Re: [patch] "which"-builtin writes diagnostics to stdout

[Vincent Lefevre <vincent@xxxxxxxxxx>]

On 2015-09-02 09:53:17 +0100, Peter Stephenson wrote:
> On Tue, 1 Sep 2015 16:16:30 -0700
> Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx> wrote:
> > On Sep 1,  8:12am, Mikael Magnusson wrote:
> > }
> > } I guess the problem here is that in other shells, whence does not
> > } exist, and which prints 'not found' to stderr.
> > 
> > As far as I can tell, in other shells "which notacommand" prints NOTHING
> > on stdout or stderr.

The other shells (bash, dash, ksh93, mksh, posh) do not have a "which"
builtin:

  which -foo

gives the following error under GNU/Linux (Debian):

Illegal option -f
Usage: /usr/bin/which [-a] args

and I confirm that "which notacommand" prints nothing. The "which"
builtin from BusyBox v1.22.1 behaves in a similar way.

Under zsh, one can do

  alias which="whence -p"

and get the same behavior, AFAIK.

> Another sidelight on zsh's behaviour illustrating the peculiarity of
> this case...
> 
> % which true foo cat
> true: shell built-in command
> foo not found
> /bin/cat
> 
> If "foo not found" went to stderr that would make the output overall a
> bit of a mess; it's not clear there's a good argument for complicating
> it like that.  At least this looks to me like a good argument against
> changing it.

I agree. And I hardly see how the output from "which" (when it mean
"whence -c") can be useful in a script. If the user wants the pathname
to some command, he would need "whence -p".

-- 
Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)