Path: utzoo!utgpu!water!watmath!clyde!cbosgd!ihnp4!laidbak!daveb
From: daveb@laidbak.UUCP (Dave Burton)
Newsgroups: comp.unix.questions
Subject: sh feature: redirection of flow control bug
Message-ID: <1316@laidbak.UUCP>
Date: 23 Jan 88 17:33:46 GMT
Reply-To: daveb@laidbak.UUCP (Dave Burton)
Organization: is pretty bad/My method of
Lines: 57

This is an ancient (but still present) bug,
so apologies if I'm reviving a dead subject.

I just had occasion to use a feature of the Bourne/Korn shells,
I/O redirection of the flow control statements. The following
script demonstrates a bug present in sh and absent in ksh:

#!/bin/sh	# replace with $WHEREEVER/bin/ksh
if [ ! -d "$1" ]
then	echo "'$1' not a dir"
	exit 1
fi >&2
cd $1
echo "hello from `pwd`"
exit 0

This fails with sh and works with ksh.
Output from the sh version:

	Script started on Sat Jan 23 11:12:34 1988
	laidbak:1% x .
	hello from /u3/daveb
	laidbak:2% x x
	'x' not a dir
	x: x: bad directory
	laidbak:3% exit
	script done on Sat Jan 23 11:12:52 1988

Output from the ksh version:
	Script started on Sat Jan 23 11:14:23 1988
	laidbak:1% x .
	hello from /u3/daveb
	laidbak:2% x x
	'x' not a dir
	laidbak:3% exit
	script done on Sat Jan 23 11:14:58 1988

I haven't tested, but I'm sure {for,while}do/done and
case/esac exhibit the same behavior as the if/fi.

The workaround is easy (if inelegant): redirect output
of each individual command; or set a flag and test it
upon completion of the if/fi.

Is there a better/preferred workaround?
The encapsulated command list is small in this
example; adding more command to the list makes
individual redirection tiresome.

Hacking the shell is out - several of the systems
this code will execute on have no source available.
And please, no sh/csh/ksh flames/merit discussions.
-- 
--------------------"Well, it looked good when I wrote it"---------------------
 Verbal: Dave Burton                        Net: ...!ihnp4!laidbak!daveb
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