cindex @code{mostlyclean} @r{(standard target)}
Like @samp{clean}, but may refrain from deleting a few files that people
normally don't want to recompile.  For example, the @samp{mostlyclean}
target for GCC does not delete @file{libgcc.a}, because recompiling it
is rarely necessary and takes a lot of time.

@item distclean
@cindex @code{distclean} @r{(standard target)}
@itemx realclean
@cindex @code{realclean} @r{(standard target)}
@itemx clobber
@cindex @code{clobber} @r{(standard target)}
Any of these targets might be defined to delete @emph{more} files than
@samp{clean} does.  For example, this would delete configuration files
or links that you would normally create as preparation for compilation,
even if the makefile itself cannot create these files.

@item install
@cindex @code{install} @r{(standard target)}
Copy the executable file into a directory that users typically search
for commands; copy any auxiliary files that the executable uses into
the directories where it will look for them.

@item print
@cindex @code{print} @r{(standard target)}
Print listings of the source files that have changed.

@item tar
@cindex @code{tar} @r{(standard target)}
Create a tar file of the source files.

@item shar
@cindex @code{shar} @r{(standard target)}
Create a shell archive (shar file) of the source files.

@item dist
@cindex @code{dist} @r{(standard target)}
Create a distribution file of the source files.  This might
be a tar file, or a shar file, or a compressed version of one of the
above, or even more than one of the above.

@item TAGS
@cindex @code{TAGS} @r{(standard target)}
Update a tags table for this program.

@item check
@cindex @code{check} @r{(standard target)}
@itemx test
@cindex @code{test} @r{(standard target)}
Perform self tests on the program this makefile builds.
@end table

@node Instead of Execution, Avoiding Compilation, Goals, Running
@section Instead of Executing the Commands
@cindex execution, instead of
@cindex commands, instead of executing

The makefile tells @code{make} how to tell whether a target is up to date,
and how to update each target.  But updating the targets is not always
what you want.  Certain options specify other activities for @code{make}.

@comment Extra blank lines make it print better.
@table @samp
@item -n
@itemx --just-print
@itemx --dry-run
@itemx --recon
@cindex @code{--just-print}
@cindex @code{--dry-run}
@cindex @code{--recon}
@cindex @code{-n}

``No-op''.  The activity is to print what commands would be used to make
the targets up to date, but not actually execute them.

@item -t
@itemx --touch
@cindex @code{--touch}
@cindex touching files
@cindex target, touching
@cindex @code{-t}

``Touch''.  The activity is to mark the targets as up to date without
actually changing them.  In other words, @code{make} pretends to compile
the targets but does not really change their contents.

@item -q
@itemx --question
@cindex @code{--question}
@cindex @code{-q}
@cindex question mode

``Question''.  The activity is to find out silently whether the targets
are up to date already; but execute no commands in either case.  In other
words, neither compilation nor output will occur.

@item -W @var{file}
@itemx --what-if=@var{file}
@itemx --assume-new=@var{file}
@itemx --new-file=@var{file}
@cindex @code{--what-if}
@cindex @code{-W}
@cindex @code{--assume-new}
@cindex @code{--new-file}
@cindex what if
@cindex files, assuming new

``What if''.  Each @samp{-W} flag is followed by a file name.  The given
files' modification times are recorded by @code{make} as being the present
time, although the actual modification times remain the same.
You can use the @samp{-W} flag in conjunction with the @samp{-n} flag
to see what would happen if you were to modify specific files.@refill
@end table

With the @samp{-n} flag, @code{make} prints the commands that it would
normally execute but does not execute them.

With the @samp{-t} flag, @code{make} ignores the commands in the rules
and uses (in effect) the command @code{touch} for each target that needs to
be remade.  The @code{touch} command is also printed, unless @samp{-s} or
@code{.SILENT} is used.  For speed, @code{make} does not actually invoke
the program @code{touch}.  It does the work directly.

With the @samp{-q} flag, @code{make} prints nothing and executes no
commands, but the exit status code it returns is zero if and only if the
targets to be considered are already up to date.  If the exit status is
one, then some updating needs to be done.  If @code{make} encounters an
error, the exit status is two, so you can distinguish an error from a
target that is not up to date.

It is an error to use more than one of these three flags in the same
invocation of @code{make}.

The @samp{-n}, @samp{-t}, and @samp{-q} options do not affect command
lines that begin with @samp{+} characters or contain the strings
@samp{$(MAKE)} or @samp{$@{MAKE@}}.  Note that only the line containing
the @samp{+} character or the strings @samp{$(MAKE)} or @samp{$@{MAKE@}}
is run regardless of these options.  Other lines in the same rule are
not run unless they too begin with @samp{+} or contain @samp{$(MAKE)} or
@samp{$@{MAKE@}} (@xref{MAKE Variable, ,How the @code{MAKE} Variable Works}.)

The @samp{-W} flag provides two features:

@itemize @bullet
@item
If you also use the @samp{-n} or @samp{-q} flag, you can see what
@code{make} would do if you were to modify some files.

@item
Without the @samp{-n} or @samp{-q} flag, when @code{make} is actually
executing commands, the @samp{-W} flag can direct @code{make} to act
as if some files had been modified, without actually modifying the
files.@refill
@end itemize

Note that the options @samp{-p} and @samp{-v} allow you to obtain other
information about @code{make} or about the makefiles in use
(@pxref{Options Summary, ,Summary of Options}).@refill

@node Avoiding Compilation, Overriding, Instead of Execution, Running
@section Avoiding Recompilation of Some Files
@cindex @code{-o}
@cindex @code{--old-file}
@cindex @code{--assume-old}
@cindex files, assuming old
@cindex files, avoiding recompilation of
@cindex recompilation, avoiding

Sometimes you may have changed a source file but you do not want to
recompile all the files that depend on it.  For example, suppose you add
a macro or a declaration to a header file that many other files depend
on.  Being conservative, @code{make} assumes that any change in the
header file requires recompilation of all dependent files, but you know
that they do not need to be recompiled and you would rather not waste
the time waiting for them to compile.

If you anticipate the problem before changing the header file, you can
use the @samp{-t} flag.  This flag tells @code{make} not to run the
commands in the rules, but rather to mark the target up to date by
changing its last-modification date.  You would follow this procedure:

@enumerate
@item
Use the command @samp{make} to recompile the source files that really
need recompilation.

@item
Make the changes in the header files.

@item
Use the command @samp{make -t} to mark all the object files as
up to date.  The next time you run @code{make}, the changes in the
header files will not cause any recompilation.
@end enumerate

If you have already changed the header file at a time when some files
do need recompilation, it is too late to do this.  Instead, you can
use the @w{@samp{-o @var{file}}} flag, which marks a specified file as
``old'' (@pxref{Options Summary, ,Summary of Options}).  This means
that the file itself will not be remade, and nothing else will be
remade on its account.  Follow this procedure:

@enumerate
@item
Recompile the source files that need compilation for reasons independent
of the particular header file, with @samp{make -o @var{headerfile}}.
If several header files are involved, use a separate @samp{-o} option
for each header file.

@item
Touch all the object files with @samp{make -t}.
@end enumerate

@node Overriding, Testing, Avoiding Compilation, Running
@section Overriding Variables
@cindex overriding variables with arguments
@cindex variables, overriding with arguments
@cindex command line variables
@cindex variables, command line

An argument that contains @samp{=} specifies the value of a variable:
@samp{@var{v}=@var{x}} sets the value of the variable @var{v} to @var{x}.
If you specify a value in this way, all ordinary assignments of the same
variable in the makefile are ignored; we say they have been
@dfn{overridden} by the command line argument.

The most common way to use this facility is to pass extra flags to
compilers.  For example, in a properly written makefile, the variable
@code{CFLAGS} is included in each command that runs the C compiler, so a
file @file{foo.c} would be compiled something like this:

@example
cc -c $(CFLAGS) foo.c
@end example

Thus, whatever value you set for @code{CFLAGS} affects each compilation
that occurs.  The makefile probably specifies the usual value for
@code{CFLAGS}, like this:

@example
CFLAGS=-g
@end example

Each time you run @code{make}, you can override this value if you
wish.  For example, if you say @samp{make CFLAGS='-g -O'}, each C
compilation will be done with @samp{cc -c -g -O}.  (This illustrates
how you can use quoting in the shell to enclose spaces and other
special characters in the value of a variable when you override it.)

The variable @code{CFLAGS} is only one of many standard variables that
exist just so that you can change them this way.  @xref{Implicit
Variables, , Variables Used by Implicit Rules}, for a complete list.

You can also program the makefile to look at additional variables of your
own, giving the user the ability to control other aspects of how the
makefile works by changing the variables.

When you override a variable with a command argument, you can define either
a recursively-expanded variable or a simply-expanded variable.  The
examples shown above make a recursively-expanded variable; to make a
simply-expanded variable, write @samp{:=} instead of @samp{=}.  But, unless
you want to include a variable reference or function call in the
@emph{value} that you specify, it makes no difference which kind of
variable you create.

There is one way that the makefile can change a variable that you have
overridden.  This is to use the @code{override} directive, which is a line
that looks like this: @samp{override @var{variable} = @var{value}}
(@pxref{Override Directive, ,The @code{override} Directive}).

@node Testing, Options Summary, Overriding, Running
@section Testing the Compilation of a Program
@cindex testing compilation
@cindex compilation, testing

Normally, when an error happens in executing a shell command, @code{make}
gives up immediately, returning a nonzero status.  No further commands are
executed for any target.  The error implies that the goal cannot be
correctly remade, and @code{make} reports this as soon as it knows.

When you are compiling a program that you have just changed, this is not
what you want.  Instead, you would rather that @code{make} try compiling
every file that can be tried, to show you as many compilation errors
as possible.

@cindex @code{-k}
@cindex @code{--keep-going}
On these occasions, you should use the @samp{-k} or
@samp{--keep-going} flag.  This tells @code{make} to continue to
consider the other prerequisites of the pending targets, remaking them
if necessary, before it gives up and returns nonzero status.  For
example, after an error in compiling one object file, @samp{make -k}
will continue compiling other object files even though it already
knows that linking them will be impossible.  In addition to continuing
after failed shell commands, @samp{make -k} will continue as much as
possible after discovering that it does not know how to make a target
or prerequisite file.  This will always cause an error message, but
without @samp{-k}, it is a fatal error (@pxref{Options Summary,
,Summary of Options}).@refill

The usual behavior of @code{make} assumes that your purpose is to get the
goals up to date; once @code{make} learns that this is impossible, it might
as well report the failure immediately.  The @samp{-k} flag says that the
real purpose is to test as much as possible of the changes made in the
program, perhaps to find several independent problems so that you can
correct them all before the next attempt to compile.  This is why Emacs'
@kbd{M-x compile} command passes the @samp{-k} flag by default.

@node Options Summary,  , Testing, Running
@section Summary of Options
@cindex options
@cindex flags
@cindex switches

Here is a table of all the options @code{make} understands:

@table @samp
@item -b
@cindex @code{-b}
@itemx -m
@cindex @code{-m}
These options are ignored for compatibility with other versions of @code{make}.

@item -C @var{dir}
@cindex @code{-C}
@itemx --directory=@var{dir}
@cindex @code{--directory}
Change to directory @var{dir} before reading the makefiles.  If multiple
@samp{-C} options are specified, each is interpreted relative to the
previous one: @samp{-C / -C etc} is equivalent to @samp{-C /etc}.
This is typically used with recursive invocations of @code{make}
(@pxref{Recursion, ,Recursive Use of @code{make}}).

@item -d
@cindex @code{-d}
@c Extra blank line here makes the table look better.

Print debugging information in addition to normal processing.  The
debugging information says which files are being considered for
remaking, which file-times are being compared and with what results,
which files actually need to be remade, which implicit rules are
considered and which are applied---everything interesting about how
@code{make} decides what to do.  The @code{-d} option is equivalent to
@samp{--debug=a} (see below).

@item --debug[=@var{options}]
@cindex @code{--debug}
@c Extra blank line here makes the table look better.

Print debugging information in addition to normal processing.  Various
levels and types of output can be chosen.  With no arguments, print the
``basic'' level of debugging.  Possible arguments are below; only the
first character is considered, and values must be comma- or
space-separated.

@table @code
@item a (@i{all})
All types of debugging output is enabled.  This is equivalent to using
@samp{-d}.

@item b (@i{basic})
Basic debugging prints each target that was found to be out-of-date, and
whether the build was successful or not.

@item v (@i{verbose})
A level above @samp{basic}; includes messages about which makefiles were
parsed, prerequisites that did not need to be rebuilt, etc.  This option
also enables @samp{basic} messages.

@item i (@i{implicit})
Prints messages describing the implicit rule searches for each target.
This option also enables @samp{basic} messages.

@item j (@i{jobs})
Prints messages giving details on the invocation of specific subcommands.

@item m (@i{makefile})
By default, the above messages are not enabled while trying to remake
the makefiles.  This option enables messages while rebuilding makefiles,
too.  Note that the @samp{all} option does enable this option.  This
option also enables @samp{basic} messages.
@end table

@item -e
@cindex @code{-e}
@itemx --environment-overrides
@cindex @code{--environment-overrides}
Give variables taken from the environment precedence
over variables from makefiles.
@xref{Environment, ,Variables from the Environment}.

@item -f @var{file}
@cindex @code{-f}
@itemx --file=@var{file}
@cindex @code{--file}
@itemx --makefile=@var{file}
@cindex @code{--makefile}
Read the file named @var{file} as a makefile.
@xref{Makefiles, ,Writing Makefiles}.

@item -h
@cindex @code{-h}
@itemx --help
@cindex @code{--help}
@c Extra blank line here makes the table look better.

Remind you of the options that @code{make} understands and then exit.

@item -i
@cindex @code{-i}
@itemx --ignore-errors
@cindex @code{--ignore-errors}
Ignore all errors in commands executed to remake files.
@xref{Errors, ,Errors in Commands}.

@item -I @var{dir}
@cindex @code{-I}
@itemx --include-dir=@var{dir}
@cindex @code{--include-dir}
Specifies a directory @var{dir} to search for included makefiles.
@xref{Include, ,Including Other Makefiles}.  If several @samp{-I}
options are used to specify several directories, the directories are
searched in the order specified.

@item -j [@var{jobs}]
@cindex @code{-j}
@itemx --jobs[=@var{jobs}]
@cindex @code{--jobs}
Specifies the number of jobs (commands) to run simultaneously.  With no
argument, @code{make} runs as many jobs simultaneously as possible.  If
there is more than one @samp{-j} option, the last one is effective.
@xref{Parallel, ,Parallel Execution},
for more information on how commands are run.
Note that this option is ignored on MS-DOS.

@item -k
@cindex @code{-k}
@itemx --keep-going
@cindex @code{--keep-going}
Continue as much as possible after an error.  While the target that
failed, and those that depend on it, cannot be remade, the other
prerequisites of these targets can be processed all the same.
@xref{Testing, ,Testing the Compilation of a Program}.

@item -l [@var{load}]
@cindex @code{-l}
@itemx --load-average[=@var{load}]
@cindex @code{--load-average}
@itemx --max-load[=@var{load}]
@cindex @code{--max-load}
Specifies that no new jobs (commands) should be started if there are
other jobs running and the load average is at least @var{load} (a
floating-point number).  With no argument, removes a previous load
limit.  @xref{Parallel, ,Parallel Execution}.

@item -n
@cindex @code{-n}
@itemx --just-print
@cindex @code{--just-print}
@itemx --dry-run
@cindex @code{--dry-run}
@itemx --recon
@cindex @code{--recon}
@c Extra blank line here makes the table look better.

Print the commands that would be executed, but do not execute them.
@xref{Instead of Execution, ,Instead of Executing the Commands}.

@item -o @var{file}
@cindex @code{-o}
@itemx --old-file=@var{file}
@cindex @code{--old-file}
@itemx --assume-old=@var{file}
@cindex @code{--assume-old}
Do not remake the file @var{file} even if it is older than its
prerequisites, and do not remake anything on account of changes in
@var{file}.  Essentially the file is treated as very old and its rules
are ignored.  @xref{Avoiding Compilation, ,Avoiding Recompilation of
Some Files}.@refill

@item -p
@cindex @code{-p}
@itemx --print-data-base
@cindex @code{--print-data-base}
@cindex data base of @code{make} rules
@cindex predefined rules and variables, printing
Print the data base (rules and variable values) that results from
reading the makefiles; then execute as usual or as otherwise specified.
This also prints the version information given by the @samp{-v} switch
(see below).  To print the data base without trying to remake any files,
use @w{@samp{make -qp}}.  To print the data base of predefined rules and
variables, use @w{@samp{make -p -f /dev/null}}.  The data base output
contains filename and linenumber information for command and variable
definitions, so it can be a useful debugging tool in complex environments.

@item -q
@cindex @code{-q}
@itemx --question
@cindex @code{--question}
``Question mode''.  Do not run any commands, or print anything; just
return an exit status that is zero if the specified targets are already
up to date, one if any remaking is required, or two if an error is
encountered.  @xref{Instead of Execution, ,Instead of Executing the
Commands}.@refill

@item -r
@cindex @code{-r}
@itemx --no-builtin-rules
@cindex @code{--no-builtin-rules}
Eliminate use of the built-in implicit rules (@pxref{Implicit Rules,
,Using Implicit Rules}).  You can still define your own by writing
pattern rules (@pxref{Pattern Rules, ,Defining and Redefining Pattern
Rules}).  The @samp{-r} option also clears out the default list of
suffixes for suffix rules (@pxref{Suffix Rules, ,Old-Fashioned Suffix
Rules}).  But you can still define your own suffixes with a rule for
@code{.SUFFIXES}, and then define your own suffix rules.  Note that only
@emph{rules} are affected by the @code{-r} option; default variables
remain in effect (@pxref{Implicit Variables, ,Variables Used by Implicit
Rules}); see the @samp{-R} option below.

@item -R
@cindex @code{-R}
@itemx --no-builtin-variables
@cindex @code{--no-builtin-variables}
Eliminate use of the built-in rule-specific variables (@pxref{Implicit
Variables, ,Variables Used by Implicit Rules}).  You can still define
your own, of course.  The @samp{-R} option also automatically enables
the @samp{-r} option (see above), since it doesn't make sense to have
implicit rules without any definitions for the variables that they use.

@item -s
@cindex @code{-s}
@itemx --silent
@cindex @code{--silent}
@itemx --quiet
@cindex @code{--quiet}
@c Extra blank line here makes the table look better.

Silent operation; do not print the commands as they are executed.
@xref{Echoing, ,Command Echoing}.

@item -S
@cindex @code{-S}
@itemx --no-keep-going
@cindex @code{--no-keep-going}
@itemx --stop
@cindex @code{--stop}
@c Extra blank line here makes the table look better.

Cancel the effect of the @samp{-k} option.  This is never necessary
except in a recursive @code{make} where @samp{-k} might be inherited
from the top-level @code{make} via @code{MAKEFLAGS}
(@pxref{Recursion, ,Recursive Use of @code{make}})
or if you set @samp{-k} in @code{MAKEFLAGS} in your environment.@refill

@item -t
@cindex @code{-t}
@itemx --touch
@cindex @code{--touch}
@c Extra blank line here makes the table look better.

Touch files (mark them up to date without really changing them)
instead of running their commands.  This is used to pretend that the
commands were done, in order to fool future invocations of
@code{make}.  @xref{Instead of Execution, ,Instead of Executing the Commands}.

@item -v
@cindex @code{-v}
@itemx --version
@cindex @code{--version}
Print the version of the @code{make} program plus a copyright, a list
of authors, and a notice that there is no warranty; then exit.

@item -w
@cindex @code{-w}
@itemx --print-directory
@cindex @code{--print-directory}
Print a message containing the working directory both before and after
executing the makefile.  This may be useful for tracking down errors
from complicated nests of recursive @code{make} commands.
@xref{Recursion, ,Recursive Use of @code{make}}.  (In practice, you
rarely need to specify this option since @samp{make} does it for you;
see @ref{-w Option, ,The @samp{--print-directory} Option}.)

@itemx --no-print-directory
@cindex @code{--no-print-directory}
Disable printing of the working directory under @code{-w}.
This option is useful when @code{-w} is turned on automatically,
but you do not want to see the extra messages.
@xref{-w Option, ,The @samp{--print-directory} Option}.

@item -W @var{file}
@cindex @code{-W}
@itemx --what-if=@var{file}
@cindex @code{--what-if}
@itemx --new-file=@var{file}
@cindex @code{--new-file}
@itemx --assume-new=@var{file}
@cindex @code{--assume-new}
Pretend that the target @var{file} has just been modified.  When used
with the @samp{-n} flag, this shows you what would happen if you were
to modify that file.  Without @samp{-n}, it is almost the same as
running a @code{touch} command on the given file before running
@code{make}, except that the modification time is changed only in the
imagination of @code{make}.
@xref{Instead of Execution, ,Instead of Executing the Commands}.

@item --warn-undefined-variables
@cindex @code{--warn-undefined-variables}
@cindex variables, warning for undefined
@cindex undefined variables, warning message
Issue a warning message whenever @code{make} sees a reference to an
undefined variable.  This can be helpful when you are trying to debug
makefiles which use variables in complex ways.
@end table

@node Implicit Rules, Archives, Running, Top
@chapter Using Implicit Rules
@cindex implicit rule
@cindex rule, implicit

Certain standard ways of remaking target files are used very often.  For
example, one customary way to make an object file is from a C source file
using the C compiler, @code{cc}.

@dfn{Implicit rules} tell @code{make} how to use customary techniques so
that you do not have to specify them in detail when you want to use
them.  For example, there is an implicit rule for C compilation.  File
names determine which implicit rules are run.  For example, C
compilation typically takes a @file{.c} file and makes a @file{.o} file.
So @code{make} applies the implicit rule for C compilation when it sees
this combination of file name endings.@refill

A chain of implicit rules can apply in sequence; for example, @code{make}
will remake a @file{.o} file from a @file{.y} file by way of a @file{.c} file.
@iftex
@xref{Chained Rules, ,Chains of Implicit Rules}.
@end iftex

The built-in implicit rules use several variables in their commands so
that, by changing the values of the variables, you can change the way the
implicit rule works.  For example, the variable @code{CFLAGS} controls the
flags given to the C compiler by the implicit rule for C compilation.
@iftex
@xref{Implicit Variables, ,Variables Used by Implicit Rules}.
@end iftex

You can define your own implicit rules by writing @dfn{pattern rules}.
@iftex
@xref{Pattern Rules, ,Defining and Redefining Pattern Rules}.
@end iftex

@dfn{Suffix rules} are a more limited way to define implicit rules.
Pattern rules are more general and clearer, but suffix rules are
retained for compatibility.
@iftex
@xref{Suffix Rules, ,Old-Fashioned Suffix Rules}.
@end iftex

@menu
* Using Implicit::              How to use an existing implicit rule
                                  to get the commands for updating a file.
* Catalogue of Rules::          A list of built-in implicit rules.
* Implicit Variables::          How to change what predefined rules do.
* Chained Rules::               How to use a chain of implicit rules.
* Pattern Rules::               How to define new implicit rules.
* Last Resort::                 How to defining commands for rules
                                  which cannot find any.
* Suffix Rules::                The old-fashioned style of implicit rule.
* Implicit Rule Search::        The precise algorithm for applying
                                  implicit rules.
@end menu

@node Using Implicit, Catalogue of Rules,  , Implicit Rules
@section Using Implicit Rules
@cindex implicit rule, how to use
@cindex rule, implicit, how to use

To allow @code{make} to find a customary method for updating a target file,
all you have to do is refrain from specifying commands yourself.  Either
write a rule with no command lines, or don't write a rule at all.  Then
@code{make} will figure out which implicit rule to use based on which
kind of source file exists or can be made.

For example, suppose the makefile looks like this:

@example
foo : foo.o bar.o
        cc -o foo foo.o bar.o $(CFLAGS) $(LDFLAGS)
@end example

@noindent
Because you mention @file{foo.o} but do not give a rule for it, @code{make}
will automatically look for an implicit rule that tells how to update it.
This happens whether or not the file @file{foo.o} currently exists.

If an implicit rule is found, it can supply both commands and one or
more prerequisites (the source files).  You would want to write a rule
for @file{foo.o} with no command lines if you need to specify additional
prerequisites, such as header files, that the implicit rule cannot
supply.

Each implicit rule has a target pattern and prerequisite patterns.  There may
be many implicit rules with the same target pattern.  For example, numerous
rules make @samp{.o} files: one, from a @samp{.c} file with the C compiler;
another, from a @samp{.p} file with the Pascal compiler; and so on.  The rule
that actually applies is the one whose prerequisites exist or can be made.
So, if you have a file @file{foo.c}, @code{make} will run the C compiler;
otherwise, if you have a file @file{foo.p}, @code{make} will run the Pascal
compiler; and so on.

Of course, when you write the makefile, you know which implicit rule you
want @code{make} to use, and you know it will choose that one because you
know which possible prerequisite files are supposed to exist.
@xref{Catalogue of Rules, ,Catalogue of Implicit Rules},
for a catalogue of all the predefined implicit rules.

Above, we said an implicit rule applies if the required prerequisites ``exist
or can be made''.  A file ``can be made'' if it is mentioned explicitly in
the makefile as a target or a prerequisite, or if an implicit rule can be
recursively found for how to make it.  When an implicit prerequisite is the
result of another implicit rule, we say that @dfn{chaining} is occurring.
@xref{Chained Rules, ,Chains of Implicit Rules}.

In general, @code{make} searches for an implicit rule for each target, and
for each double-colon rule, that has no commands.  A file that is mentioned
only as a prerequisite is considered a target whose rule specifies nothing,
so implicit rule search happens for it.  @xref{Implicit Rule Search, ,Implicit Rule Search Algorithm}, for the
details of how the search is done.

Note that explicit prerequisites do not influence implicit rule search.
For example, consider this explicit rule:

@example
foo.o: foo.p
@end example

@noindent
The prerequisite on @file{foo.p} does not necessarily mean that
@code{make} will remake @file{foo.o} according to the implicit rule to
make an object file, a @file{.o} file, from a Pascal source file, a
@file{.p} file.  For example, if @file{foo.c} also exists, the implicit
rule to make an object file from a C source file is used instead,
because it appears before the Pascal rule in the list of predefined
implicit rules (@pxref{Catalogue of Rules, , Catalogue of Implicit
Rules}).

If you do not want an implicit rule to be used for a target that has no
commands, you can give that target empty commands by writing a semicolon
(@pxref{Empty Commands, ,Defining Empty Commands}).

@node Catalogue of Rules, Implicit Variables, Using Implicit, Implicit Rules
@section Catalogue of Implicit Rules
@cindex implicit rule, predefined
@cindex rule, implicit, predefined

Here is a catalogue of predefined implicit rules which are always
available unless the makefile explicitly overrides or cancels them.
@xref{Canceling Rules, ,Canceling Implicit Rules}, for information on
canceling or overriding an implicit rule.  The @samp{-r} or
@samp{--no-builtin-rules} option cancels all predefined rules.

Not all of these rules will always be defined, even when the @samp{-r}
option is not given.  Many of the predefined implicit rules are
implemented in @code{make} as suffix rules, so which ones will be
defined depends on the @dfn{suffix list} (the list of prerequisites of
the special target @code{.SUFFIXES}).  The default suffix list is:
@code{.out}, @code{.a}, @code{.ln}, @code{.o}, @code{.c}, @code{.cc},
@code{.C}, @code{.p}, @code{.f}, @code{.F}, @code{.r}, @code{.y},
@code{.l}, @code{.s}, @code{.S}, @code{.mod}, @code{.sym}, @code{.def},
@code{.h}, @code{.info}, @code{.dvi}, @code{.tex}, @code{.texinfo},
@code{.texi}, @code{.txinfo}, @code{.w}, @code{.ch} @code{.web},
@code{.sh}, @code{.elc}, @code{.el}.  All of the implicit rules
described below whose prerequisites have one of these suffixes are
actually suffix rules.  If you modify the suffix list, the only
predefined suffix rules in effect will be those named by one or two of
the suffixes that are on the list you specify; rules whose suffixes fail
to be on the list are disabled.  @xref{Suffix Rules, ,Old-Fashioned
Suffix Rules}, for full details on suffix rules.

@table @asis
@item Compiling C programs
@cindex C, rule to compile
@pindex cc
@pindex gcc
@pindex .o
@pindex .c
@file{@var{n}.o} is made automatically from @file{@var{n}.c} with
a command of the form @samp{$(CC) -c $(CPPFLAGS) $(CFLAGS)}.@refill

@item Compiling C++ programs
@cindex C++, rule to compile
@pindex g++
@pindex .C
@pindex .cc
@file{@var{n}.o} is made automatically from @file{@var{n}.cc} or
@file{@var{n}.C} with a command of the form @samp{$(CXX) -c $(CPPFLAGS)
$(CXXFLAGS)}.  We encourage you to use the suffix @samp{.cc} for C++
source files instead of @samp{.C}.@refill

@item Compiling Pascal programs
@cindex Pascal, rule to compile
@pindex pc
@pindex .p
@file{@var{n}.o} is made automatically from @file{@var{n}.p}
with the command @samp{$(PC) -c $(PFLAGS)}.@refill

@item Compiling Fortran and Ratfor programs
@cindex Fortran, rule to compile
@cindex Ratfor, rule to compile
@pindex f77
@pindex .f
@pindex .r
@pindex .F
@file{@var{n}.o} is made automatically from @file{@var{n}.r},
@file{@var{n}.F} or @file{@var{n}.f} by running the
Fortran compiler.  The precise command used is as follows:@refill

@table @samp
@item .f
@samp{$(FC) -c $(FFLAGS)}.
@item .F
@samp{$(FC) -c $(FFLAGS) $(CPPFLAGS)}.
@item .r
@samp{$(FC) -c $(FFLAGS) $(RFLAGS)}.
@end table

@item Preprocessing Fortran and Ratfor programs
@file{@var{n}.f} is made automatically from @file{@var{n}.r} or
@file{@var{n}.F}.  This rule runs just the preprocessor to convert a
Ratfor or preprocessable Fortran program into a strict Fortran
program.  The precise command used is as follows:@refill

@table @samp
@item .F
@samp{$(FC) -F $(CPPFLAGS) $(FFLAGS)}.
@item .r
@samp{$(FC) -F $(FFLAGS) $(RFLAGS)}.
@end table

@item Compiling Modula-2 programs
@cindex Modula-2, rule to compile
@pindex m2c
@pindex .sym
@pindex .def
@pindex .mod
@file{@var{n}.sym} is made from @file{@var{n}.def} with a command
of the form @samp{$(M2C) $(M2FLAGS) $(DEFFLAGS)}.  @file{@var{n}.o}
is made from @file{@var{n}.mod}; the form is:
@w{@samp{$(M2C) $(M2FLAGS) $(MODFLAGS)}}.@refill

@need 1200
@item Assembling and preprocessing assembler programs
@cindex assembly, rule to compile
@pindex as
@pindex .s
@file{@var{n}.o} is made automatically from @file{@var{n}.s} by
running the assembler, @code{as}.  The precise command is
@samp{$(AS) $(ASFLAGS)}.@refill

@pindex .S
@file{@var{n}.s} is made automatically from @file{@var{n}.S} by
running the C preprocessor, @code{cpp}.  The precise command is
@w{@samp{$(CPP) $(CPPFLAGS)}}.

@item Linking a single object file
@cindex linking, predefined rule for
@pindex ld
@pindex .o
@file{@var{n}} is made automatically from @file{@var{n}.o} by running
the linker (usually called @code{ld}) via the C compiler.  The precise
command used is @w{@samp{$(CC) $(LDFLAGS) @var{n}.o $(LOADLIBES) $(LDLIBS)}}.

This rule does the right thing for a simple program with only one
source file.  It will also do the right thing if there are multiple
object files (presumably coming from various other source files), one
of which has a name matching that of the executable file.  Thus,

@example
x: y.o z.o
@end example

@noindent
when @file{x.c}, @file{y.c} and @file{z.c} all exist will execute:

@example
@group
cc -c x.c -o x.o
cc -c y.c -o y.o
cc -c z.c -o z.o
cc x.o y.o z.o -o x
rm -f x.o
rm -f y.o
rm -f z.o
@end group
@end example

@noindent
In more complicated cases, such as when there is no object file whose
name derives from the executable file name, you must write an explicit
command for linking.

Each kind of file automatically made into @samp{.o} object files will
be automatically linked by using the compiler (@samp{$(CC)},
@samp{$(FC)} or @samp{$(PC)}; the C compiler @samp{$(CC)} is used to
assemble @samp{.s} files) without the @samp{-c} option.  This could be
done by using the @samp{.o} object files as intermediates, but it is
faster to do the compiling and linking in one step, so that's how it's
done.@refill

@item Yacc for C programs
@pindex yacc
@cindex Yacc, rule to run
@pindex .y
@file{@var{n}.c} is made automatically from @file{@var{n}.y} by
running Yacc with the command @samp{$(YACC) $(YFLAGS)}.

@item Lex for C programs
@pindex lex
@cindex Lex, rule to run
@pindex .l
@file{@var{n}.c} is made automatically from @file{@var{n}.l} by
by running Lex.  The actual command is @samp{$(LEX) $(LFLAGS)}.

@item Lex for Ratfor programs
@file{@var{n}.r} is made automatically from @file{@var{n}.l} by
by running Lex.  The actual command is @samp{$(LEX) $(LFLAGS)}.

The convention of using the same suffix @samp{.l} for all Lex files
regardless of whether they produce C code or Ratfor code makes it
impossible for @code{make} to determine automatically which of the two
languages you are using in any particular case.  If @code{make} is
called upon to remake an object file from a @samp{.l} file, it must
guess which compiler to use.  It will guess the C compiler, because
that is more common.  If you are using Ratfor, make sure @code{make}
knows this by mentioning @file{@var{n}.r} in the makefile.  Or, if you
are using Ratfor exclusively, with no C files, remove @samp{.c} from
the list of implicit rule suffixes with:@refill

@example
@group
.SUFFIXES:
.SUFFIXES: .o .r .f .l @dots{}
@end group
@end example

@item Making Lint Libraries from C, Yacc, or Lex programs
@pindex lint
@cindex @code{lint}, rule to run
@pindex .ln
@file{@var{n}.ln} is made from @file{@var{n}.c} by running @code{lint}.
The precise command is @w{@samp{$(LINT) $(LINTFLAGS) $(CPPFLAGS) -i}}.
The same command is used on the C code produced from
@file{@var{n}.y} or @file{@var{n}.l}.@refill

@item @TeX{} and Web
@cindex @TeX{}, rule to run
@cindex Web, rule to run
@pindex tex
@pindex cweave
@pindex weave
@pindex tangle
@pindex ctangle
@pindex .dvi
@pindex .tex
@pindex .web
@pindex .w
@pindex .ch
@file{@var{n}.dvi} is made from @file{@var{n}.tex} with the command
@samp{$(TEX)}.  @file{@var{n}.tex} is made from @file{@var{n}.web} with
@samp{$(WEAVE)}, or from @file{@var{n}.w} (and from @file{@var{n}.ch} if
it exists or can be made) with @samp{$(CWEAVE)}.  @file{@var{n}.p} is
made from @file{@var{n}.web} with @samp{$(TANGLE)} and @file{@var{n}.c}
is made from @file{@var{n}.w} (and from @file{@var{n}.ch} if it exists
or can be made) with @samp{$(CTANGLE)}.@refill

@item Texinfo and Info
@cindex Texinfo, rule to format
@cindex Info, rule to format
@pindex texi2dvi
@pindex makeinfo
@pindex .texinfo
@pindex .info
@pindex .texi
@pindex .txinfo
@file{@var{n}.dvi} is made from @file{@var{n}.texinfo},
@file{@var{n}.texi}, or @file{@var{n}.txinfo}, with the command
@w{@samp{$(TEXI2DVI) $(TEXI2DVI_FLAGS)}}.  @file{@var{n}.info} is made from
@file{@var{n}.texinfo}, @file{@var{n}.texi}, or @file{@var{n}.txinfo}, with
the command @w{@samp{$(MAKEINFO) $(MAKEINFO_FLAGS)}}.

@item RCS
@cindex RCS, rule to extract from
@pindex co
@pindex ,v @r{(RCS file extension)}
Any file @file{@var{n}} is extracted if necessary from an RCS file
named either @file{@var{n},v} or @file{RCS/@var{n},v}.  The precise
command used is @w{@samp{$(CO) $(COFLAGS)}}.  @file{@var{n}} will not be
extracted from RCS if it already exists, even if the RCS file is
newer.  The rules for RCS are terminal
(@pxref{Match-Anything Rules, ,Match-Anything Pattern Rules}),
so RCS files cannot be generated from another source; they must
actually exist.@refill

@item SCCS
@cindex SCCS, rule to extract from
@pindex get
@pindex s. @r{(SCCS file prefix)}
Any file @file{@var{n}} is extracted if necessary from an SCCS file
named either @file{s.@var{n}} or @file{SCCS/s.@var{n}}.  The precise
command used is @w{@samp{$(GET) $(GFLAGS)}}.  The rules for SCCS are
terminal (@pxref{Match-Anything Rules, ,Match-Anything Pattern Rules}),
so SCCS files cannot be generated from another source; they must
actually exist.@refill

@pindex .sh
For the benefit of SCCS, a file @file{@var{n}} is copied from
@file{@var{n}.sh} and made executable (by everyone).  This is for
shell scripts that are checked into SCCS.  Since RCS preserves the
execution permission of a file, you do not need to use this feature
with RCS.@refill

We recommend that you avoid using of SCCS.  RCS is widely held to be
superior, and is also free.  By choosing free software in place of
comparable (or inferior) proprietary software, you support the free
software movement.
@end table

Usually, you want to change only the variables listed in the table
above, which are documented in the following section.

However, the commands in built-in implicit rules actually use
variables such as @code{COMPILE.c}, @code{LINK.p}, and
@code{PREPROCESS.S}, whose values contain the commands listed above.

@code{make} follows the convention that the rule to compile a
@file{.@var{x}} source file uses the variable @code{COMPILE.@var{x}}.
Similarly, the rule to produce an executable from a @file{.@var{x}}
file uses @code{LINK.@var{x}}; and the rule to preprocess a
@file{.@var{x}} file uses @code{PREPROCESS.@var{x}}.

@vindex OUTPUT_OPTION
Every rule that produces an object file uses the variable
@code{OUTPUT_OPTION}.  @code{make} defines this variable either to
contain @samp{-o $@@}, or to be empty, depending on a compile-time
option.  You need the @samp{-o} option to ensure that the output goes
into the right file when the source file is in a different directory,
as when using @code{VPATH} (@pxref{Directory Search}).  However,
compilers on some systems do not accept a @samp{-o} switch for object
files.  If you use such a system, and use @code{VPATH}, some
compilations will put their output in the wrong place.
A possible workaround for this problem is to give @code{OUTPUT_OPTION}
the value @w{@samp{; mv $*.o $@@}}.

@node Implicit Variables, Chained Rules, Catalogue of Rules, Implicit Rules
@section Variables Used by Implicit Rules
@cindex flags for compilers

The commands in built-in implicit rules make liberal use of certain
predefined variables.  You can alter these variables in the makefile,
with arguments to @code{make}, or in the environment to alter how the
implicit rules work without redefining the rules themselves.  You can
cancel all variables used by implicit rules with the @samp{-R} or
@samp{--no-builtin-variables} option.

For example, the command used to compile a C source file actually says
@samp{$(CC) -c $(CFLAGS) $(CPPFLAGS)}.  The default values of the variables
used are @samp{cc} and nothing, resulting in the command @samp{cc -c}.  By
redefining @samp{CC} to @samp{ncc}, you could cause @samp{ncc} to be
used for all C compilations performed by the implicit rule.  By redefining
@samp{CFLAGS} to be @samp{-g}, you could pass the @samp{-g} option to
each compilation.  @emph{All} implicit rules that do C compilation use
@samp{$(CC)} to get the program name for the compiler and @emph{all}
include @samp{$(CFLAGS)} among the arguments given to the compiler.@refill

The variables used in implicit rules fall into two classes: those that are
names of programs (like @code{CC}) and those that contain arguments for the
programs (like @code{CFLAGS}).  (The ``name of a program'' may also contain
some command arguments, but it must start with an actual executable program
name.)  If a variable value contains more than one argument, separate them
with spaces.

Here is a table of variables used as names of programs in built-in rules:

@table @code
@item AR
@vindex AR
Archive-maintaining program; default @samp{ar}.
@pindex ar

@item AS
@vindex AS
Program for doing assembly; default @samp{as}.
@pindex as

@item CC
@vindex CC
Program for compiling C programs; default @samp{cc}.
@pindex cc

@item CXX
@vindex CXX
Program for compiling C++ programs; default @samp{g++}.
@pindex g++

@item CO
@vindex CO
Program for extracting a file from RCS; default @samp{co}.
@pindex co

@item CPP
@vindex CPP
Program for running the C preprocessor, with results to standard output;
default @samp{$(CC) -E}.

@item FC
@vindex FC
Program for compiling or preprocessing Fortran and Ratfor programs;
default @samp{f77}.
@pindex f77

@item GET
@vindex GET
Program for extracting a file from SCCS; default @samp{get}.
@pindex get

@item LEX
@vindex LEX
Program to use to turn Lex grammars into C programs or Ratfor programs;
default @samp{lex}.
@pindex lex

@item PC
@vindex PC
Program for compiling Pascal programs; default @samp{pc}.
@pindex pc

@item YACC
@vindex YACC
Program to use to turn Yacc grammars into C programs; default @samp{yacc}.
@pindex yacc

@item YACCR
@vindex YACCR
Program to use to turn Yacc grammars into Ratfor
programs; default @samp{yacc -r}.

@item MAKEINFO
@vindex MAKEINFO
Program to convert a Texinfo source file into an Info file; default
@samp{makeinfo}.
@pindex makeinfo

@item TEX
@vindex TEX
Program to make @TeX{} @sc{dvi} files from @TeX{} source;
default @samp{tex}.
@pindex tex

@item TEXI2DVI
@vindex TEXI2DVI
Program to make @TeX{} @sc{dvi} files from Texinfo source;
default @samp{texi2dvi}.
@pindex texi2dvi

@item WEAVE
@vindex WEAVE
Program to translate Web into @TeX{}; default @samp{weave}.
@pindex weave

@item CWEAVE
@vindex CWEAVE
Program to translate C Web into @TeX{}; default @samp{cweave}.
@pindex cweave

@item TANGLE
@vindex TANGLE
Program to translate Web into Pascal; default @samp{tangle}.
@pindex tangle

@item CTANGLE
@vindex CTANGLE
Program to translate C Web into C; default @samp{ctangle}.
@pindex ctangle

@item RM
@vindex RM
Command to remove a file; default @samp{rm -f}.
@pindex rm
@end table

Here is a table of variables whose values are additional arguments for the
programs above.  The default values for all of these is the empty
string, unless otherwise noted.

@table @code
@item ARFLAGS
@vindex ARFLAGS
Flags to give the archive-maintaining program; default @samp{rv}.

@item ASFLAGS
@vindex ASFLAGS
Extra flags to give to the assembler (when explicitly
invoked on a @samp{.s} or @samp{.S} file).

@item CFLAGS
@vindex CFLAGS
Extra flags to give to the C compiler.

@item CXXFLAGS
@vindex CXXFLAGS
Extra flags to give to the C++ compiler.

@item COFLAGS
@vindex COFLAGS
Extra flags to give to the RCS @code{co} program.

@item CPPFLAGS
@vindex CPPFLAGS
Extra flags to give to the C preprocessor and programs
that use it (the C and Fortran compilers).

@item FFLAGS
@vindex FFLAGS
Extra flags to give to the Fortran compiler.

@item GFLAGS
@vindex GFLAGS
Extra flags to give to the SCCS @code{get} program.

@item LDFLAGS
@vindex LDFLAGS
Extra flags to give to compilers when they are
supposed to invoke the linker, @samp{ld}.

@item LFLAGS
@vindex LFLAGS
Extra flags to give to Lex.

@item PFLAGS
@vindex PFLAGS
Extra flags to give to the Pascal compiler.

@item RFLAGS
@vindex RFLAGS
Extra flags to give to the Fortran compiler for Ratfor programs.

@item YFLAGS
@vindex YFLAGS
Extra flags to give to Yacc.
@end table

@node Chained Rules, Pattern Rules, Implicit Variables, Implicit Rules
@section Chains of Implicit Rules

@cindex chains of rules
@cindex rule, implicit, chains of
Sometimes a file can be made by a sequence of implicit rules.  For example,
a file @file{@var{n}.o} could be made from @file{@var{n}.y} by running
first Yacc and then @code{cc}.  Such a sequence is called a @dfn{chain}.

If the file @file{@var{n}.c} exists, or is mentioned in the makefile, no
special searching is required: @code{make} finds that the object file can
be made by C compilation from @file{@var{n}.c}; later on, when considering
how to make @file{@var{n}.c}, the rule for running Yacc is
used.  Ultimately both @file{@var{n}.c} and @file{@var{n}.o} are
updated.@refill

@cindex intermediate files
@cindex files, intermediate
However, even if @file{@var{n}.c} does not exist and is not mentioned,
@code{make} knows how to envision it as the missing link between
@file{@var{n}.o} and @file{@var{n}.y}!  In this case, @file{@var{n}.c} is
called an @dfn{intermediate file}.  Once @code{make} has decided to use the
intermediate file, it is entered in the data base as if it had been
mentioned in the makefile, along with the implicit rule that says how to
create it.@refill

Intermediate files are remade using their rules just like all other
files.  But intermediate files are treated differently in two ways.

The first difference is what happens if the intermediate file does not
exist.  If an ordinary file @var{b} does not exist, and @code{make}
considers a target that depends on @var{b}, it invariably creates
@var{b} and then updates the target from @var{b}.  But if @var{b} is an
intermediate file, then @code{make} can leave well enough alone.  It
won't bother updating @var{b}, or the ultimate target, unless some
prerequisite of @var{b} is newer than that target or there is some other
reason to update that target.

The second difference is that if @code{make} @emph{does} create @var{b}
in order to update something else, it deletes @var{b} later on after it
is no longer needed.  Therefore, an intermediate file which did not
exist before @code{make} also does not exist after @code{make}.
@code{make} reports the deletion to you by printing a @samp{rm -f}
command showing which file it is deleting.

Ordinarily, a file cannot be intermediate if it is mentioned in the
makefile as a target or prerequisite.  However, you can explicitly mark a
file as intermediate by listing it as a prerequisite of the special target
@code{.INTERMEDIATE}.  This takes effect even if the file is mentioned
explicitly in some other way.

@cindex intermediate files, preserving
@cindex preserving intermediate files
@cindex secondary files
You can prevent automatic deletion of an intermediate file by marking it
as a @dfn{secondary} file.  To do this, list it as a prerequisite of the
special target @code{.SECONDARY}.  When a file is secondary, @code{make}
will not create the file merely because it does not already exist, but
@code{make} does not automatically delete the file.  Marking a file as
secondary also marks it as intermediate.

You can list the target pattern of an implicit rule (such as @samp{%.o})
as a prerequisite of the special target @code{.PRECIOUS} to preserve
intermediate files made by implicit rules whose target patterns match
that file's name; see @ref{Interrupts}.@refill
@cindex preserving with @code{.PRECIOUS}
@cindex @code{.PRECIOUS} intermediate files

A chain can involve more than two implicit rules.  For example, it is
possible to make a file @file{foo} from @file{RCS/foo.y,v} by running RCS,
Yacc and @code{cc}.  Then both @file{foo.y} and @file{foo.c} are
intermediate files that are deleted at the end.@refill

No single implicit rule can appear more than once in a chain.  This means
that @code{make} will not even consider such a ridiculous thing as making
@file{foo} from @file{foo.o.o} by running the linker twice.  This
constraint has the added benefit of preventing any infinite loop in the
search for an implicit rule chain.

There are some special implicit rules to optimize certain cases that would
otherwise be handled by rule chains.  For example, making @file{foo} from
@file{foo.c} could be handled by compiling and linking with separate
chained rules, using @file{foo.o} as an intermediate file.  But what
actually happens is that a special rule for this case does the compilation
and linking with a single @code{cc} command.  The optimized rule is used in
preference to the step-by-step chain because it comes earlier in the
ordering of rules.

@node Pattern Rules, Last Resort, Chained Rules, Implicit Rules
@section Defining and Redefining Pattern Rules

You define an implicit rule by writing a @dfn{pattern rule}.  A pattern
rule looks like an ordinary rule, except that its target contains the
character @samp{%} (exactly one of them).  The target is considered a
pattern for matching file names; the @samp{%} can match any nonempty
substring, while other characters match only themselves.  The prerequisites
likewise use @samp{%} to show how their names relate to the target name.

Thus, a pattern rule @samp{%.o : %.c} says how to make any file
@file{@var{stem}.o} from another file @file{@var{stem}.c}.@refill

Note that expansion using @samp{%} in pattern rules occurs
@strong{after} any variable or function expansions, which take place
when the makefile is read.  @xref{Using Variables, , How to Use
Variables}, and @ref{Functions, ,Functions for Transforming Text}.

@menu
* Pattern Intro::               An introduction to pattern rules.
* Pattern Examples::            Examples of pattern rules.
* Automatic::                   How to use automatic variables in the
                                  commands of implicit rules.
* Pattern Match::               How patterns match.
* Match-Anything Rules::        Precautions you should take prior to
                                  defining rules that can match any
                                  target file whatever.
* Canceling Rules::             How to override or cancel built-in rules.
@end menu

@node Pattern Intro, Pattern Examples,  , Pattern Rules
@subsection Introduction to Pattern Rules
@cindex pattern rule
@cindex rule, pattern

A pattern rule contains the character @samp{%} (exactly one of them)
in the target; otherwise, it looks exactly like an ordinary rule.  The
target is a pattern for matching file names; the @samp{%} matches any
nonempty substring, while other characters match only themselves.
@cindex target pattern, implicit
@cindex @code{%}, in pattern rules

For example, @samp{%.c} as a pattern matches any file name that ends in
@samp{.c}.  @samp{s.%.c} as a pattern matches any file name that starts
with @samp{s.}, ends in @samp{.c} and is at least five characters long.
(There must be at least one character to match the @samp{%}.)  The substring
that the @samp{%} matches is called the @dfn{stem}.@refill

@samp{%} in a prerequisite of a pattern rule stands for the same stem
that was matched by the @samp{%} in the target.  In order for
the pattern rule to apply, its target pattern must match the file name
under consideration, and its prerequisite patterns must name files that
exist or can be made.  These files become prerequisites of the target.
@cindex prerequisite pattern, implicit

Thus, a rule of the form

@example
%.o : %.c ; @var{command}@dots{}
@end example

@noindent
specifies how to make a file @file{@var{n}.o}, with another file
@file{@var{n}.c} as its prerequisite, provided that @file{@var{n}.c}
exists or can be made.

There may also be prerequisites that do not use @samp{%}; such a prerequisite
attaches to every file made by this pattern rule.  These unvarying
prerequisites are useful occasionally.

A pattern rule need not have any prerequisites that contain @samp{%}, or
in fact any prerequisites at all.  Such a rule is effectively a general
wildcard.  It provides a way to make any file that matches the target
pattern.  @xref{Last Resort}.

@c !!! The end of of this paragraph should be rewritten.  --bob
Pattern rules may have more than one target.  Unlike normal rules, this
does not act as many different rules with the same prerequisites and
commands.  If a pattern rule has multiple targets, @code{make} knows that
the rule's commands are responsible for making all of the targets.  The
commands are executed only once to make all the targets.  When searching
for a pattern rule to match a target, the target patterns of a rule other
than the one that matches the target in need of a rule are incidental:
@code{make} worries only about giving commands and prerequisites to the file
presently in question.  However, when this file's commands are run, the
other targets are marked as having been updated themselves.
@cindex multiple targets, in pattern rule
@cindex target, multiple in pattern rule

The order in which pattern rules appear in the makefile is important
since this is the order in which they are considered.
Of equally applicable
rules, only the first one found is used.  The rules you write take precedence
over those that are built in.  Note however, that a rule whose
prerequisites actually exist or are mentioned always takes priority over a
rule with prerequisites that must be made by chaining other implicit rules.
@cindex pattern rules, order of
@cindex order of pattern rules

@node Pattern Examples, Automatic, Pattern Intro, Pattern Rules
@subsection Pattern Rule Examples

Here are some examples of pattern rules actually predefined in
@code{make}.  First, the rule that compiles @samp{.c} files into @samp{.o}
files:@refill

@example
%.o : %.c
        $(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@@
@end example

@noindent
defines a rule that can make any file @file{@var{x}.o} from
@file{@var{x}.c}.  The command uses the automatic variables @samp{$@@} and
@samp{$<} to substitute the names of the target file and the source file
in each case where the rule applies (@pxref{Automatic, ,Automatic Variables}).@refill

Here is a second built-in rule:

@example
% :: RCS/%,v
        $(CO) $(COFLAGS) $<
@end example

@noindent
defines a rule that can make any file @file{@var{x}} whatsoever from a
corresponding file @file{@var{x},v} in the subdirectory @file{RCS}.  Since
the target is @samp{%}, this rule will apply to any file whatever, provided
the appropriate prerequisite file exists.  The double colon makes the rule
@dfn{terminal}, which means that its prerequisite may not be an intermediate
file (@pxref{Match-Anything Rules, ,Match-Anything Pattern Rules}).@refill

@need 500
This pattern rule has two targets:

@example
@group
%.tab.c %.tab.h: %.y
        bison -d $<
@end group
@end example

@noindent
@c The following paragraph is rewritten to avoid overfull hboxes
This tells @code{make} that the command @samp{bison -d @var{x}.y} will
make both @file{@var{x}.tab.c} and @file{@var{x}.tab.h}.  If the file
@file{foo} depends on the files @file{parse.tab.o} and @file{scan.o}
and the file @file{scan.o} depends on the file @file{parse.tab.h},
when @file{parse.y} is changed, the command @samp{bison -d parse.y}
will be executed only once, and the prerequisites of both
@file{parse.tab.o} and @file{scan.o} will be satisfied.  (Presumably
the file @file{parse.tab.o} will be recompiled from @file{parse.tab.c}
and the file @file{scan.o} from @file{scan.c}, while @file{foo} is
linked from @file{parse.tab.o}, @file{scan.o}, and its other
prerequisites, and it will execute happily ever after.)@refill

@node Automatic, Pattern Match, Pattern Examples, Pattern Rules
@subsection Automatic Variables
@cindex automatic variables
@cindex variables, automatic
@cindex variables, and implicit rule

Suppose you are writing a pattern rule to compile a @samp{.c} file into a
@samp{.o} file: how do you write the @samp{cc} command so that it operates
on the right source file name?  You cannot write the name in the command,
because the name is different each time the implicit rule is applied.

What you do is use a special feature of @code{make}, the @dfn{automatic
variables}.  These variables have values computed afresh for each rule that
is executed, based on the target and prerequisites of the rule.  In this
example, you would use @samp{$@@} for the object file name and @samp{$<}
for the source file name.

Here is a table of automatic variables:

@table @code
@vindex $@@
@vindex @@ @r{(automatic variable)}
@item $@@
The file name of the target of the rule.  If the target is an archive
member, then @samp{$@@} is the name of the archive file.  In a pattern
rule that has multiple targets (@pxref{Pattern Intro, ,Introduction to
Pattern Rules}), @samp{$@@} is the name of whichever target caused the
rule's commands to be run.

@vindex $%
@vindex % @r{(automatic variable)}
@item $%
The target member name, when the target is an archive member.
@xref{Archives}.  For example, if the target is @file{foo.a(bar.o)} then
@samp{$%} is @file{bar.o} and @samp{$@@} is @file{foo.a}.  @samp{$%} is
empty when the target is not an archive member.

@vindex $<
@vindex < @r{(automatic variable)}
@item $<
The name of the first prerequisite.  If the target got its commands from
an implicit rule, this will be the first prerequisite added by the
implicit rule (@pxref{Implicit Rules}).

@vindex $?
@vindex ? @r{(automatic variable)}
@item $?
The names of all the prerequisites that are newer than the target, with
spaces between them.  For prerequisites which are archive members, only
the member named is used (@pxref{Archives}).
@cindex prerequisites, list of changed
@cindex list of changed prerequisites

@vindex $^
@vindex ^ @r{(automatic variable)}
@item $^
The names of all the prerequisites, with spaces between them.  For
prerequisites which are archive members, only the member named is used
(@pxref{Archives}).  A target has only one prerequisite on each other file
it depends on, no matter how many times each file is listed as a
prerequisite.  So if you list a prerequisite more than once for a target,
the value of @code{$^} contains just one copy of the name.
@cindex prerequisites, list of all
@cindex list of all prerequisites

@vindex $+
@vindex + @r{(automatic variable)}
@item $+
This is like @samp{$^}, but prerequisites listed more than once are
duplicated in the order they were listed in the makefile.  This is
primarily useful for use in linking commands where it is meaningful to
repeat library file names in a particular order.

@vindex $*
@vindex * @r{(automatic variable)}
@item $*
The stem with which an implicit rule matches (@pxref{Pattern Match, ,How
Patterns Match}).  If the target is @file{dir/a.foo.b} and the target
pattern is @file{a.%.b} then the stem is @file{dir/foo}.  The stem is
useful for constructing names of related files.@refill
@cindex stem, variable for

In a static pattern rule, the stem is part of the file name that matched
the @samp{%} in the target pattern.

In an explicit rule, there is no stem; so @samp{$*} cannot be determined
in that way.  Instead, if the target name ends with a recognized suffix
(@pxref{Suffix Rules, ,Old-Fashioned Suffix Rules}), @samp{$*} is set to
the target name minus the suffix.  For example, if the target name is
@samp{foo.c}, then @samp{$*} is set to @samp{foo}, since @samp{.c} is a
suffix.  GNU @code{make} does this bizarre thing only for compatibility
with other implementations of @code{make}.  You should generally avoid
using @samp{$*} except in implicit rules or static pattern rules.@refill

If the target name in an explicit rule does not end with a recognized
suffix, @samp{$*} is set to the empty string for that rule.
@end table

@samp{$?} is useful even in explicit rules when you wish to operate on only
the prerequisites that have changed.  For example, suppose that an archive
named @file{lib} is supposed to contain copies of several object files.
This rule copies just the changed object files into the archive:

@example
@group
lib: foo.o bar.o lose.o win.o
        ar r lib $?
@end group
@end example

Of the variables listed above, four have values that are single file
names, and three have values that are lists of file names.  These seven
have variants that get just the file's directory name or just the file
name within the directory.  The variant variables' names are formed by
appending @samp{D} or @samp{F}, respectively.  These variants are
semi-obsolete in GNU @code{make} since the functions @code{dir} and
@code{notdir} can be used to get a similar effect (@pxref{File Name
Functions, , Functions for File Names}).  Note, however, that the
@samp{F} variants all omit the trailing slash which always appears in
the output of the @code{dir} function.  Here is a table of the variants:

@table @samp
@vindex $(@@D)
@vindex @@D @r{(automatic variable)}
@item $(@@D)
The directory part of the file name of the target, with the trailing
slash removed.  If the value of @samp{$@@} is @file{dir/foo.o} then
@samp{$(@@D)} is @file{dir}.  This value is @file{.} if @samp{$@@} does
not contain a slash.

@vindex $(@@F)
@vindex @@F @r{(automatic variable)}
@item $(@@F)
The file-within-directory part of the file name of the target.  If the
value of @samp{$@@} is @file{dir/foo.o} then @samp{$(@@F)} is
@file{foo.o}.  @samp{$(@@F)} is equivalent to @samp{$(notdir $@@)}.

@vindex $(*D)
@vindex *D @r{(automatic variable)}
@item $(*D)
@vindex $(*F)
@vindex *F @r{(automatic variable)}
@itemx $(*F)
The directory part and the file-within-directory
part of the stem; @file{dir} and @file{foo} in this example.

@vindex $(%D)
@vindex %D @r{(automatic variable)}
@item $(%D)
@vindex $(%F)
@vindex %F @r{(automatic variable)}
@itemx $(%F)
The directory part and the file-within-directory part of the target
archive member name.  This makes sense only for archive member targets
of the form @file{@var{archive}(@var{member})} and is useful only when
@var{member} may contain a directory name.  (@xref{Archive Members,
,Archive Members as Targets}.)

@vindex $(<D)
@vindex <D @r{(automatic variable)}
@item $(<D)
@vindex $(<F)
@vindex <F @r{(automatic variable)}
@itemx $(<F)
The directory part and the file-within-directory
part of the first prerequisite.

@vindex $(^D)
@vindex ^D @r{(automatic variable)}
@item $(^D)
@vindex $(^F)
@vindex ^F @r{(automatic variable)}
@itemx $(^F)
Lists of the directory parts and the file-within-directory
parts of all prerequisites.

@vindex $(?D)
@vindex ?D @r{(automatic variable)}
@item $(?D)
@vindex $(?F)
@vindex ?F @r{(automatic variable)}
@itemx $(?F)
Lists of the directory parts and the file-within-directory parts of
all prerequisites that are newer than the target.
@end table

Note that we use a special stylistic convention when we talk about these
automatic variables; we write ``the value of @samp{$<}'', rather than
@w{``the variable @code{<}''} as we would write for ordinary variables
such as @code{objects} and @code{CFLAGS}.  We think this convention
looks more natural in this special case.  Please do not assume it has a
deep significance; @samp{$<} refers to the variable named @code{<} just
as @samp{$(CFLAGS)} refers to the variable named @code{CFLAGS}.
You could just as well use @samp{$(<)} in place of @samp{$<}.

@node Pattern Match, Match-Anything Rules, Automatic, Pattern Rules
@subsection How Patterns Match

@cindex stem
A target pattern is composed of a @samp{%} between a prefix and a suffix,
either or both of which may be empty.  The pattern matches a file name only
if the file name starts with the prefix and ends with the suffix, without
overlap.  The text between the prefix and the suffix is called the
@dfn{stem}.  Thus, when the pattern @samp{%.o} matches the file name
@file{test.o}, the stem is @samp{test}.  The pattern rule prerequisites are
turned into actual file names by substituting the stem for the character
@samp{%}.  Thus, if in the same example one of the prerequisites is written
as @samp{%.c}, it expands to @samp{test.c}.@refill

When the target pattern does not contain a slash (and it usually does
not), directory names in the file names are removed from the file name
before it is compared with the target prefix and suffix.  After the
comparison of the file name to the target pattern, the directory
names, along with the slash that ends them, are added on to the
prerequisite file names generated from the pattern rule's prerequisite
patterns and the file name. The directories are ignored only for the
purpose of finding an implicit rule to use, not in the application of
that rule.  Thus, @samp{e%t} matches the file name @file{src/eat},
with @samp{src/a} as the stem.  When prerequisites are turned into file
names, the directories from the stem are added at the front, while the
rest of the stem is substituted for the @samp{%}.  The stem
@samp{src/a} with a prerequisite pattern @samp{c%r} gives the file name
@file{src/car}.@refill

@node Match-Anything Rules, Canceling Rules, Pattern Match, Pattern Rules
@subsection Match-Anything Pattern Rules

@cindex match-anything rule
@cindex terminal rule
When a pattern rule's target is just @samp{%}, it matches any file name
whatever.  We call these rules @dfn{match-anything} rules.  They are very
useful, but it can take a lot of time for @code{make} to think about them,
because it must consider every such rule for each file name listed either
as a target or as a prerequisite.

Suppose the makefile mentions @file{foo.c}.  For this target, @code{make}
would have to consider making it by linking an object file @file{foo.c.o},
or by C compilation-and-linking in one step from @file{foo.c.c}, or by
Pascal compilation-and-linking from @file{foo.c.p}, and many other
possibilities.

We know these possibilities are ridiculous since @file{foo.c} is a C source
file, not an executable.  If @code{make} did consider these possibilities,
it would ultimately reject them, because files such as @file{foo.c.o} and
@file{foo.c.p} would not exist.  But these possibilities are so
numerous that @code{make} would run very slowly if it had to consider
them.@refill

To gain speed, we have put various constraints on the way @code{make}
considers match-anything rules.  There are two different constraints that
can be applied, and each time you define a match-anything rule you must
choose one or the other for that rule.

One choice is to mark the match-anything rule as @dfn{terminal} by defining
it with a double colon.  When a rule is terminal, it does not apply unless
its prerequisites actually exist.  Prerequisites that could be made with
other implicit rules are not good enough.  In other words, no further
chaining is allowed beyond a terminal rule.

For example, the built-in implicit rules for extracting sources from RCS
and SCCS files are terminal; as a result, if the file @file{foo.c,v} does
not exist, @code{make} will not even consider trying to make it as an
intermediate file from @file{foo.c,v.o} or from @file{RCS/SCCS/s.foo.c,v}.
RCS and SCCS files are generally ultimate source files, which should not be
remade from any other files; therefore, @code{make} can save time by not
looking for ways to remake them.@refill

If you do not mark the match-anything rule as terminal, then it is
nonterminal.  A nonterminal match-anything rule cannot apply to a file name
that indicates a specific type of data.  A file name indicates a specific
type of data if some non-match-anything implicit rule target matches it.

For example, the file name @file{foo.c} matches the target for the pattern
rule @samp{%.c : %.y} (the rule to run Yacc).  Regardless of whether this
rule is actually applicable (which happens only if there is a file
@file{foo.y}), the fact that its target matches is enough to prevent
consideration of any nonterminal match-anything rules for the file
@file{foo.c}.  Thus, @code{make} will not even consider trying to make
@file{foo.c} as an executable file from @file{foo.c.o}, @file{foo.c.c},
@file{foo.c.p}, etc.@refill

The motivation for this constraint is that nonterminal match-anything
rules are used for making files containing specific types of data (such as
executable files) and a file name with a recognized suffix indicates some
other specific type of data (such as a C source file).

Special built-in dummy pattern rules are provided solely to recognize
certain file names so that nonterminal match-anything rules will not be
considered.  These dummy rules have no prerequisites and no commands, and
they are ignored for all other purposes.  For example, the built-in
implicit rule

@example
%.p :
@end example

@noindent
exists to make sure that Pascal source files such as @file{foo.p} match a
specific target pattern and thereby prevent time from being wasted looking
for @file{foo.p.o} or @file{foo.p.c}.

Dummy pattern rules such as the one for @samp{%.p} are made for every
suffix listed as valid for use in suffix rules (@pxref{Suffix Rules, ,Old-Fashioned Suffix Rules}).

@node Canceling Rules,  , Match-Anything Rules, Pattern Rules
@subsection Canceling Implicit Rules

You can override a built-in implicit rule (or one you have defined
yourself) by defining a new pattern rule with the same target and
prerequisites, but different commands.  When the new rule is defined, the
built-in one is replaced.  The new rule's position in the sequence of
implicit rules is determined by where you write the new rule.

You can cancel a built-in implicit rule by defining a pattern rule with the
same target and prerequisites, but no commands.  For example, the following
would cancel the rule that runs the assembler:

@example
%.o : %.s
@end example

@node Last Resort, Suffix Rules, Pattern Rules, Implicit Rules
@section Defining Last-Resort Default Rules
@cindex last-resort default rules
@cindex default rules, last-resort

You can define a last-resort implicit rule by writing a terminal
match-anything pattern rule with no prerequisites (@pxref{Match-Anything
Rules}).  This is just like any other pattern rule; the only thing
special about it is that it will match any target.  So such a rule's
commands are used for all targets and prerequisites that have no commands
of their own and for which no other implicit rule applies.

For example, when testing a makefile, you might not care if the source
files contain real data, only that they exist.  Then you might do this:

@example
%::
        touch $@@
@end example

@noindent
to cause all the source files needed (as prerequisites) to be created
automatically.

@findex .DEFAULT
You can instead define commands to be used for targets for which there
are no rules at all, even ones which don't specify commands.  You do
this by writing a rule for the target @code{.DEFAULT}.  Such a rule's
commands are used for all prerequisites which do not appear as targets in
any explicit rule, and for which no implicit rule applies.  Naturally,
there is no @code{.DEFAULT} rule unless you write one.

If you use @code{.DEFAULT} with no commands or prerequisites:

@example
.DEFAULT:
@end example

@noindent
the commands previously stored for @code{.DEFAULT} are cleared.
Then @code{make} acts as if you had never defined @code{.DEFAULT} at all.

If you do not want a target to get the commands from a match-anything
pattern rule or @code{.DEFAULT}, but you also do not want any commands
to be run for the target, you can give it empty commands (@pxref{Empty
Commands, ,Defining Empty Commands}).@refill

You can use a last-resort rule to override part of another makefile.
@xref{Overriding Makefiles, , Overriding Part of Another Makefile}.

@node Suffix Rules, Implicit Rule Search, Last Resort, Implicit Rules
@section Old-Fashioned Suffix Rules
@cindex old-fashioned suffix rules
@cindex suffix rule

@dfn{Suffix rules} are the old-fashioned way of defining implicit rules for
@code{make}.  Suffix rules are obsolete because pattern rules are more
general and clearer.  They are supported in GNU @code{make} for
compatibility with old makefiles.  They come in two kinds:
@dfn{double-suffix} and @dfn{single-suffix}.@refill

A double-suffix rule is defined by a pair of suffixes: the target suffix
and the source suffix.  It matches any file whose name ends with the
target suffix.  The corresponding implicit prerequisite is made by
replacing the target suffix with the source suffix in the file name.  A
two-suffix rule whose target and source suffixes are @samp{.o} and
@samp{.c} is equivalent to the pattern rule @samp{%.o : %.c}.

A single-suffix rule is defined by a single suffix, which is the source
suffix.  It matches any file name, and the corresponding implicit
prerequisite name is made by appending the source suffix.  A single-suffix
rule whose source suffix is @samp{.c} is equivalent to the pattern rule
@samp{% : %.c}.

Suffix rule definitions are recognized by comparing each rule's target
against a defined list of known suffixes.  When @code{make} sees a rule
whose target is a known suffix, this rule is considered a single-suffix
rule.  When @code{make} sees a rule whose target is two known suffixes
concatenated, this rule is taken as a double-suffix rule.

For example, @samp{.c} and @samp{.o} are both on the default list of
known suffixes.  Therefore, if you define a rule whose target is
@samp{.c.o}, @code{make} takes it to be a double-suffix rule with source
suffix @samp{.c} and target suffix @samp{.o}.  Here is the old-fashioned
way to define the rule for compiling a C source file:@refill

@example
.c.o:
        $(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@@ $<
@end example

Suffix rules cannot have any prerequisites of their own.  If they have any,
they are treated as normal files with funny names, not as suffix rules.
Thus, the rule:

@example
.c.o: foo.h
        $(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@@ $<
@end example

@noindent
tells how to make the file @file{.c.o} from the prerequisite file
@file{foo.h}, and is not at all like the pattern rule:

@example
%.o: %.c foo.h
        $(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@@ $<
@end example

@noindent
which tells how to make @samp{.o} files from @samp{.c} files, and makes all
@samp{.o} files using this pattern rule also depend on @file{foo.h}.

Suffix rules with no commands are also meaningless.  They do not remove
previous rules as do pattern rules with no commands (@pxref{Canceling
Rules, , Canceling Implicit Rules}).  They simply enter the suffix or pair of suffixes concatenated as
a target in the data base.@refill

@findex .SUFFIXES
The known suffixes are simply the names of the prerequisites of the special
target @code{.SUFFIXES}.  You can add your own suffixes by writing a rule
for @code{.SUFFIXES} that adds more prerequisites, as in:

@example
.SUFFIXES: .hack .win
@end example

@noindent
which adds @samp{.hack} and @samp{.win} to the end of the list of suffixes.

If you wish to eliminate the default known suffixes instead of just adding
to them, write a rule for @code{.SUFFIXES} with no prerequisites.  By
special dispensation, this eliminates all existing prerequisites of
@code{.SUFFIXES}.  You can then write another rule to add the suffixes you
want.  For example,

@example
@group
.SUFFIXES:            # @r{Delete the default suffixes}
.SUFFIXES: .c .o .h   # @r{Define our suffix list}
@end group
@end example

The @samp{-r} or @samp{--no-builtin-rules} flag causes the default
list of suffixes to be empty.

@vindex SUFFIXES
The variable @code{SUFFIXES} is defined to the default list of suffixes
before @code{make} reads any makefiles.  You can change the list of suffixes
with a rule for the special target @code{.SUFFIXES}, but that does not alter
this variable.

@node Implicit Rule Search,  , Suffix Rules, Implicit Rules
@section Implicit Rule Search Algorithm
@cindex implicit rule, search algorithm
@cindex search algorithm, implicit rule

Here is the procedure @code{make} uses for searching for an implicit rule
for a target @var{t}.  This procedure is followed for each double-colon
rule with no commands, for each target of ordinary rules none of which have
commands, and for each prerequisite that is not the target of any rule.  It
is also followed recursively for prerequisites that come from implicit
rules, in the search for a chain of rules.

Suffix rules are not mentioned in this algorithm because suffix rules are
converted to equivalent pattern rules once the makefiles have been read in.

For an archive member target of the form
@samp{@var{archive}(@var{member})}, the following algorithm is run
twice, first using the entire target name @var{t}, and second using
@samp{(@var{member})} as the target @var{t} if the first run found no
rule.@refill

@enumerate
@item
Split @var{t} into a directory part, called @var{d}, and the rest,
called @var{n}.  For example, if @var{t} is @samp{src/foo.o}, then
@var{d} is @samp{src/} and @var{n} is @samp{foo.o}.@refill

@item
Make a list of all the pattern rules one of whose targets matches
@var{t} or @var{n}.  If the target pattern contains a slash, it is
matched against @var{t}; otherwise, against @var{n}.

@item
If any rule in that list is @emph{not} a match-anything rule, then
remove all nonterminal match-anything rules from the list.

@item
Remove from the list all rules with no commands.

@item
For each pattern rule in the list:

@enumerate a
@item
Find the stem @var{s}, which is the nonempty part of @var{t} or @var{n}
matched by the @samp{%} in the target pattern.@refill

@item
Compute the prerequisite names by substituting @var{s} for @samp{%}; if
the target pattern does not contain a slash, append @var{d} to
the front of each prerequisite name.@refill

@item
Test whether all the prerequisites exist or ought to exist.  (If a
file name is mentioned in the makefile as a target or as an explicit
prerequisite, then we say it ought to exist.)

If all prerequisites exist or ought to exist, or there are no prerequisites,
then this rule applies.
@end enumerate

@item
If no pattern rule has been found so far, try harder.
For each pattern rule in the list:

@enumerate a
@item
If the rule is terminal, ignore it and go on to the next rule.

@item
Compute the prerequisite names as before.

@item
Test whether all the prerequisites exist or ought to exist.

@item
For each prerequisite that does not exist, follow this algorithm
recursively to see if the prerequisite can be made by an implicit
rule.

@item
If all prerequisites exist, ought to exist, or can be
made by implicit rules, then this rule applies.
@end enumerate

@item
If no implicit rule applies, the rule for @code{.DEFAULT}, if any,
applies.  In that case, give @var{t} the same commands that
@code{.DEFAULT} has.  Otherwise, there are no commands for @var{t}.
@end enumerate

Once a rule that applies has been found, for each target pattern of the
rule other than the one that matched @var{t} or @var{n}, the @samp{%} in
the pattern is replaced with @var{s} and the resultant file name is stored
until the commands to remake the target file @var{t} are executed.  After
these commands are executed, each of these stored file names are entered
into the data base and marked as having been updated and having the same
update status as the file @var{t}.

When the commands of a pattern rule are executed for @var{t}, the automatic
variables are set corresponding to the target and prerequisites.
@xref{Automatic, ,Automatic Variables}.

@node Archives, Features, Implicit Rules, Top
@chapter Using @code{make} to Update Archive Files
@cindex archive

@dfn{Archive files} are files containing named subfiles called
@dfn{members}; they are maintained with the program @code{ar} and their
main use is as subroutine libraries for linking.

@menu
* Archive Members::             Archive members as targets.
* Archive Update::              The implicit rule for archive member targets.
* Archive Pitfalls::            Dangers to watch out for when using archives.
* Archive Suffix Rules::        You can write a special kind of suffix rule
                                  for updating archives.
@end menu

@node Archive Members, Archive Update,  , Archives
@section Archive Members as Targets
@cindex archive member targets

An individual member of an archive file can be used as a target or
prerequisite in @code{make}.  You specify the member named @var{member} in
archive file @var{archive} as follows:

@example
@var{archive}(@var{member})
@end example

@noindent
This construct is available only in targets and prerequisites, not in
commands!  Most programs that you might use in commands do not support this
syntax and cannot act directly on archive members.  Only @code{ar} and
other programs specifically designed to operate on archives can do so.
Therefore, valid commands to update an archive member target probably must
use @code{ar}.  For example, this rule says to create a member
@file{hack.o} in archive @file{foolib} by copying the file @file{hack.o}:

@example
foolib(hack.o) : hack.o
        ar cr foolib hack.o
@end example

In fact, nearly all archive member targets are updated in just this way
and there is an implicit rule to do it for you.  @strong{Note:} The
@samp{c} flag to @code{ar} is required if the archive file does not
already exist.

To specify several members in the same archive, you can write all the
member names together between the parentheses.  For example:

@example
foolib(hack.o kludge.o)
@end example

@noindent
is equivalent to:

@example
foolib(hack.o) foolib(kludge.o)
@end example

@cindex wildcard, in archive member
You can also use shell-style wildcards in an archive member reference.
@xref{Wildcards, ,Using Wildcard Characters in File Names}.  For
example, @w{@samp{foolib(*.o)}} expands to all existing members of the
@file{foolib} archive whose names end in @samp{.o}; perhaps
@samp{@w{foolib(hack.o)} @w{foolib(kludge.o)}}.

@node Archive Update
@section Implicit Rule for Archive Member Targets

Recall that a target that looks like @file{@var{a}(@var{m})} stands for the
member named @var{m} in the archive file @var{a}.

When @code{make} looks for an implicit rule for such a target, as a special
feature it considers implicit rules that match @file{(@var{m})}, as well as
those that match the actual target @file{@var{a}(@var{m})}.

This causes one special rule whose target is @file{(%)} to match.  This
rule updates the target @file{@var{a}(@var{m})} by copying the file @var{m}
into the archive.  For example, it will update the archive member target
@file{foo.a(bar.o)} by copying the @emph{file} @file{bar.o} into the
archive @file{foo.a} as a @emph{member} named @file{bar.o}.

When this rule is chained with others, the result is very powerful.
Thus, @samp{make "foo.a(bar.o)"} (the quotes are needed to protect the
@samp{(} and @samp{)} from being interpreted specially by the shell) in
the presence of a file @file{bar.c} is enough to cause the following
commands to be run, even without a makefile:

@example
cc -c bar.c -o bar.o
ar r foo.a bar.o
rm -f bar.o
@end example

@noindent
Here @code{make} has envisioned the file @file{bar.o} as an intermediate
file.  @xref{Chained Rules, ,Chains of Implicit Rules}.

Implicit rules such as this one are written using the automatic variable
@samp{$%}.  @xref{Automatic, ,Automatic Variables}.

An archive member name in an archive cannot contain a directory name, but
it may be useful in a makefile to pretend that it does.  If you write an
archive member target @file{foo.a(dir/file.o)}, @code{make} will perform
automatic updating with this command:

@example
ar r foo.a dir/file.o
@end example

@noindent
which has the effect of copying the file @file{dir/file.o} into a member
named @file{file.o}.  In connection with such usage, the automatic variables
@code{%D} and @code{%F} may be useful.

@menu
* Archive Symbols::             How to update archive symbol directories.
@end menu

@node Archive Symbols,  ,  , Archive Update
@subsection Updating Archive Symbol Directories
@cindex @code{__.SYMDEF}
@cindex updating archive symbol directories
@cindex archive symbol directory updating
@cindex symbol directories, updating archive
@cindex directories, updating archive symbol

An archive file that is used as a library usually contains a special member
named @file{__.SYMDEF} that contains a directory of the external symbol
names defined by all the other members.  After you update any other
members, you need to update @file{__.SYMDEF} so that it will summarize the
other members properly.  This is done by running the @code{ranlib} program:

@example
ranlib @var{archivefile}
@end example

Normally you would put this command in the rule for the archive file,
and make all the members of the archive file prerequisites of that rule.
For example,

@example
libfoo.a: libfoo.a(x.o) libfoo.a(y.o) @dots{}
        ranlib libfoo.a
@end example

@noindent
The effect of this is to update archive members @file{x.o}, @file{y.o},
etc., and then update the symbol directory member @file{__.SYMDEF} by
running @code{ranlib}.  The rules for updating the members are not shown
here; most likely you can omit them and use the implicit rule which copies
files into the archive, as described in the preceding section.

This is not necessary when using the GNU @code{ar} program, which
updates the @file{__.SYMDEF} member automatically.

@node Archive Pitfalls
@section Dangers When Using Archives
@cindex archive, and parallel execution
@cindex parallel execution, and archive update
@cindex archive, and @code{-j}
@cindex @code{-j}, and archive update

It is important to be careful when using parallel execution (the
@code{-j} switch; @pxref{Parallel, ,Parallel Execution}) and archives.
If multiple @code{ar} commands run at the same time on the same archive
file, they will not know about each other and can corrupt the file.

Possibly a future version of @code{make} will provide a mechanism to
circumvent this problem by serializing all commands that operate on the
same archive file.  But for the time being, you must either write your
makefiles to avoid this problem in some other way, or not use @code{-j}.

@node Archive Suffix Rules, , Archive Pitfalls, Archives
@section Suffix Rules for Archive Files
@cindex suffix rule, for archive
@cindex archive, suffix rule for
@cindex library archive, suffix rule for
@cindex @code{.a} (archives)

You can write a special kind of suffix rule for dealing with archive
files.  @xref{Suffix Rules}, for a full explanation of suffix rules.
Archive suffix rules are obsolete in GNU @code{make}, because pattern
rules for archives are a more general mechanism (@pxref{Archive
Update}).  But they are retained for compatibility with other
@code{make}s.

To write a suffix rule for archives, you simply write a suffix rule
using the target suffix @samp{.a} (the usual suffix for archive files).
For example, here is the old-fashioned suffix rule to update a library
archive from C source files:

@example
@group
.c.a:
        $(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $*.o
        $(AR) r $@@ $*.o
        $(RM) $*.o
@end group
@end example

@noindent
This works just as if you had written the pattern rule:

@example
@group
(%.o): %.c
        $(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $*.o
        $(AR) r $@@ $*.o
        $(RM) $*.o
@end group
@end example

In fact, this is just what @code{make} does when it sees a suffix rule
with @samp{.a} as the target suffix.  Any double-suffix rule
@w{@samp{.@var{x}.a}} is converted to a pattern rule with the target
pattern @samp{(%.o)} and a prerequisite pattern of @samp{%.@var{x}}.

Since you might want to use @samp{.a} as the suffix for some other kind
of file, @code{make} also converts archive suffix rules to pattern rules
in the normal way (@pxref{Suffix Rules}).  Thus a double-suffix rule
@w{@samp{.@var{x}.a}} produces two pattern rules: @samp{@w{(%.o):}
@w{%.@var{x}}} and @samp{@w{%.a}: @w{%.@var{x}}}.@refill

@node Features, Missing, Archives, Top
@chapter Features of GNU @code{make}
@cindex features of GNU @code{make}
@cindex portability
@cindex compatibility

Here is a summary of the features of GNU @code{make}, for comparison
with and credit to other versions of @code{make}.  We consider the
features of @code{make} in 4.2 BSD systems as a baseline.  If you are
concerned with writing portable makefiles, you should not use the
features of @code{make} listed here, nor the ones in @ref{Missing}.

Many features come from the version of @code{make} in System V.

@itemize @bullet
@item
The @code{VPATH} variable and its special meaning.
@xref{Directory Search, , Searching Directories for Prerequisites}.
This feature exists in System V @code{make}, but is undocumented.
It is documented in 4.3 BSD @code{make} (which says it mimics System V's
@code{VPATH} feature).@refill

@item
Included makefiles.  @xref{Include, ,Including Other Makefiles}.
Allowing multiple files to be included with a single directive is a GNU
extension.

@item
Variables are read from and communicated via the environment.
@xref{Environment, ,Variables from the Environment}.

@item
Options passed through the variable @code{MAKEFLAGS} to recursive
invocations of @code{make}.
@xref{Options/Recursion, ,Communicating Options to a Sub-@code{make}}.

@item
The automatic variable @code{$%} is set to the member name
in an archive reference.  @xref{Automatic, ,Automatic Variables}.

@item
The automatic variables @code{$@@}, @code{$*}, @code{$<}, @code{$%},
and @code{$?} have corresponding forms like @code{$(@@F)} and
@code{$(@@D)}.  We have generalized this to @code{$^} as an obvious
extension.  @xref{Automatic, ,Automatic Variables}.@refill

@item
Substitution variable references.
@xref{Reference, ,Basics of Variable References}.

@item
The command-line options @samp{-b} and @samp{-m}, accepted and
ignored.  In System V @code{make}, these options actually do something.

@item
Execution of recursive commands to run @code{make} via the variable
@code{MAKE} even if @samp{-n}, @samp{-q} or @samp{-t} is specified.
@xref{Recursion, ,Recursive Use of @code{make}}.

@item
Support for suffix @samp{.a} in suffix rules.  @xref{Archive Suffix
Rules}.  This feature is obsolete in GNU @code{make}, because the
general feature of rule chaining (@pxref{Chained Rules, ,Chains of
Implicit Rules}) allows one pattern rule for installing members in an
archive (@pxref{Archive Update}) to be sufficient.

@item
The arrangement of lines and backslash-newline combinations in
commands is retained when the commands are printed, so they appear as
they do in the makefile, except for the stripping of initial
whitespace.
@end itemize

The following features were inspired by various other versions of
@code{make}.  In some cases it is unclear exactly which versions inspired
which others.

@itemize @bullet
@item
Pattern rules using @samp{%}.
This has been implemented in several versions of @code{make}.
We're not sure who invented it first, but it's been spread around a bit.
@xref{Pattern Rules, ,Defining and Redefining Pattern Rules}.@refill

@item
Rule chaining and implicit intermediate files.
This was implemented by Stu Feldman in his version of @code{make}
for AT&T Eighth Edition Research Unix, and later by Andrew Hume of
AT&T Bell Labs in his @code{mk} program (where he terms it
``transitive closure'').  We do not really know if
we got this from either of them or thought it up ourselves at the
same time.  @xref{Chained Rules, ,Chains of Implicit Rules}.

@item
The automatic variable @code{$^} containing a list of all prerequisites
of the current target.  We did not invent this, but we have no idea who
did.  @xref{Automatic, ,Automatic Variables}.  The automatic variable
@code{$+} is a simple extension of @code{$^}.

@item
The ``what if'' flag (@samp{-W} in GNU @code{make}) was (as far as we know)
invented by Andrew Hume in @code{mk}.
@xref{Instead of Execution, ,Instead of Executing the Commands}.

@item
The concept of doing several things at once (parallelism) exists in
many incarnations of @code{make} and similar programs, though not in the
System V or BSD implementations.  @xref{Execution, ,Command Execution}.

@item
Modified variable references using pattern substitution come from
SunOS 4.  @xref{Reference, ,Basics of Variable References}.
This functionality was provided in GNU @code{make} by the
@code{patsubst} function before the alternate syntax was implemented
for compatibility with SunOS 4.  It is not altogether clear who
inspired whom, since GNU @code{make} had @code{patsubst} before SunOS
4 was released.@refill

@item
The special significance of @samp{+} characters preceding command lines
(@pxref{Instead of Execution, ,Instead of Executing the Commands}) is
mandated by
@cite{IEEE Standard 1003.2-1992} (POSIX.2).

@item
The @samp{+=} syntax to append to the value of a variable comes from SunOS
4 @code{make}.  @xref{Appending, , Appending More Text to Variables}.

@item
The syntax @w{@samp{@var{archive}(@var{mem1} @var{mem2}@dots{})}} to list
multiple members in a single archive file comes from SunOS 4 @code{make}.
@xref{Archive Members}.

@item
The @code{-include} directive to include makefiles with no error for a
nonexistent file comes from SunOS 4 @code{make}.  (But note that SunOS 4
@code{make} does not allow multiple makefiles to be specified in one
@code{-include} directive.)  The same feature appears with the name
@code{sinclude} in SGI @code{make} and perhaps others.
@end itemize

The remaining features are inventions new in GNU @code{make}:

@itemize @bullet
@item
Use the @samp{-v} or @samp{--version} option to print version and
copyright information.

@item
Use the @samp{-h} or @samp{--help} option to summarize the options to
@code{make}.

@item
Simply-expanded variables.  @xref{Flavors, ,The Two Flavors of Variables}.

@item
Pass command-line variable assignments automatically through the
variable @code{MAKE} to recursive @code{make} invocations.
@xref{Recursion, ,Recursive Use of @code{make}}.

@item
Use the @samp{-C} or @samp{--directory} command option to change
directory.  @xref{Options Summary, ,Summary of Options}.

@item
Make verbatim variable definitions with @code{define}.
@xref{Defining, ,Defining Variables Verbatim}.

@item
Declare phony targets with the special target @code{.PHONY}.

Andrew Hume of AT&T Bell Labs implemented a similar feature with a
different syntax in his @code{mk} program.  This seems to be a case of
parallel discovery.  @xref{Phony Targets, ,Phony Targets}.

@item
Manipulate text by calling functions.
@xref{Functions, ,Functions for Transforming Text}.

@item
Use the @samp{-o} or @samp{--old-file}
option to pretend a file's modification-time is old.
@xref{Avoiding Compilation, ,Avoiding Recompilation of Some Files}.

@item
Conditional execution.

This feature has been implemented numerous times in various versions
of @code{make}; it seems a natural extension derived from the features
of the C preprocessor and similar macro languages and is not a
revolutionary concept.  @xref{Conditionals, ,Conditional Parts of Makefiles}.

@item
Specify a search path for included makefiles.
@xref{Include, ,Including Other Makefiles}.

@item
Specify extra makefiles to read with an environment variable.
@xref{MAKEFILES Variable, ,The Variable @code{MAKEFILES}}.

@item
Strip leading sequences of @samp{./} from file names, so that
@file{./@var{file}} and @file{@var{file}} are considered to be the
same file.@refill

@item
Use a special search method for library prerequisites written in the
form @samp{-l@var{name}}.
@xref{Libraries/Search, ,Directory Search for Link Libraries}.

@item
Allow suffixes for suffix rules
(@pxref{Suffix Rules, ,Old-Fashioned Suffix Rules}) to contain any
characters.  In other versions of @code{make}, they must begin with
@samp{.} and not contain any @samp{/} characters.

@item
Keep track of the current level of @code{make} recursion using the
variable @code{MAKELEVEL}.  @xref{Recursion, ,Recursive Use of @code{make}}.

@item
Provide any goals given on the command line in the variable
@code{MAKECMDGOALS}.  @xref{Goals, ,Arguments to Specify the Goals}.

@item
Specify static pattern rules.  @xref{Static Pattern, ,Static Pattern Rules}.

@item
Provide selective @code{vpath} search.
@xref{Directory Search, ,Searching Directories for Prerequisites}.

@item
Provide computed variable references.
@xref{Reference, ,Basics of Variable References}.

@item
Update makefiles.  @xref{Remaking Makefiles, ,How Makefiles Are Remade}.
System V @code{make} has a very, very limited form of this
functionality in that it will check out SCCS files for makefiles.

@item
Various new built-in implicit rules.
@xref{Catalogue of Rules, ,Catalogue of Implicit Rules}.

@item
The built-in variable @samp{MAKE_VERSION} gives the version number of
@code{make}.
@end itemize

@node Missing, Makefile Conventions, Features, Top
@chapter Incompatibilities and Missing Features
@cindex incompatibilities
@cindex missing features
@cindex features, missing

The @code{make} programs in various other systems support a few features
that are not implemented in GNU @code{make}.  The POSIX.2 standard
(@cite{IEEE Standard 1003.2-1992}) which specifies @code{make} does not
require any of these features.@refill

@itemize @bullet
@item
A target of the form @samp{@var{file}((@var{entry}))} stands for a member
of archive file @var{file}.  The member is chosen, not by name, but by
being an object file which defines the linker symbol @var{entry}.@refill

This feature was not put into GNU @code{make} because of the
nonmodularity of putting knowledge into @code{make} of the internal
format of archive file symbol tables.
@xref{Archive Symbols, ,Updating Archive Symbol Directories}.

@item
Suffixes (used in suffix rules) that end with the character @samp{~}
have a special meaning to System V @code{make};
they refer to the SCCS file that corresponds
to the file one would get without the @samp{~}.  For example, the
suffix rule @samp{.c~.o} would make the file @file{@var{n}.o} from
the SCCS file @file{s.@var{n}.c}.  For complete coverage, a whole
series of such suffix rules is required.
@xref{Suffix Rules, ,Old-Fashioned Suffix Rules}.

In GNU @code{make}, this entire series of cases is handled by two
pattern rules for extraction from SCCS, in combination with the
general feature of rule chaining.
@xref{Chained Rules, ,Chains of Implicit Rules}.

@item
In System V @code{make}, the string @samp{$$@@} has the strange meaning
that, in the prerequisites of a rule with multiple targets, it stands
for the particular target that is being processed.

This is not defined in GNU @code{make} because @samp{$$} should always
stand for an ordinary @samp{$}.

It is possible to get portions of this functionality through the use of
static pattern rules (@pxref{Static Pattern, ,Static Pattern Rules}).
The System V @code{make} rule:

@example
$(targets): $$@@.o lib.a
@end example

@noindent
can be replaced with the GNU @code{make} static pattern rule:

@example
$(targets): %: %.o lib.a
@end example

@item
In System V and 4.3 BSD @code{make}, files found by @code{VPATH} search
(@pxref{Directory Search, ,Searching Directories for Prerequisites}) have their names changed inside command
strings.  We feel it is much cleaner to always use automatic variables
and thus make this feature obsolete.@refill

@item
In some Unix @code{make}s, the automatic variable @code{$*} appearing in
the prerequisites of a rule has the amazingly strange ``feature'' of
expanding to the full name of the @emph{target of that rule}.  We cannot
imagine what went on in the minds of Unix @code{make} developers to do
this; it is utterly inconsistent with the normal definition of @code{$*}.
@vindex * @r{(automatic variable), unsupported bizarre usage}

@item
In some Unix @code{make}s, implicit rule search
(@pxref{Implicit Rules, ,Using Implicit Rules}) is apparently done for
@emph{all} targets, not just those without commands.  This means you can
do:@refill

@example
@group
foo.o:
        cc -c foo.c
@end group
@end example

@noindent
and Unix @code{make} will intuit that @file{foo.o} depends on
@file{foo.c}.@refill

We feel that such usage is broken.  The prerequisite properties of
@code{make} are well-defined (for GNU @code{make}, at least),
and doing such a thing simply does not fit the model.@refill

@item
GNU @code{make} does not include any built-in implicit rules for
compiling or preprocessing EFL programs.  If we hear of anyone who is
using EFL, we will gladly add them.

@item
It appears that in SVR4 @code{make}, a suffix rule can be specified with
no commands, and it is treated as if it had empty commands
(@pxref{Empty Commands}).  For example:

@example
.c.a:
@end example

@noindent
will override the built-in @file{.c.a} suffix rule.

We feel that it is cleaner for a rule without commands to always simply
add to the prerequisite list for the target.  The above example can be
easily rewritten to get the desired behavior in GNU @code{make}:

@example
.c.a: ;
@end example

@item
Some versions of @code{make} invoke the shell with the @samp{-e} flag,
except under @samp{-k} (@pxref{Testing, ,Testing the Compilation of a
Program}).  The @samp{-e} flag tells the shell to exit as soon as any
program it runs returns a nonzero status.  We feel it is cleaner to
write each shell command line to stand on its own and not require this
special treatment.
@end itemize

@comment The makefile standards are in a separate file that is also
@comment included by standards.texi.
@include make-stds.texi

@node Quick Reference, Error Messages, Makefile Conventions, Top
@appendix Quick Reference

This appendix summarizes the directives, text manipulation functions,
and special variables which GNU @code{make} understands.
@xref{Special Targets}, @ref{Catalogue of Rules, ,Catalogue of Implicit Rules},
and @ref{Options Summary, ,Summary of Options},
for other summaries.

Here is a summary of the directives GNU @code{make} recognizes:

@table @code
@item define @var{variable}
@itemx endef

Define a multi-line, recursively-expanded variable.@*
@xref{Sequences}.

@item ifdef @var{variable}
@itemx ifndef @var{variable}
@itemx ifeq (@var{a},@var{b})
@itemx ifeq "@var{a}" "@var{b}"
@itemx ifeq '@var{a}' '@var{b}'
@itemx ifneq (@var{a},@var{b})
@itemx ifneq "@var{a}" "@var{b}"
@itemx ifneq '@var{a}' '@var{b}'
@itemx else
@itemx endif

Conditionally evaluate part of the makefile.@*
@xref{Conditionals}.

@item include @var{file}
@itemx -include @var{file}
@itemx sinclude @var{file}

Include another makefile.@*
@xref{Include, ,Including Other Makefiles}.

@item override @var{variable} = @var{value}
@itemx override @var{variable} := @var{value}
@itemx override @var{variable} += @var{value}
@itemx override @var{variable} ?= @var{value}
@itemx override define @var{variable}
@itemx endef

Define a variable, overriding any previous definition, even one from
the command line.@*
@xref{Override Directive, ,The @code{override} Directive}.

@item export

Tell @code{make} to export all variables to child processes by default.@*
@xref{Variables/Recursion, , Communicating Variables to a Sub-@code{make}}.

@item export @var{variable}
@itemx export @var{variable} = @var{value}
@itemx export @var{variable} := @var{value}
@itemx export @var{variable} += @var{value}
@itemx export @var{variable} ?= @var{value}
@itemx unexport @var{variable}
Tell @code{make} whether or not to export a particular variable to child
processes.@*
@xref{Variables/Recursion, , Communicating Variables to a Sub-@code{make}}.

@item vpath @var{pattern} @var{path}
Specify a search path for files matching a @samp{%} pattern.@*
@xref{Selective Search, , The @code{vpath} Directive}.

@item vpath @var{pattern}
Remove all search paths previously specified for @var{pattern}.

@item vpath
Remove all search paths previously specified in any @code{vpath}
directive.
@end table

Here is a summary of the text manipulation functions (@pxref{Functions}):

@table @code
@item $(subst @var{from},@var{to},@var{text})
Replace @var{from} with @var{to} in @var{text}.@*
@xref{Text Functions, , Functions for String Substitution and Analysis}.

@item $(patsubst @var{pattern},@var{replacement},@var{text})
Replace words matching @var{pattern} with @var{replacement} in @var{text}.@*
@xref{Text Functions, , Functions for String Substitution and Analysis}.

@item $(strip @var{string})
Remove excess whitespace characters from @var{string}.@*
@xref{Text Functions, , Functions for String Substitution and Analysis}.

@item $(findstring @var{find},@var{text})
Locate @var{find} in @var{text}.@*
@xref{Text Functions, , Functions for String Substitution and Analysis}.

@item $(filter @var{pattern}@dots{},@var{text})
Select words in @var{text} that match one of the @var{pattern} words.@*
@xref{Text Functions, , Functions for String Substitution and Analysis}.

@item $(filter-out @var{pattern}@dots{},@var{text})
Select words in @var{text} that @emph{do not} match any of the @var{pattern} words.@*
@xref{Text Functions, , Functions for String Substitution and Analysis}.

@item $(sort @var{list})
Sort the words in @var{list} lexicographically, removing duplicates.@*
@xref{Text Functions, , Functions for String Substitution and Analysis}.

@item $(dir @var{names}@dots{})
Extract the directory part of each file name.@*
@xref{File Name Functions, ,Functions for File Names}.

@item $(notdir @var{names}@dots{})
Extract the non-directory part of each file name.@*
@xref{File Name Functions, ,Functions for File Names}.

@item $(suffix @var{names}@dots{})
Extract the suffix (the last @samp{.} and following characters) of each file name.@*
@xref{File Name Functions, ,Functions for File Names}.

@item $(basename @var{names}@dots{})
Extract the base name (name without suffix) of each file name.@*
@xref{File Name Functions, ,Functions for File Names}.

@item $(addsuffix @var{suffix},@var{names}@dots{})
Append @var{suffix} to each word in @var{names}.@*
@xref{File Name Functions, ,Functions for File Names}.

@item $(addprefix @var{prefix},@var{names}@dots{})
Prepend @var{prefix} to each word in @var{names}.@*
@xref{File Name Functions, ,Functions for File Names}.

@item $(join @var{list1},@var{list2})
Join two parallel lists of words.@*
@xref{File Name Functions, ,Functions for File Names}.

@item $(word @var{n},@var{text})
Extract the @var{n}th word (one-origin) of @var{text}.@*
@xref{File Name Functions, ,Functions for File Names}.

@item $(words @var{text})
Count the number of words in @var{text}.@*
@xref{File Name Functions, ,Functions for File Names}.

@item $(wordlist @var{s},@var{e},@var{text})
Returns the list of words in @var{text} from @var{s} to @var{e}.@*
@xref{File Name Functions, ,Functions for File Names}.

@item $(firstword @var{names}@dots{})
Extract the first word of @var{names}.@*
@xref{File Name Functions, ,Functions for File Names}.

@item $(wildcard @var{pattern}@dots{})
Find file names matching a shell file name pattern (@emph{not} a
@samp{%} pattern).@*
@xref{Wildcard Function, ,The Function @code{wildcard}}.

@item $(error @var{text}@dots{})

When this function is evaluated, @code{make} generates a fatal error
with the message @var{text}.@*
@xref{Make Control Functions, ,Functions That Control Make}.

@item $(warning @var{text}@dots{})

When this function is evaluated, @code{make} generates a warning with
the message @var{text}.@*
@xref{Make Control Functions, ,Functions That Control Make}.

@item $(shell @var{command})

Execute a shell command and return its output.@*
@xref{Shell Function, , The @code{shell} Function}.

@item $(origin @var{variable})

Return a string describing how the @code{make} variable @var{variable} was
defined.@*
@xref{Origin Function, , The @code{origin} Function}.

@item $(foreach @var{var},@var{words},@var{text})

Evaluate @var{text} with @var{var} bound to each word in @var{words},
and concatenate the results.@*
@xref{Foreach Function, ,The @code{foreach} Function}.

@item $(call @var{var},@var{param},@dots{})

Evaluate the variable @var{var} replacing any references to @code{$(1)},
@code{$(2)} with the first, second, etc. @var{param} values.@*
@xref{Call Function, ,The @code{call} Function}.
@end table

Here is a summary of the automatic variables.
@xref{Automatic, ,Automatic Variables},
for full information.

@table @code
@item $@@
The file name of the target.

@item $%
The target member name, when the target is an archive member.

@item $<
The name of the first prerequisite.

@item $?
The names of all the prerequisites that are
newer than the target, with spaces between them.
For prerequisites which are archive members, only
the member named is used (@pxref{Archives}).

@item $^
@itemx $+
The names of all the prerequisites, with spaces between them.  For
prerequisites which are archive members, only the member named is used
(@pxref{Archives}).  The value of @code{$^} omits duplicate
prerequisites, while @code{$+} retains them and preserves their order.

@item $*
The stem with which an implicit rule matches
(@pxref{Pattern Match, ,How Patterns Match}).

@item $(@@D)
@itemx $(@@F)
The directory part and the file-within-directory part of @code{$@@}.

@item $(*D)
@itemx $(*F)
The directory part and the file-within-directory part of @code{$*}.

@item $(%D)
@itemx $(%F)
The directory part and the file-within-directory part of @code{$%}.

@item $(<D)
@itemx $(<F)
The directory part and the file-within-directory part of @code{$<}.

@item $(^D)
@itemx $(^F)
The directory part and the file-within-directory part of @code{$^}.

@item $(+D)
@itemx $(+F)
The directory part and the file-within-directory part of @code{$+}.

@item $(?D)
@itemx $(?F)
The directory part and the file-within-directory part of @code{$?}.
@end table

These variables are used specially by GNU @code{make}:

@table @code
@item MAKEFILES

Makefiles to be read on every invocation of @code{make}.@*
@xref{MAKEFILES Variable, ,The Variable @code{MAKEFILES}}.

@item VPATH

Directory search path for files not found in the current directory.@*
@xref{General Search, , @code{VPATH} Search Path for All Prerequisites}.

@item SHELL

The name of the system default command interpreter, usually @file{/bin/sh}.
You can set @code{SHELL} in the makefile to change the shell used to run
commands.  @xref{Execution, ,Command Execution}.

@item MAKESHELL

On MS-DOS only, the name of the command interpreter that is to be used
by @code{make}. This value takes precedence over the value of
@code{SHELL}.  @xref{Execution, ,MAKESHELL variable}.

@item MAKE

The name with which @code{make} was invoked.
Using this variable in commands has special meaning.
@xref{MAKE Variable, ,How the @code{MAKE} Variable Works}.

@item MAKELEVEL

The number of levels of recursion (sub-@code{make}s).@*
@xref{Variables/Recursion}.

@item MAKEFLAGS

The flags given to @code{make}.  You can set this in the environment or
a makefile to set flags.@*
@xref{Options/Recursion, ,Communicating Options to a Sub-@code{make}}.

It is @emph{never} appropriate to use @code{MAKEFLAGS} directly on a
command line: its contents may not be quoted correctly for use in the
shell.  Always allow recursive @code{make}'s to obtain these values
through the environment from its parent.

@item MAKECMDGOALS

The targets given to @code{make} on the command line.  Setting this
variable has no effect on the operation of @code{make}.@*
@xref{Goals, ,Arguments to Specify the Goals}.

@item CURDIR

Set to the pathname of the current working directory (after all
@code{-C} options are processed, if any).  Setting this variable has no
effect on the operation of @code{make}.@*
@xref{Recursion, ,Recursive Use of @code{make}}.

@item SUFFIXES

The default list of suffixes before @code{make} reads any makefiles.

@item .LIBPATTERNS
Defines the naming of the libraries @code{make} searches for, and their
order.@*
@xref{Libraries/Search, ,Directory Search for Link Libraries}.
@end table

@node Error Messages, Complex Makefile, Quick Reference, Top
@comment  node-name,  next,  previous,  up
@appendix Errors Generated by Make

Here is a list of the more common errors you might see generated by
@code{make}, and some information about what they mean and how to fix
them.

Sometimes @code{make} errors are not fatal, especially in the presence
of a @code{-} prefix on a command script line, or the @code{-k} command
line option.  Errors that are fatal are prefixed with the string
@code{***}.

Error messages are all either prefixed with the name of the program
(usually @samp{make}), or, if the error is found in a makefile, the name
of the file and linenumber containing the problem.

In the table below, these common prefixes are left off.

@table @samp

@item [@var{foo}] Error @var{NN}
@itemx [@var{foo}] @var{signal description}
These errors are not really @code{make} errors at all.  They mean that a
program that @code{make} invoked as part of a command script returned a
non-0 error code (@samp{Error @var{NN}}), which @code{make} interprets
as failure, or it exited in some other abnormal fashion (with a
signal of some type).  @xref{Errors, ,Errors in Commands}.

If no @code{***} is attached to the message, then the subprocess failed
but the rule in the makefile was prefixed with the @code{-} special
character, so @code{make} ignored the error.

@item missing separator.  Stop.
@itemx missing separator (did you mean TAB instead of 8 spaces?).  Stop.
This means that @code{make} could not understand much of anything about
the command line it just read.  GNU @code{make} looks for various kinds
of separators (@code{:}, @code{=}, TAB characters, etc.) to help it
decide what kind of commandline it's seeing.  This means it couldn't
find a valid one.

One of the most common reasons for this message is that you (or perhaps
your oh-so-helpful editor, as is the case with many MS-Windows editors)
have attempted to indent your command scripts with spaces instead of a
TAB character.  In this case, @code{make} will use the second form of
the error above.  Remember that every line in the command script must
begin with a TAB character.  Eight spaces do not count.  @xref{Rule
Syntax}.

@item commands commence before first target.  Stop.
@itemx missing rule before commands.  Stop.
This means the first thing in the makefile seems to be part of a command
script: it begins with a TAB character and doesn't appear to be a legal
@code{make} command (such as a variable assignment).  Command scripts
must always be associated with a target.

The second form is generated if the line has a semicolon as the first
non-whitespace character; @code{make} interprets this to mean you left
out the "target: prerequisite" section of a rule.  @xref{Rule Syntax}.

@item No rule to make target `@var{xxx}'.
@itemx No rule to make target `@var{xxx}', needed by `@var{yyy}'.
This means that @code{make} decided it needed to build a target, but
then couldn't find any instructions in the makefile on how to do that,
either explicit or implicit (including in the default rules database).

If you want that file to be built, you will need to add a rule to your
makefile describing how that target can be built.  Other possible
sources of this problem are typos in the makefile (if that filename is
wrong) or a corrupted source tree (if that file is not supposed to be
built, but rather only a prerequisite).

@item No targets specified and no makefile found.  Stop.
@itemx No targets.  Stop.
The former means that you didn't provide any targets to be built on the
command line, and @code{make} couldn't find any makefiles to read in.
The latter means that some makefile was found, but it didn't contain any
default target and none was given on the command line.  GNU @code{make}
has nothing to do in these situations.
@xref{Makefile Arguments, ,Arguments to Specify the Makefile}.@refill

@item Makefile `@var{xxx}' was not found.
@itemx Included makefile `@var{xxx}' was not found.
A makefile specified on the command line (first form) or included
(second form) was not found.

@item warning: overriding commands for target `@var{xxx}'
@itemx warning: ignoring old commands for target `@var{xxx}'
GNU @code{make} allows commands to be specified only once per target
(except for double-colon rules).  If you give commands for a target
which already has been defined to have commands, this warning is issued
and the second set of commands will overwrite the first set.
@xref{Multiple Rules, ,Multiple Rules for One Target}.

@item Circular @var{xxx} <- @var{yyy} dependency dropped.
This means that @code{make} detected a loop in the dependency graph:
after tracing the prerequisite @var{yyy} of target @var{xxx}, and its
prerequisites, etc., one of them depended on @var{xxx} again.

@item Recursive variable `@var{xxx}' references itself (eventually).  Stop.
This means you've defined a normal (recursive) @code{make} variable
@var{xxx} that, when it's expanded, will refer to itself (@var{xxx}).
This is not allowed; either use simply-expanded variables (@code{:=}) or
use the append operator (@code{+=}).  @xref{Using Variables, ,How to Use
Variables}.

@item Unterminated variable reference.  Stop.
This means you forgot to provide the proper closing parenthesis
or brace in your variable or function reference.

@item insufficient arguments to function `@var{xxx}'.  Stop.
This means you haven't provided the requisite number of arguments for
this function.  See the documentation of the function for a description
of its arguments.  @xref{Functions, ,Functions for Transforming Text}.

@item missing target pattern.  Stop.
@itemx multiple target patterns.  Stop.
@itemx target pattern contains no `%'.  Stop.
These are generated for malformed static pattern rules.  The first means
there's no pattern in the target section of the rule, the second means
there are multiple patterns in the target section, and the third means
the target doesn't contain a pattern character (@code{%}).  @xref{Static
Usage, ,Syntax of Static Pattern Rules}.

@item warning: -jN forced in submake: disabling jobserver mode.
This warning and the next are generated if @code{make} detects error
conditions related to parallel processing on systems where
sub-@code{make}s can communicate (@pxref{Options/Recursion,
,Communicating Options to a Sub-@code{make}}).  This warning is
generated if a recursive invocation of a @code{make} process is forced
to have @samp{-j@var{N}} in its argument list (where @var{N} is greater
than one).  This could happen, for example, if you set the @code{MAKE}
environment variable to @samp{make -j2}.  In this case, the
sub-@code{make} doesn't communicate with other @code{make} processes and
will simply pretend it has two jobs of its own.

@item warning: jobserver unavailable: using -j1.  Add `+' to parent make rule.
In order for @code{make} processes to communicate, the parent will pass
information to the child.  Since this could result in problems if the
child process isn't actually a @code{make}, the parent will only do this
if it thinks the child is a @code{make}.  The parent uses the normal
algorithms to determine this (@pxref{MAKE Variable, ,How the @code{MAKE}
Variable Works}).  If the makefile is constructed such that the parent
doesn't know the child is a @code{make} process, then the child will
receive only part of the information necessary.  In this case, the child
will generate this warning message and proceed with its build in a
sequential manner.

@end table

@node Complex Makefile, Concept Index, Error Messages, Top
@appendix Complex Makefile Example

Here is the makefile for the GNU @code{tar} program.  This is a
moderately complex makefile.

Because it is the first target, the default goal is @samp{all}.  An
interesting feature of this makefile is that @file{testpad.h} is a
source file automatically created by the @code{testpad} program,
itself compiled from @file{testpad.c}.

If you type @samp{make} or @samp{make all}, then @code{make} creates
the @file{tar} executable, the @file{rmt} daemon that provides
remote tape access, and the @file{tar.info} Info file.

If you type @samp{make install}, then @code{make} not only creates
@file{tar}, @file{rmt}, and @file{tar.info}, but also installs
them.

If you type @samp{make clean}, then @code{make} removes the @samp{.o}
files, and the @file{tar}, @file{rmt}, @file{testpad},
@file{testpad.h}, and @file{core} files.

If you type @samp{make distclean}, then @code{make} not only removes
the same files as does @samp{make clean} but also the
@file{TAGS}, @file{Makefile}, and @file{config.status} files.
(Although it is not evident, this makefile (and
@file{config.status}) is generated by the user with the
@code{configure} program, which is provided in the @code{tar}
distribution, but is not shown here.)

If you type @samp{make realclean}, then @code{make} removes the same
files as does @samp{make distclean} and also removes the Info files
generated from @file{tar.texinfo}.

In addition, there are targets @code{shar} and @code{dist} that create
distribution kits.

@example
@group
# Generated automatically from Makefile.in by configure.
# Un*x Makefile for GNU tar program.
# Copyright (C) 1991 Free Software Foundation, Inc.
@end group

@group
# This program is free software; you can redistribute
# it and/or modify it under the terms of the GNU
# General Public License @dots{}
@dots{}
@dots{}
@end group

SHELL = /bin/sh

#### Start of system configuration section. ####

srcdir = .

@group
# If you use gcc, you should either run the
# fixincludes script that comes with it or else use
# gcc with the -traditional option.  Otherwise ioctl
# calls will be compiled incorrectly on some systems.
CC = gcc -O
YACC = bison -y
INSTALL = /usr/local/bin/install -c
INSTALLDATA = /usr/local/bin/install -c -m 644
@end group

# Things you might add to DEFS:
# -DSTDC_HEADERS        If you have ANSI C headers and
#                       libraries.
# -DPOSIX               If you have POSIX.1 headers and
#                       libraries.
# -DBSD42               If you have sys/dir.h (unless
#                       you use -DPOSIX), sys/file.h,
#                       and st_blocks in `struct stat'.
# -DUSG                 If you have System V/ANSI C
#                       string and memory functions
#                       and headers, sys/sysmacros.h,
#                       fcntl.h, getcwd, no valloc,
#                       and ndir.h (unless
#                       you use -DDIRENT).
# -DNO_MEMORY_H         If USG or STDC_HEADERS but do not
#                       include memory.h.
# -DDIRENT              If USG and you have dirent.h
#                       instead of ndir.h.
# -DSIGTYPE=int         If your signal handlers
#                       return int, not void.
# -DNO_MTIO             If you lack sys/mtio.h
#                       (magtape ioctls).
# -DNO_REMOTE           If you do not have a remote shell
#                       or rexec.
# -DUSE_REXEC           To use rexec for remote tape
#                       operations instead of
#                       forking rsh or remsh.
# -DVPRINTF_MISSING     If you lack vprintf function
#                       (but have _doprnt).
# -DDOPRNT_MISSING      If you lack _doprnt function.
#                       Also need to define
#                       -DVPRINTF_MISSING.
# -DFTIME_MISSING       If you lack ftime system call.
# -DSTRSTR_MISSING      If you lack strstr function.
# -DVALLOC_MISSING      If you lack valloc function.
# -DMKDIR_MISSING       If you lack mkdir and
#                       rmdir system calls.
# -DRENAME_MISSING      If you lack rename system call.
# -DFTRUNCATE_MISSING   If you lack ftruncate
#                       system call.
# -DV7                  On Version 7 Unix (not
#                       tested in a long time).
# -DEMUL_OPEN3          If you lack a 3-argument version
#                       of open, and want to emulate it
#                       with system calls you do have.
# -DNO_OPEN3            If you lack the 3-argument open
#                       and want to disable the tar -k
#                       option instead of emulating open.
# -DXENIX               If you have sys/inode.h
#                       and need it 94 to be included.

DEFS =  -DSIGTYPE=int -DDIRENT -DSTRSTR_MISSING \
        -DVPRINTF_MISSING -DBSD42
# Set this to rtapelib.o unless you defined NO_REMOTE,
# in which case make it empty.
RTAPELIB = rtapelib.o
LIBS =
DEF_AR_FILE = /dev/rmt8
DEFBLOCKING = 20

@group
CDEBUG = -g
CFLAGS = $(CDEBUG) -I. -I$(srcdir) $(DEFS) \
        -DDEF_AR_FILE=\"$(DEF_AR_FILE)\" \
        -DDEFBLOCKING=$(DEFBLOCKING)
LDFLAGS = -g
@end group

@group
prefix = /usr/local
# Prefix for each installed program,
# normally empty or `g'.
binprefix =

# The directory to install tar in.
bindir = $(prefix)/bin

# The directory to install the info files in.
infodir = $(prefix)/info
@end group

#### End of system configuration section. ####

SRC1 =  tar.c create.c extract.c buffer.c \
        getoldopt.c update.c gnu.c mangle.c
SRC2 =  version.c list.c names.c diffarch.c \
        port.c wildmat.c getopt.c
SRC3 =  getopt1.c regex.c getdate.y
SRCS =  $(SRC1) $(SRC2) $(SRC3)
OBJ1 =  tar.o create.o extract.o buffer.o \
        getoldopt.o update.o gnu.o mangle.o
OBJ2 =  version.o list.o names.o diffarch.o \
        port.o wildmat.o getopt.o
OBJ3 =  getopt1.o regex.o getdate.o $(RTAPELIB)
OBJS =  $(OBJ1) $(OBJ2) $(OBJ3)
@group
AUX =   README COPYING ChangeLog Makefile.in  \
        makefile.pc configure configure.in \
        tar.texinfo tar.info* texinfo.tex \
        tar.h port.h open3.h getopt.h regex.h \
        rmt.h rmt.c rtapelib.c alloca.c \
        msd_dir.h msd_dir.c tcexparg.c \
        level-0 level-1 backup-specs testpad.c
@end group

all:    tar rmt tar.info

@group
tar:    $(OBJS)
        $(CC) $(LDFLAGS) -o $@@ $(OBJS) $(LIBS)
@end group

@group
rmt:    rmt.c
        $(CC) $(CFLAGS) $(LDFLAGS) -o $@@ rmt.c
@end group

@group
tar.info: tar.texinfo
        makeinfo tar.texinfo
@end group

@group
install: all
        $(INSTALL) tar $(bindir)/$(binprefix)tar
        -test ! -f rmt || $(INSTALL) rmt /etc/rmt
        $(INSTALLDATA) $(srcdir)/tar.info* $(infodir)
@end group

@group
$(OBJS): tar.h port.h testpad.h
regex.o buffer.o tar.o: regex.h
# getdate.y has 8 shift/reduce conflicts.
@end group

@group
testpad.h: testpad
        ./testpad
@end group

@group
testpad: testpad.o
        $(CC) -o $@@ testpad.o
@end group

@group
TAGS:   $(SRCS)
        etags $(SRCS)
@end group

@group
clean:
        rm -f *.o tar rmt testpad testpad.h core
@end group

@group
distclean: clean
        rm -f TAGS Makefile config.status
@end group

@group
realclean: distclean
        rm -f tar.info*
@end group

@group
shar: $(SRCS) $(AUX)
        shar $(SRCS) $(AUX) | compress \
          > tar-`sed -e '/version_string/!d' \
                     -e 's/[^0-9.]*\([0-9.]*\).*/\1/' \
                     -e q
                     version.c`.shar.Z
@end group

@group
dist: $(SRCS) $(AUX)
        echo tar-`sed \
             -e '/version_string/!d' \
             -e 's/[^0-9.]*\([0-9.]*\).*/\1/' \
             -e q
             version.c` > .fname
        -rm -rf `cat .fname`
        mkdir `cat .fname`
        ln $(SRCS) $(AUX) `cat .fname`
        tar chZf `cat .fname`.tar.Z `cat .fname`
        -rm -rf `cat .fname` .fname
@end group

@group
tar.zoo: $(SRCS) $(AUX)
        -rm -rf tmp.dir
        -mkdir tmp.dir
        -rm tar.zoo
        for X in $(SRCS) $(AUX) ; do \
            echo $$X ; \
            sed 's/$$/^M/' $$X \
            > tmp.dir/$$X ; done
        cd tmp.dir ; zoo aM ../tar.zoo *
        -rm -rf tmp.dir
@end group
@end example

@node Concept Index, Name Index, Complex Makefile, Top
@unnumbered Index of Concepts

@printindex cp

@node Name Index,  , Concept Index, Top
@unnumbered Index of Functions, Variables, & Directives

@printindex fn

@summarycontents
@contents
@bye