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From: jws@hpcllf.HP.COM (John Stafford x75743)
Newsgroups: comp.unix.questions
Subject: Re: variables set in sh while loop don't get set?
Message-ID: <4210001@hpcllf.HP.COM>
Date: Mon, 28-Sep-87 20:44:08 EDT
Article-I.D.: hpcllf.4210001
Posted: Mon Sep 28 20:44:08 1987
Date-Received: Thu, 1-Oct-87 04:08:48 EDT
References: <212@ttrdd.UUCP>
Organization: Hewlett-Packard CLL
Lines: 26

Shell script loops with any I/O of the loop as a whole redirected (i.e.
stdin in your case) are run in a separate (sub-)shell process and so
changes in variables in such loops obviously are not reflected in the
parent.  Loops without redirected I/O are run in the current shell and
so changes in variables work.  This is either not documented or
obscurely documented.

I have "gotten around" this feature by writing things into temporary
files and having the parent get them from there:

   # Replace VARIABLE="" with
   temp=/tmp/x$$
   trap "rm -f $temp" 0 1 2 3 15 # Don't leave a mess
   cp /dev/null $temp            # >$temp would work also
   process | while read something
   do
      # Replace VARIABLE="$VARIABLE $something" with
      echo " $something" >>$temp
   done
   VARIABLE="`cat temp`"

It isn't perhaps the cleanest, but it works.

John Stafford -- Hewlett Packard Computer Language Lab
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