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Re: How to use shell builtin command in Makefile?
From: |
Paul Smith |
Subject: |
Re: How to use shell builtin command in Makefile? |
Date: |
Wed, 22 Oct 2008 11:56:46 -0400 |
On Wed, 2008-10-22 at 09:39 -0500, Peng Yu wrote:
> BTW, what is the general rule of thumb to use := rather =? When I
> should use = rather :=?
These are described fairly well in the GNU make manual.
:= is evaluated once, when the makefile is read. = is re-evaluated
every time the variable is used.
:= is always more efficient (assuming you use the variable more than
once) and this is especially important for things like $(shell ...)
which are very expensive (comparatively); using = means that shell is
re-invoked EVERY TIME the variable is expanded in your makefile.
The downside of := is that any changes made after the line is read in
don't have any effect. So, in your case, if you use := it will only
contain the directories that existed when the makefile was read in, and
not any directories that may be created during the operation of the
makefile.
--
-------------------------------------------------------------------------------
Paul D. Smith <address@hidden> Find some GNU make tips at:
http://www.gnu.org http://make.mad-scientist.us
"Please remain calm...I may be mad, but I am a professional." --Mad Scientist
Re: How to use shell builtin command in Makefile?, Greg Chicares, 2008/10/22
Re: How to use shell builtin command in Makefile?, Paul Smith, 2008/10/22