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