Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!bionet!ames!hc!lanl!beta!pt
From: pt@beta.lanl.gov (Paul A. Thiessen)
Newsgroups: comp.unix.questions
Subject: How do I detect output redirection?
Keywords: help!
Message-ID: <26942@beta.lanl.gov>
Date: 23 Jun 89 19:59:53 GMT
Distribution: usa
Organization: Los Alamos National Laboratory
Lines: 33

Okay all you UNIX hackers, answer me this. :-)

Say I have a shell command program called 'put':

for i
do
  cat $i
done

I know, it's useless. But if I say 'put * >junk', I get the
error message: 'cat: input junk is output'
  So is there any way that I can detect **before the cat statement** that
a given file is the same one that is receiving redirected output? I'd
like to have something like:

for i
do
  if (($i is not receiving stdout))
  then
    cat $i
  fi
done

Thanks for any help! Please respond via e-mail as I don't usually
read this newsgroup.

            - Paul

-- 
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PAUL THIESSEN                     (Summer only: pt@lanl.gov)
pthiessen@hmcvax.bitnet            ...uunet!jarthur!pthiesse
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