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 ‘$@’. The rule contributes the same prerequisites to all the targets also.
This is useful in two cases.
kbd.o command.o files.o: command.h
gives an additional prerequisite to each of the three object files mentioned.
bigoutput littleoutput : text.g generate text.g -$(subst output,,$@) > $@
is equivalent to
bigoutput : text.g generate text.g -big > bigoutput littleoutput : text.g generate text.g -little > littleoutput
Here we assume the hypothetical program
generate makes two
types of output, one if given ‘-big’ and one if given
See Functions for String Substitution and Analysis,
for an explanation of the
Suppose you would like to vary the prerequisites according to the target, much as the variable ‘$@’ 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. See Static Pattern Rules.