Next: Wildcard Pitfall Up: Wildcards
Wildcards can be used in the commands of a rule, where they are
expanded by the shell. For example, here is a rule to delete all the
rm -f *.o
Wildcards are also useful in the dependencies of a rule. With the
following rule in the makefile, `make print' will print all the `.c'
files that have changed since the last time you printed them:
lpr -p $?
This rule uses `print' as an empty target file; see Note: Empty Target
Files to Record Events. (The automatic variable `$?' is
used to print only those files that have changed; see Note: Automatic
Wildcard expansion does not happen when you define a variable.
Thus, if you write this:
objects = *.o
then the value of the variable `objects' is the actual string `*.o'.
However, if you use the value of `objects' in a target, dependency or
command, wildcard expansion will take place at that time. To set
`objects' to the expansion, instead use:
objects := $(wildcard *.o)
Note: Wildcard Function.
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