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| -rw-r--r-- | make.texinfo | 72 |
1 files changed, 71 insertions, 1 deletions
diff --git a/make.texinfo b/make.texinfo index 298d713..8675d66 100644 --- a/make.texinfo +++ b/make.texinfo @@ -6,7 +6,10 @@ $Header$ $Log$ -Revision 1.53 1988/06/03 00:07:30 mcgrath +Revision 1.54 1988/06/10 11:43:00 mcgrath +Added more stuff about `foreach'. + +Revision 1.53 88/06/03 00:07:30 mcgrath * Fixed a typo in the `Missing' section. * Added an example of how to replace the System V $$@ feature using static pattern rules. @@ -2713,6 +2716,73 @@ For this to work properly, you must use a recursively expanded variable, so it will be expanded when the @code{foreach} function is invoked, not when the variable is defined.@refill +This simple example sets the variable @samp{files} to the list of +all files in the directories in the list @samp{dirs}. + +@example +find_files = $(wildcard $(dir)/*) +dirs := a b c d +files := $(foreach dir,$(dirs),$(find_files)) +@end example + +Note that the variable @samp{find_files} is made recursive. It is then +used to perform a function that results in a value, rather than to simply +@emph{be} a value. This example has the same result (except for setting +@samp{find_files} and @samp{dirs}) as: + +@example +files := $(wildcard a/* b/* c/* d/*) +dir = +@end example + +The variable @samp{dir} is made a recursive variable with a null value by +virtue of not being set beforehand, and then being used in the +@code{foreach} function. If, before the invokation of @code{foreach}, +@samp{dir} had been defined by the line: + +@example +dir := foo +@end example + +@noindent +then it would have that same value and the property of being a simply +expanded variable after the @code{foreach} function was finished. +Note also that @samp{dir} would remain a simply expanded variable +throughout the invokation of @code{foreach}. + +Because it is expanded before other processing is done, the @var{var} +argument to @code{foreach} need not be a variable name. It can be a +variable expression resulting in the name. Thus, + +@example +dir := a +var = $(whatsthevar) +foo := dar +whatsthevar := $(subst a,i,$(foo)) +files := $(foreach $(var),$(dirs),$(find_files)) +@end example + +@noindent +is ultimately equivalent to the first example. You must take care when +using complex variable expressions that result in variable names because +many strange things are legal variable names, and these might not be what +you intended. For example, + +@example +files := $(foreach Es escrito en espanol!,b c ch,$(find_files)) +@end example + +@noindent +will work as expected if @samp{find_files} references the variable +@samp{Es escrito en espanol!} (es un nombre bastante largo, no?), but +somehow this seems unlikely (pero qualquiera cosa es posible). +You might be inclined to use variable names such as this so as not to +disturb other variables, because variables with names containing whitespace +can be referenced but not defined in the conventional manner +(@pxref{Defining}). But this is not necessary, since the @code{foreach} +function always preserves the value and flavor (@pxref{Flavors}) of its +control variable (the one named by the @var{var} argument).@refill + @node Filename Functions,, Foreach Function, Functions @section Functions for File Names |