Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!yale!cmcl2!kramden.acf.nyu.edu!brnstnd
From: brnstnd@kramden.acf.nyu.edu (Dan Bernstein)
Newsgroups: comp.unix.shell
Subject: Re: How to pipe stderr to a command in Bourne or Korn shell
Message-ID: <14203:Oct921:04:2690@kramden.acf.nyu.edu>
Date: 9 Oct 90 21:04:26 GMT
References: <1990Oct8.204053.15797@athena.mit.edu> <5069:Oct903:10:1390@kramden.acf.nyu.edu> <39936@shemp.CS.UCLA.EDU>
Organization: IR
Lines: 20

In article <39936@shemp.CS.UCLA.EDU> das@lanai.cs.ucla.edu (David Smallberg) writes:
> In article <5069:Oct903:10:1390@kramden.acf.nyu.edu> brnstnd@kramden.acf.nyu.edu (Dan Bernstein) writes:
> >  ( exec 5>&1; exec 1>&2; exec 2>&5; foo ) | err-processor
> Unnecessary subshell creation.

[snif] I feel insulted. No, it does *not* create an extra shell. Perhaps
you should test these things before you post.

This is a good point to remember: certain builtins, such as exec,
correspond directly to system calls between fork() and exec(), and
current shells understand this perfectly.

There's also nothing wrong with using () instead of {} at the beginning
of a pipe; the shell internally surrounds each component of the pipe
with parentheses and then removes redundant levels. (Well, sort of, but
you get the idea.) In fact, {} wastes time, as it requires a semicolon
at the end---something that whoever maintains your script might later
forget.

---Dan