On Sun, Jul 03, 2005 at 09:37:49AM +0200, Gus Koppel wrote:
>
> Makefiles are not supposed to contain (or evaluate, rather)
> "`"-expressions.
Why not? Backquotes work with most shells and thus you
don't depend on GNU make.
Anyway, make never evaluates ``-expressions, see below.
I have a Makefile which bascially consists only of
PKGCONFIG = pkg-config
GTK = gtk+-2.0
LDFLAGS = `$(PKGCONFIG) $(GTK) --libs`
CFLAGS = `$(PKGCONFIG) $(GTK) --cflags`
in my experimental Gtk+ directory, so I create foo.c, run
make foo and it compiles foo with Gtk+. I could use
$(shell ...) too, but it would make no difference here.
> 'make' doesn't treat them the same way the shell does,
> i.e. expanding them. 'make' provides the "shell" function for shell
> command expansion instead. Study the 'make' documentation for further
> information about this.
Which reveals make never evaluates `` in the first place.
Backquotes have no special meaning in Makefile, make
substitutes them literally and it's the shell what
subsequently expands them. So unlike
FOO = $(echo $$RANDOM)
FOO := $(echo $$RANDOM)
where the first gives a different number each time it is
used and the second always the same (echo $$RANDOM is always
run once at the start), both
FOO = `echo $$RANDOM`
FOO := `echo $$RANDOM`
give different numbers each time they are used. Both
behaviours can be useful:
FOO = $(shell ls)
foo:
cd /tmp; echo $(FOO)
prints the contents of current directory. But
FOO = `ls`
foo:
cd /tmp; echo $(FOO)
prints the contents of /tmp -- it's the same as
foo:
cd /tmp; echo `ls`
Yeti
--
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
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