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Rules with multiple outputs

From: Lane Schwartz
Subject: Rules with multiple outputs
Date: Mon, 12 Apr 2010 09:22:35 -0500


I am trying to solve an issue regarding rules with multiple outputs. I would 
like my makefile to correctly handle these rules, so that the generating 
commands are only run once, even when make is run with -j (for parallel). I am 
aware that a solution to handle this is using pattern rules, as in the case 
when generating files using bison (section 10.5.2 GNU Make manual). But, in my 
case the targets that are generated tend not to share named patterns.

Here's an example of what I would like to do:

a b c: d
        foo d

When command 'foo' is run, it generates files a, b, and c. The problem here is 
that if the make file is run with -j, there is a good chance that foo will be 
run multiple times, since make treats the above command as equivalent to the 
three commands below:

a: d
        foo d

b: d
        foo d

c: d
        foo d

If a command produces multiple outputs that share a common pattern in their 
name, the solution below becomes possible, and make handles this properly when 
-j is used.

%.x %.y %.z: %.q
        bar $<

This is the solution described in section 10.5.2 of the GNU Make manual, as 
well as at
 Is anyone aware of a general solution for this problem, where running a 
command produces multiple output files that do not share a common pattern in 
their names?

I suspect that no elegant general solution exists. If that is the case, I would 
be interested in proposing an extension to make to allow for this 
functionality, and would be willing to help implement it. I'm not familiar with 
the GNU make developer community, so any pointers to the appropriate person or 
persons to discuss such ideas would be greatly appreciated.


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