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Date: Sun, 13 Feb 2005 11:51:09 +0100 (CET)
From: Harti Brandt <hartmut.brandt@dlr.de>
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To: Kris Kennaway <kris@obsecurity.org>
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cc: hackers@FreeBSD.org
Subject: Re: Makefile .for and .if expansion
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On Sat, 12 Feb 2005, Kris Kennaway wrote:

KK>The following small makefile doesn't behave as one would naively
KK>expect:
KK>
KK>MANLANG?=foo ""
KK>all:
KK>.for i in ${MANLANG}
KK>.if empty(${i})
KK>        @echo foo ${i}
KK>.endif
KK>.endfor
KK>
KK>ports-i386%make
KK>foo foo
KK>foo
KK>
KK>I think this is because the .if evaluation is happening too early, and
KK>it's not being done after the .for loop is expanded and the i variable
KK>is set.
KK>
KK>In order to get this to work I seem to have to do the following:
KK>
KK>MANLANG?=foo ""
KK>.for i in ${MANLANG}
KK>j=      ${i}
KK>.if (${j} != "\"\"")
KK>.for l in ${j}
KK>k+=     ${l}
KK>.endfor
KK>.endif
KK>.endfor
KK>all:
KK>        @echo ${k}
KK>
KK>ports-i386%make
KK>foo
KK>
KK>If I remove the inner .for it breaks, and if I remove the j assignment
KK>it breaks.  Also if I try and remove the use of k and put an echo
KK>inside the inner .for (with the all: preceding the whole loop) it
KK>breaks.
KK>
KK>This is extremely nasty.
KK>
KK>Am I missing an easier way to do this?

As far as I can see you just discovered the limitation of make that is 
documented under the BUGs section in the man page. This is the result of 
the quit simple minded .for implementation (it's basically like expanding 
a macro).

harti