(make.info)Wildcard Function


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The Function `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 `wildcard' function, like
this:

     $(wildcard PATTERN...)

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 `wildcard'
function.  Note that this is different from how unmatched wildcards
behave in rules, where they are used verbatim rather than ignored
(Note: Wildcard Pitfall.).

   One use of the `wildcard' function is to get a list of all the C
source files in a directory, like this:

     $(wildcard *.c)

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

     $(patsubst %.c,%.o,$(wildcard *.c))

(Here we have used another function, `patsubst'.  Note: Functions for
String Substitution and Analysis.)

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

     objects := $(patsubst %.c,%.o,$(wildcard *.c))
     
     foo : $(objects)
             cc -o foo $(objects)

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


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