Re: autoconf test ': >emtpy' problem under Ultrix

[Jim Meyering]

Akim Demaille <address@hidden> wrote:

| >>>>> "Jim" == Jim Meyering <address@hidden> writes:
|
| Jim> I vaguely recall that we couldn't depend on touch.  However, it
| Jim> *is* in the list of programs mentioned in standards.info's
| Jim> `Utilities in Makefiles' section.
|
| Anyway, we really need to know how to create portably empty files, we
| use it at other places IIRC.
|
| Jim> | or
| Jim> |
| Jim> | cp /dev/null empty
|
| Jim> Not everyone has a /dev/null.
|
| Huh???  What for instance?

Er... Well, I guess you've caught me :-)
I can't name one offhand.  And even if I could, it probably
wouldn't be worth making a change.

Thanks :-)

| But anyway, /dev/null is *widespread* in Autoconf, so we shouldn't
| bother.

I agree. (so maybe I shouldn't have mentioned that it's not always available :-)

| Here is my proposal:

Looks good.

| Index: tests/atgeneral.m4
| ===================================================================
| RCS file: /cvs/autoconf/tests/atgeneral.m4,v
| retrieving revision 1.61
| diff -u -u -r1.61 atgeneral.m4
| --- tests/atgeneral.m4 2001/03/13 12:43:15 1.61
| +++ tests/atgeneral.m4 2001/03/19 10:11:00
| @@ -187,9 +187,16 @@
|  # Tests to run.
|  test -z "$at_tests" && at_tests=$at_tests_all
|
| +# Can we diff with `/dev/null'?  DU 5.0 refuses.
| +if diff /dev/null /dev/null >/dev/null 2>&1; then
| +  at_devnull='/dev/null'
| +else
| +  cp /dev/null at-devnull
| +  at_devnull='at-devnull'

This is just nit-picking, but...
how about factoring out that extra use of `at-devnull'
and removing all the useless single quotes?

if diff /dev/null /dev/null >/dev/null 2>&1; then
  at_devnull=/dev/null
else
  at_devnull=at-devnull
  cp /dev/null $at_devnull
fi

| +fi
| +
|  # Use `diff -u' when possible.
| -: >empty
| -if diff -u empty empty >/dev/null 2>&1; then
| +if diff $at_devnull $at_devnull >/dev/null 2>&1; then
|    at_diff='diff -u'
|  else
|    at_diff='diff'
| @@ -531,14 +538,14 @@
|          stderr, [(echo stderr:; tee stderr <at-stderr) >&5],
|          ignore, [(echo stderr:; cat at-stderr) >&5],
|          experr, [$at_diff experr at-stderr >&5 || at_failed=:],
| -        [],     [$at_diff empty  at-stderr >&5 || at_failed=:],
| +        [],     [$at_diff $at_devnull  at-stderr >&5 || at_failed=:],
|          [echo $at_n "AS_ESCAPE([$4])$at_c" | $at_diff - at-stderr >&5 || 
at_failed=:])
|  dnl Check stdout.
|  m4_case([$3],
|          stdout, [(echo stdout:; tee stdout <at-stdout) >&5],
|          ignore, [(echo stdout:; cat at-stdout) >&5],
|          expout, [$at_diff expout at-stdout >&5 || at_failed=:],
| -        [],     [$at_diff empty  at-stdout >&5 || at_failed=:],
| +        [],     [$at_diff $at_devnull  at-stdout >&5 || at_failed=:],
|          [echo $at_n "AS_ESCAPE([$3])$at_c" | $at_diff - at-stdout >&5 || 
at_failed=:])
|  dnl Check exit val.  Don't `skip' if we are precisely checking $? = 77.
|  case $at_status in