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Subject: Re: svn commit: r283151 - head
From: Craig Rodrigues <rodrigc@FreeBSD.org>
To: Andriy Gapon <avg@freebsd.org>
Cc: Garrett Cooper <ngie@freebsd.org>, 
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On Wed, May 20, 2015 at 10:24 AM, Andriy Gapon <avg@freebsd.org> wrote:

> >>
> >>  lib/libproc__L: \
> >> -    cddl/lib/libctf__L lib/libelf__L lib/librtld_db__L lib/libutil__L
> >> +    ${_cddl_lib_libctf} lib/libelf__L lib/librtld_db__L lib/libutil__L
>
> Should the above perhaps be ${_cddl_lib_libctf}__L?  But such that it is
> empty
> if _cddl_lib_libctf is unset.  Not sure how to express that with the make
> syntax.  In shell it'd be ${_cddl_lib_libctf:+${_cddl_lib_libctf}__L}.
>
>
You can use:

${_cddl_lib_libctf:D${_cddl_lib_libctf}__L}


If you look at the make(1) man page and look for the section
"Variable modifiers", you can see the documentation for this.

--
Craig