diff options
Diffstat (limited to 'doc/make.texi')
| -rw-r--r-- | doc/make.texi | 67 |
1 files changed, 43 insertions, 24 deletions
diff --git a/doc/make.texi b/doc/make.texi index 21f0270..4c0fe44 100644 --- a/doc/make.texi +++ b/doc/make.texi @@ -240,6 +240,7 @@ How to Use Variables basis. * Pattern-specific:: Target-specific variable values can be applied to a group of targets that match a pattern. +* Suppressing Inheritance:: Suppress inheritance of variables. * Special Variables:: Variables with special meaning or behavior. Advanced Features for Reference to Variables @@ -4691,6 +4692,7 @@ they have particular specialized uses. @xref{Automatic Variables}. basis. * Pattern-specific:: Target-specific variable values can be applied to a group of targets that match a pattern. +* Suppressing Inheritance:: Suppress inheritance of variables. * Special Variables:: Variables with special meaning or behavior. @end menu @@ -5625,19 +5627,9 @@ Set a target-specific variable value like this: @var{target} @dots{} : @var{variable-assignment} @end example -@noindent -or like this: - -@example -@var{target} @dots{} : override @var{variable-assignment} -@end example - -@noindent -or like this: - -@example -@var{target} @dots{} : export @var{variable-assignment} -@end example +Target-specific variable assignments can be prefixed with any or all of the +special keywords @code{export}, @code{override}, or @code{private}; +these apply their normal behavior to this instance of the variable only. Multiple @var{target} values create a target-specific variable value for each member of the target list individually. @@ -5683,7 +5675,7 @@ will cause that prerequisite to be built and the prerequisite will inherit the target-specific value from the first target. It will ignore the target-specific values from any other targets. -@node Pattern-specific, Special Variables, Target-specific, Using Variables +@node Pattern-specific, Suppressing Inheritance, Target-specific, Using Variables @section Pattern-specific Variable Values @cindex pattern-specific variables @cindex variables, pattern-specific @@ -5704,15 +5696,6 @@ 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 @@ -5729,7 +5712,43 @@ For example: will assign @code{CFLAGS} the value of @samp{-O} for all targets matching the pattern @code{%.o}. -@node Special Variables, , Pattern-specific, Using Variables +@node Suppressing Inheritance, Special Variables, Pattern-specific, Using Variables +@section Suppressing Inheritance +@findex private +@cindex suppressing inheritance +@cindex inheritance, suppressing + +As described in previous sections, @code{make} variables are inherited +by prerequisites. This capability allows you to modify the behavior +of a prerequisite based on which targets caused it to be rebuilt. For +example, you might set a target-specific variable on a @code{debug} +target, then running @samp{make debug} will cause that variable to be +inherited by all prerequisites of @code{debug}, while just running +@samp{make all} (for example) would not have that assignment. + +Sometimes, however, you may not want a variable to be inherited. For +these situations, @code{make} provides the @code{private} modifier. +Although this modifier can be used with any variable assignment, it +makes the most sense with target- and pattern-specific variables. Any +variable marked @code{private} will be visible to its local target but +will not be inherited by prerequisites of that target. A global +variable marked @code{private} will be visible in the global scope but +will not be inherited by any target, and hence will not be visible +in any recipe. + +As an example, consider this makefile: +@example +EXTRA_CFLAGS = + +prog: private EXTRA_CFLAGS = -L/usr/local/lib +prog: a.o b.o +@end example + +Due to the @code{private} modifier, @code{a.o} and @code{b.o} will not +inherit the @code{EXTRA_CFLAGS} variable assignment from the +@code{progs} target. + +@node Special Variables, , Suppressing Inheritance, Using Variables @comment node-name, next, previous, up @section Other Special Variables @cindex makefiles, and special variables |