On Tue, Apr 25, 2006 at 06:56:27PM +0200, Dennis Stosberg wrote:
> [EMAIL PROTECTED] wrote:
>
> > I'd like to define a symbol ARCH in my Makefile to be the output
> > of
> > uname -m
> >
> > The obvious thing, just starting with
> >
> > ARCH = `uname -m`
> >
> > didn't seem to work. It defined ARCH to be `uname -m' instead of
> > i686 or x86_64. Not unreasonable, but What *is* the way to do
> > this?
>
> With GNU make you can use "ARCH = $(shell uname -m)".
...or even "ARCH := $(shell uname -m)", the difference being that when
you use ":=", the value will be expanded only once upon definition,
while with "=", it is evaluated anew every time you use it -- resulting
in lots of unnecessary fork()s when you have many occurrences of
$(ARCH) in your makefile.[1]
Since the result of "uname -m" is unlikely to change while running
make, this performance optimisation can safely be made.
Cheers,
Almut
[1] sceptical minds can verify this themselves: ;)
With the following little makefile
ARCH := $(shell uname -m)
target:
# $(ARCH) $(ARCH) $(ARCH) $(ARCH)
the command
$ strace -eprocess make 3>&2 2>&1 1>&3 | grep fork | wc -l
should count only 2 forks, while when using "ARCH = $(shell uname -m)"
you'd get 5 ...
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