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Multiple Targets in a Rule
A rule with multiple targets is equivalent to writing many rules,
each with one target, and all identical aside from that. The same
commands apply to all the targets, but their effects may vary because
you can substitute the actual target name into the command using `$@'.
The rule contributes the same dependencies to all the targets also.
This is useful in two cases.
* You want just dependencies, no commands. For example:
kbd.o command.o files.o: command.h
gives an additional dependency to each of the three object files
* Similar commands work for all the targets. The commands do not
need to be absolutely identical, since the automatic variable `$@'
can be used to substitute the particular target to be remade into
the commands (Note: Automatic Variables.). For example:
bigoutput littleoutput : text.g
generate text.g -$(subst output,,$@) > $@
is equivalent to
bigoutput : text.g
generate text.g -big > bigoutput
littleoutput : text.g
generate text.g -little > littleoutput
Here we assume the hypothetical program `generate' makes two types
of output, one if given `-big' and one if given `-little'. *Note
Functions for String Substitution and Analysis: Text Functions,
for an explanation of the `subst' function.
Suppose you would like to vary the dependencies according to the
target, much as the variable `$@' allows you to vary the commands. You
cannot do this with multiple targets in an ordinary rule, but you can
do it with a "static pattern rule". Note: Static Pattern Rules
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