Re: configure scripts rely on "diff"; could use "cmp" instead if available

[Eric Blake]

[adding bug-standards]

On 05/24/2011 11:41 AM, Josh Triplett wrote:
> In trying to bootstrap a minimal environment, I ended up trying to run a
> configure script using just busybox (specifically, Debian's
> busybox-static).  This almost worked, except that the configure script
> used diff several times.  configure just uses diff for its exit code, to
> check for identical files.  The version of busybox-static in Debian
> doesn't provide diff, but does provide cmp.

That's in conflict with the current GNU Coding Standards, which states
that a program can blindly assume the existence of diff on $PATH.
Either we need to tighten GCS to forbid unqualified use of diff, or
improve the busybox setup to start providing diff as expected by GCS, or
both.

http://www.gnu.org/prep/standards/standards.html#Utilities-in-Makefiles

> Rather than unconditionally using diff, please consider detecting and
> using an appropriate $ac_files_identical program; either diff or cmp
> would work.  For that matter, such detection would also provide a good
> opportunity to check for a working diff -q or cmp -s, which run faster
> since they can stop at the first difference and don't have to generate
> output.
> 
> Does this seem like a reasonable addition to autoconf?  (If it falls
> under "OK, if someone provides a patch", I can do so.)

Certainly okay if someone provides a patch.  It's not my highest
priority, but I like the idea if it improves portability of a configure
script.

-- 
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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