Date: Sun, 13 Feb 2005 13:10:33 +0200 From: Ruslan Ermilov <ru@freebsd.org> To: Kris Kennaway <kris@obsecurity.org> Cc: hackers@freebsd.org Subject: Re: Makefile .for and .if expansion Message-ID: <20050213111033.GB88954@ip.net.ua> In-Reply-To: <20050213023201.GB24426@xor.obsecurity.org> References: <20050213023201.GB24426@xor.obsecurity.org>
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Hi Kris,
On Sat, Feb 12, 2005 at 06:32:01PM -0800, Kris Kennaway wrote:
> The following small makefile doesn't behave as one would naively
> expect:
>=20
> MANLANG?=3Dfoo ""
> all:
> .for i in ${MANLANG}
> .if empty(${i})
> @echo foo ${i}
> .endif
> .endfor
>=20
> ports-i386%make
> foo foo
> foo
>=20
> I think this is because the .if evaluation is happening too early, and
> it's not being done after the .for loop is expanded and the i variable
> is set.
>=20
This makefile is broken, you're abusing empty(). empty() expects
a variable name (without `$') as an argument, and ``.if empty(foo)''
means "true if ${foo} has an empty value". Note that in 4.x, "foo"
also needs to be a defined variable, for this to work at all. In
5.x and 6.x, undefined variables are treated like empty variable
by empty().
> In order to get this to work I seem to have to do the following:
>=20
> MANLANG?=3Dfoo ""
> .for i in ${MANLANG}
> j=3D ${i}
> .if (${j} !=3D "\"\"")
> .for l in ${j}
> k+=3D ${l}
> .endfor
> .endif
> .endfor
> all:
> @echo ${k}
>=20
> ports-i386%make
> foo
>=20
> If I remove the inner .for it breaks, and if I remove the j assignment
> it breaks. Also if I try and remove the use of k and put an echo
> inside the inner .for (with the all: preceding the whole loop) it
> breaks.
>=20
> This is extremely nasty.
>=20
Yes. This behavior is documented in the BUGS section of the make(1)
manpage: .for loops are unrolled before tests, and .for variables
aren't real variables, so a fragment like this:
=2Efor i in foo bar
=2Eif ${i} =3D=3D "foo"
echo ${i}
=2Eendif
=2Eendfor
doesn't work. This fragment is rewritten by make(1) before further
parsing as follows:
=2Eif foo =3D=3D "foo"
echo foo
=2Eendif
=2Eif bar =3D=3D "foo"
echo bar
=2Eendif
And since .if expects a ${variable} as its first argument, it fails.
About why you need an inner loop. Remember again that .for loops
are unrolled before parsing, it means that a fragment like this:
=2Efor i in foo bar
j=3D${i}
k+=3D${j}
=2Eendfor
is equivalent to
j=3Dfoo
k+=3D${j}
j=3Dbar
k+=3D${j}
which means that `k' will get a value of "bar bar". When you use
an inner loop,
=2Efor i in foo bar
j=3D${i}
=2Efor l in ${j}
k+=3D${l}
=2Eendfor
=2Eendfor
it first gets rewritten to:
j=3Dfoo
=2Efor l in ${j}
k+=3D${l}
=2Eendfor
j=3Dbar
=2Efor l in ${j}
k+=3D${l}
=2Eendfor
then to:
j=3Dfoo
k+=3Dfoo
j=3Dbar
k+=3Dbar
which DTRT, but also has a side effect of setting "j" to "bar".
> Am I missing an easier way to do this?
>=20
May I suggest the following instead:
%%%
MANLANG?=3D foo "" bar
all:
=2Efor i in ${MANLANG:N""}
@echo foo ${i}
=2Eendfor
%%%
Note that `""' is not an empty value in make(1), it's just a
regular value consisting of two double quotes.
Cheers,
--=20
Ruslan Ermilov
ru@FreeBSD.org
FreeBSD committer
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