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To: Aaron Davies <agdavi01@louisville.edu>
Cc: zsh-users@sunsite.dk
Subject: Re: Slightly OT: Error-Handling in a Pipeline, preferably non-zsh
References: <2FF1BBB1-EF20-11D8-9C9B-000A95EDC31A@louisville.edu>
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From: Philippe Troin <phil@fifi.org>
Date: 15 Aug 2004 20:03:30 -0700
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Aaron Davies <agdavi01@louisville.edu> writes:

> How do I do return-value error handling in the middle of a pipeline?
> I'd ideally like to keep this to as basic a shell level as possible,
> plain (Bourne) sh-compatible if it can be done, though a bash or zsh
> solution will be fine if not. I'm tring to write a simple script that
> will apply a command to all processes matching a name--sort of a
> generalized "killall". At the moment, it looks like this:
> 
> #!/bin/sh
> 
> name=$1
> shift
> 
> ps aux | grep $name | grep -v grep | grep -v $0 | awk '{ print $2 }' |
> xargs $@
> 
> and it works fine, and I'd like to keep it at that level of
> simplicity. The only thing is, I'd like to make it stop and return 1
> if there are no matching processes. (At the moment, it calls the
> command with an empty argument list.) The intuitive thing to do seems
> to be
> 
> ps aux | grep $name | grep -v grep | ( grep -v $0 || exit 1 ) | awk '{
> print $2 }' | xargs $@

Use your first idiom and check $pipestatus[4].

Phil.