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From: maart@cs.vu.nl (Maarten Litmaath)
Newsgroups: comp.unix.questions
Subject: Re: Bourne Shell FOR loop confusion
Keywords: why does it do this
Message-ID: <2977@solo8.cs.vu.nl>
Date: 3 Aug 89 19:09:51 GMT
References: <689@msa3b.UUCP>
Organization: V.U. Informatica, Amsterdam, the Netherlands
Lines: 45

kevin@msa3b.UUCP (Kevin P. Kleinfelter) writes:
\...
\   for i in 1
\   do
\      read a b c
\   done < /tmp/foo
\
\If I "echo a, b, c" inside the loop, I get the expected values from the file.
\If I "echo a, b, c" after the loop, I see that they have reverted to their
\values prior to the loop.

Due to the IO redirection the `for' command is executed in a subshell... :-(

\Korn Shell has a nice way to resolve this, via an option to "read" to read
\from a specific file handle.  Bourne Shell doesn't.  I'm stuck with a system
\that does not have Korn Shell. :-(

Here's an example how to do it:

	# save old stdin and IFS
	exec 3<&0
	OIFS="$IFS"

	entry='login passwd uid gid gecos home shell'
	IFS=:
	exec 0< /etc/passwd
	eval read $entry

	# restore IFS and stdin
	IFS="$OIFS"
	exec 0<&3

	read a b c

	for i in $entry a b c
	do
		eval echo $i=\$$i
	done

In modern Bourne shells you simply use:

	read foo < bar
-- 
"Mom! Eric Newton broke the day! In 24   |Maarten Litmaath @ VU Amsterdam:
  parts!" (Mike Schmitt in misc.misc)    |maart@cs.vu.nl, mcvax!botter!maart