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

[Akim Demaille]

>>>>> "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?

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

Here is my proposal:

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'
+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