Re: Piping stderr (was Re: Two bug reports)

["Bart Schaefer" <schaefer@xxxxxxxxxxxxxxxx>]

On Mar 23,  1:18pm, Wayne Davison wrote:
}
} I'm wondering if it would be nice to create a syntax for piping just
} stderr?

You mean, other than `2>>(...)'?

} We already have "|&" for piping both stdout and stderr

Hmm.  `|&' is short for `2>&1 |'.  What would the new syntax be short
for?  The problem being that in order to pipe "just stderr" you have
to dispose of stdout somehow.

The proposed new syntax could be short for `2>&1 >&- |' but then you
may get "bad file descriptor" because of the closed stdout.

Or it could be short for `2>&1 >/dev/null |' except that in the case
of MULTIOS that doesn't redirect stdout, it duplicates it to both
/dev/null and the pipe; we'd at the least have to document as we do
for `>&' that the effect of MULTIOS is subverted.  Plus, some platforms
don't have a /dev/null (zsh does compile for DOS, sort of).

The same problem with MULTIOS occurs with `3>&2 2>&1 1>&3 |'.

} What do you think about using "2|&"?  Or maybe "2>|&"

Of those, it'd have to be the latter, which is currently a parse error.
The issue is really one of syntactic cleanliness; `|', `&', and `|&'
are all command separators, whereas redirections such as `2>&1' are
part of the command itself.  That's why `2>&1 |' works differently
than `2>&1 >'.  The grammar gets a bit ugly if you make something that
starts with a digit into a command separator.

} Do any other shells have a syntax for this?

Not that I know of.

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com

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