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Date: Wed, 25 Jan 2006 07:45:33 -0700
From: Eric Blake <ebb9@byu.net>
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Subject: Re: Shell (bash, (pd)ksh, zsh, /not/ ash) + exec + here-doc + redirect   == trouble!
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According to Eric Blake on 1/25/2006 7:41 AM:
>>>=== begin testexec.sh ===
>>>#!/bin/ksh
>>>
>>>exec 5<&0 /bin/ksh <<EOSH
>>>echo "First exec: Done."
>>>exec 0<&5
>>>echo "Second exec: Done."
>>>exit 0
>>>EOSH
>>>==== end testexec.sh ====
> 
> 
> First line: This could be rewritten "exec /bin/ksh 5<&0 <<EOSH".  Either
> way, you are replacing the current shell with an invocation of /bin/ksh,
> and with fd 5 set to your current stdin, and then with fd 0 set to a pipe
> supplied by the contents of the here-doc.

P.S. If you had written this instead:

exec /bin/ksh <<EOSH 5<&0
echo "First exec: Done."
exec 0<&5
echo "Second exec: Done."
exit 0
EOSH

then you would have the same behavior as your second example (first,
replace fd 0 with the pipe from the here-doc, then copy fd 0 to fd 5; then
in the here-doc contents, when copying 5 back to 0, you are making no
changes).  With redirections, order is important.

- --
Life is short - so eat dessert first!

Eric Blake             ebb9@byu.net
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