File: make.info,  Node: Wildcard Function,  Prev: Wildcard Pitfall,  Up: Wildcards

4.4.3 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::).

   As with wildcard expansion in rules, the results of the 'wildcard'
function are sorted.  But again, each individual expression is sorted
separately, so '$(wildcard *.c *.h)' will expand to all files matching
'.c', sorted, followed by all files matching '.h', sorted.

   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 '.c' suffix with '.o' in the result, like this:

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

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

   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: Flavors, for an explanation of ':=', which
is a variant of '='.)