Nasty bug in release 4 Bourne shell

[Andrew H. Marrinson]

In the process of porting smail3.1.19 to System V release 4, I found
a very nasty bug!  If you use exec to redirect output in a while loop
(as in ``exec >/tmp/foo'', that is an exec with no command), it only
seems to obey the first such redirection.  I RTFM and it gives me no
reason to believe this is other than a bug.  (Note: this is Bourne
shell.  I haven't checked ksh yet.)

Here is a short shell script that reproduces the behavior:

        while read b; do
        exec > $b
        cat <<EOF
        this is $b.
        EOF
        done

If you run this with the input

        file1
        file2

You get a single file, file1, containing the two lines

        this is file1.
        this is file2.

Rather than two separate files, file1 and file2, each containing their
respective single lines!

Weird, huh?

I got this result using Dell Unix.  I suspect that it is an AT&T bug,
though.  I can't imagine Dell fooled with Bourne shell at all.  Let me
know if there is a release 4 System V out there that doesn't do this!

Oh yes, Unix is a registered trademark of AT&T.  :-)
--
		Andrew H. Marrinson
		Icom Systems, Inc.
		Wheeling, IL, USA
		(andy at icom.icom.com)