Bourne Shell FOR loop confusion

[Maarten Litmaath]

kevin at 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 at cs.vu.nl, mcvax!botter!maart