BSD make -- Malformed conditional

[Matthew Seaman]

Dear all,

Posting this mostly for the archives, but it's probably relevant to some
people here too.

When hacking on Makefiles, should you wish to match an item in a list,
you might write something like this:

.for item in ${LIST}
.if ${item} == ${THING}  # Ooops!
THING_FOUND=	1
.endif
.endfor

This however is a snare and a delusion, and will lead to much weeping
and wailing, and error messages like so:

% make
"Makefile", line 7: Malformed conditional (foo == ${THING})
"Makefile", line 9: if-less endif
"Makefile", line 7: Malformed conditional (bar == ${THING})
"Makefile", line 9: if-less endif
"Makefile", line 7: Malformed conditional (baz == ${THING})
"Makefile", line 9: if-less endif
"Makefile", line 7: Malformed conditional (blurfl == ${THING})
"Makefile", line 9: if-less endif
make: fatal errors encountered -- cannot continue

Instead you should write your loops like this:

.for item in ${LIST}
.if ${THING} == ${item}
THING_FOUND=    1
.endif
.endfor

As the make(1) manual page says on the subject of string comparisons
using == or != :

     An expression may also be a numeric or string comparison: in this case,
     the left-hand side must be a variable expansion, whereas the right-hand
     side can be a constant or a variable expansion.

So it seems that despite appearing and behaving almost exactly like one,
the iterator in a .for loop is not actually a variable as such.  It also
means that to match a constant string, you can't just write:

.for item in ${LIST}
.if ${item} == "this"  # Ooops
THIS_FOUND=1
.endif
.endfor

but have to assign the text "this" to a variable somewhere, and use the
second form.

Yes, you can use ${LIST:Mthis} instead, but using this construct can be
a bit tricky in itself...

% cat Makefile

LIST=	foo bar baz blurfl

THING=	baz

all:
	@echo "OK     \$${LIST:Mfoo} = ${LIST:Mfoo}"
	@echo "Not OK \$${LIST:M\$${THING}} = ${LIST:M${THING}}"
% make
OK     ${LIST:Mfoo} = foo
Not OK ${LIST:M${THING}} = }

	Cheers,

	Matthew

-- 
Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP: http://www.infracaninophile.co.uk/pgpkey     Ramsgate
JID: matthew at infracaninophile.co.uk               Kent, CT11 9PW

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 267 bytes
Desc: OpenPGP digital signature
Url : http://lists.freebsd.org/pipermail/freebsd-ports/attachments/20120127/2011645c/signature.pgp