[ << ] | [ < ] | [ Up ] | [ > ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
4.10 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 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 (see section Automatic Variables). For example:
bigoutput littleoutput : text.g generate text.g -$(subst output,,$@) > $@
is equivalent to
bigoutput : text.g generate text.g -big > bigoutput littleoutput : text.g generate text.g -little > littleoutput
Here we assume the hypothetical program
generate
makes two types of output, one if given ‘-big’ and one if given ‘-little’. See section Functions for String Substitution and Analysis, for an explanation of thesubst
function.
Suppose you would like to vary the prerequisites according to the target, much as the variable ‘$@’ 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. See section Static Pattern Rules.
[ << ] | [ < ] | [ Up ] | [ > ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
This document was generated on October 10, 2013 using texi2html 5.0.