Info Catalog make: Wildcard Pitfall make: Wildcards

make: Wildcard Function

 
 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 (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 '.c' suffix with '.o' in the result, like this:
 
      $(patsubst %.c,%.o,$(wildcard *.c))
 
 (Here we have used another function, 'patsubst'.  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.  
 The Two Flavors of Variables Flavors, for an explanation of ':=', which
 is a variant of '='.)
 

Info Catalog make: Wildcard Pitfall make: Wildcards