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Mention how to silence program probes.

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* doc/autoconf.texi (File Descriptors): Document how to silence a
program probe.

Signed-off-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Eric Blake 2010-05-11 08:00:56 -06:00
parent 5dc7189c00
commit 41a163620f
2 changed files with 18 additions and 0 deletions
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@ -1,3 +1,9 @@
2010-05-11 Eric Blake <eblake@redhat.com>
Mention how to silence program probes.
* doc/autoconf.texi (File Descriptors): Document how to silence a
program probe.
2010-04-26 Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
Error and warning message formatting cleanups.

12
doc/autoconf.texi
View File

@ -14793,6 +14793,18 @@ must be done @emph{inside} the command substitution. When running
@samp{: `cd /zorglub` 2>/dev/null} expect the error message to
escape, while @samp{: `cd /zorglub 2>/dev/null`} works properly.
On the other hand, some shells, such as Solaris or FreeBSD
@command{/bin/sh}, warn about missing programs before performing
redirections. Therefore, to silently check whether a program exists, it
is necessary to perform redirections on a subshell:
@example
$ @kbd{/bin/sh -c 'nosuch 2>/dev/null}
nosuch: not found
$ @kbd{/bin/sh -c '(nosuch) 2>/dev/null}
$ @kbd{bash -c 'nosuch 2>/dev/null'}
@end example
FreeBSD 6.2 sh may mix the trace output lines from the statements in a
shell pipeline.