Re: noisy gnulib-tool on IRIX

[Eric Blake]

[adding bug-autoconf for a potential optimization]

On 09/07/2010 06:14 PM, Bruno Haible wrote:
> Eric Blake wrote:
> > $ ./gnulib-tool --help 2>&1 | head -n3
> > alias: Not found
> > unalias: Not found
> > Usage: gnulib-tool --list
>
> What happens if you replace the command
>
>    unalias echo 2>/dev/null

The point is that IRIX /bin/sh lacks alias and unalias, so it treats it 
like any other command.  And in general, it does command lookup prior to 
redirections, so directly redirecting to stderr does not squelch 
messages for missing commands; hence the common idiom of first checking 
if alias/unalias exist using a subshell check, and if so then using them 
in the parent shell.

What I wasn't sure about is why you were trying to set up an alias in 
the first place, nor how you plan on working around echo(1) issues 
without the use of alias(1).

Meanwhile, in answer to your question,

$ /bin/sh -c 'alias 2>/dev/null'
alias: Not found
$ /bin/sh -c '(alias) 2>/dev/null'
$ /bin/sh -c 'exec 3>&2; exec 2>/dev/null; unalias echo; exec 2>&3; exec 
3>&-'
$

the indirect redirection of stderr prior to attempting the unfound 
command does indeed work to silence the message, without costing a 
subshell (hmm, maybe autoconf should use that trick to reduce forking at 
m4sh startup).

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