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-rw-r--r--doc/make.texi66
1 files changed, 42 insertions, 24 deletions
diff --git a/doc/make.texi b/doc/make.texi
index 2efcca0..3c01e0a 100644
--- a/doc/make.texi
+++ b/doc/make.texi
@@ -308,7 +308,7 @@ 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
+* Automatic Variables:: 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
@@ -1776,7 +1776,7 @@ print: *.c
This rule uses @file{print} as an empty target file; see @ref{Empty
Targets, ,Empty Target Files to Record Events}. (The automatic variable
@samp{$?} is used to print only those files that have changed; see
-@ref{Automatic, ,Automatic Variables}.)@refill
+@ref{Automatic Variables}.)@refill
Wildcard expansion does not happen when you define a variable. Thus, if
you write this:
@@ -2171,7 +2171,7 @@ Therefore, you must write the commands with care so that they will look for
the prerequisite in the directory where @code{make} finds it.
This is done with the @dfn{automatic variables} such as @samp{$^}
-(@pxref{Automatic, ,Automatic Variables}).
+(@pxref{Automatic Variables}).
For instance, the value of @samp{$^} is a
list of all the prerequisites of the rule, including the names of
the directories in which they were found, and the value of
@@ -2514,7 +2514,7 @@ print: foo.c bar.c
With this rule, @samp{make print} will execute the @code{lpr} command if
either source file has changed since the last @samp{make print}. The
automatic variable @samp{$?} is used to print only those files that have
-changed (@pxref{Automatic, ,Automatic Variables}).
+changed (@pxref{Automatic Variables}).
@node Special Targets, Multiple Targets, Empty Targets, Rules
@section Special Built-in Target Names
@@ -2724,7 +2724,7 @@ mentioned.
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:
+commands (@pxref{Automatic Variables}). For example:
@example
@group
@@ -2912,7 +2912,7 @@ $(objects): %.o: %.c
@noindent
Here @samp{$<} is the automatic variable that holds the name of the
prerequisite and @samp{$@@} is the automatic variable that holds the name
-of the target; see @ref{Automatic, , Automatic Variables}.
+of the target; see @ref{Automatic Variables}.
Each target specified must match the target pattern; a warning is issued
for each target that does not. If you have a list of files, only some of
@@ -4234,7 +4234,7 @@ command options (@pxref{Overriding, ,Overriding Variables}).
A few variables have names that are a single punctuation character or
just a few characters. These are the @dfn{automatic variables}, and
-they have particular specialized uses. @xref{Automatic, ,Automatic Variables}.
+they have particular specialized uses. @xref{Automatic Variables}.
@menu
* Reference:: How to use the value of a variable.
@@ -4303,7 +4303,7 @@ A dollar sign followed by a character other than a dollar sign,
open-parenthesis or open-brace treats that single character as the
variable name. Thus, you could reference the variable @code{x} with
@samp{$x}. However, this practice is strongly discouraged, except in
-the case of the automatic variables (@pxref{Automatic, ,Automatic Variables}).
+the case of the automatic variables (@pxref{Automatic Variables}).
@node Flavors, Advanced, Reference, Using Variables
@section The Two Flavors of Variables
@@ -4787,7 +4787,7 @@ Variables in the environment become @code{make} variables.
@item
Several @dfn{automatic} variables are given new values for each rule.
Each of these has a single conventional use.
-@xref{Automatic, ,Automatic Variables}.
+@xref{Automatic Variables}.
@item
Several variables have constant initial values.
@@ -4835,7 +4835,7 @@ 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}).
+@dfn{automatic} variables (@pxref{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
@@ -5173,7 +5173,7 @@ MS-DOS}.)@refill
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}).
+(@pxref{Automatic Variables}).
The other exception is @dfn{target-specific variable values}. This
feature allows you to define different values for the same variable,
@@ -5194,6 +5194,13 @@ or like this:
@var{target} @dots{} : override @var{variable-assignment}
@end example
+@noindent
+or like this:
+
+@example
+@var{target} @dots{} : export @var{variable-assignment}
+@end example
+
Multiple @var{target} values create a target-specific variable value for
each member of the target list individually.
@@ -5515,7 +5522,7 @@ 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}).
+(@pxref{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
@@ -6517,7 +6524,7 @@ makefile (@pxref{Override Directive, ,The @code{override} Directive}).
if @var{variable} is an automatic variable defined for the
execution of the commands for each rule
-(@pxref{Automatic, , Automatic Variables}).
+(@pxref{Automatic Variables}).
@end table
This information is primarily useful (other than for your curiosity) to
@@ -8185,7 +8192,7 @@ 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
+* Automatic Variables:: 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
@@ -8263,7 +8270,7 @@ 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
+@node Pattern Examples, Automatic Variables, Pattern Intro, Pattern Rules
@subsection Pattern Rule Examples
Here are some examples of pattern rules actually predefined in
@@ -8279,7 +8286,7 @@ files:@refill
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
+in each case where the rule applies (@pxref{Automatic Variables}).@refill
Here is a second built-in rule:
@@ -8320,7 +8327,7 @@ 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
+@node Automatic Variables, Pattern Match, Pattern Examples, Pattern Rules
@subsection Automatic Variables
@cindex automatic variables
@cindex variables, automatic
@@ -8337,6 +8344,17 @@ 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.
+@cindex automatic variables in prerequisites
+@cindex prerequisites, and automatic variables
+It's very important that you recognize the limited scope in which
+automatic variable values are available: they only have values within
+the command script. In particular, you cannot use them anywhere
+within the target or prerequisite lists of a rule; they have no value
+there and will expand to the empty string. A common mistake is
+attempting to use @code{$@@} within the prerequisites list in a rule;
+this will not work. However, see below for information on the
+SysV-style @code{$$@@} variables.
+
Here is a table of automatic variables:
@table @code
@@ -8551,7 +8569,7 @@ compatibility with SysV makefiles. In a native GNU @code{make} file
there are other ways to accomplish the same results. This feature is
disabled if the special pseudo target @code{.POSIX} is defined.
-@node Pattern Match, Match-Anything Rules, Automatic, Pattern Rules
+@node Pattern Match, Match-Anything Rules, Automatic Variables, Pattern Rules
@subsection How Patterns Match
@cindex stem
@@ -8930,7 +8948,7 @@ 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}.
+@xref{Automatic Variables}.
@node Archives, Features, Implicit Rules, Top
@chapter Using @code{make} to Update Archive Files
@@ -9033,7 +9051,7 @@ 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{$%}. @xref{Automatic, ,Automatic Variables}.
+@samp{$%}. @xref{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
@@ -9196,13 +9214,13 @@ invocations of @code{make}.
@item
The automatic variable @code{$%} is set to the member name
-in an archive reference. @xref{Automatic, ,Automatic Variables}.
+in an archive reference. @xref{Automatic Variables}.
@item
The automatic variables @code{$@@}, @code{$*}, @code{$<}, @code{$%},
and @code{$?} have corresponding forms like @code{$(@@F)} and
@code{$(@@D)}. We have generalized this to @code{$^} as an obvious
-extension. @xref{Automatic, ,Automatic Variables}.@refill
+extension. @xref{Automatic Variables}.@refill
@item
Substitution variable references.
@@ -9254,7 +9272,7 @@ same time. @xref{Chained Rules, ,Chains of Implicit Rules}.
@item
The automatic variable @code{$^} 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
+did. @xref{Automatic Variables}. The automatic variable
@code{$+} is a simple extension of @code{$^}.
@item
@@ -9711,7 +9729,7 @@ Evaluate the variable @var{var} replacing any references to @code{$(1)},
@end table
Here is a summary of the automatic variables.
-@xref{Automatic, ,Automatic Variables},
+@xref{Automatic Variables},
for full information.
@table @code