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Date: Wed, 25 Jan 2006 10:51:55 -0500 (EST)
From: Igor Peshansky <pechtcha AT cs DOT nyu DOT edu>
Reply-To: cygwin AT cygwin DOT com
To: Eric Blake <ericblake AT comcast DOT net>
cc: cygwin AT cygwin DOT com
Subject: Re: Shell (bash, (pd)ksh, zsh, /not/ ash) + exec + here-doc + redirect  == trouble!
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On Wed, 25 Jan 2006, Eric Blake wrote:

> > You might want to quote <<'EOSH', but that's not the cause of your
> > problem.  Here's a funny thing:
> >
> > #!/bin/bash
> > exec 5<&0 /bin/bash <<'EOSH'
> > echo "First exec: Done."
> > cat
> > exec 0<&5
> > echo "Second exec: Done."
> > exit 0
> > EOSH
> >
> > works for me.  Don't ask me why, though.  Perhaps Eric will chime in.
>
> Define "works for me".
>
> $ ./exectest.sh
> First exec: Done.
> exec 0<&5
> echo "Second exec: Done."
> exit 0

D'oh!  I was thrown off by the fact that I used "bash -xv" in my test
script.  Sorry for the noise.

> Here, the cat uses fd 0 (which is still set to the pipe from the
> here-doc), and consumes it by echoing the remainder of
> the here-doc to stdout, so that when /bin/bash goes
> to read the next line, fd 0 is at EOF, and you never execute
> the "exec 0<&5" line in the shell.  Thus, the process never
> tries to duplicate fd 5 back to fd 0, and your example no longer
> hangs waiting for input from the terminal.  But it doesn't do what
> was originally intended (that is, allow /bin/bash to execute
> the remainder of the here-doc).

Right.  Your redirection order explanation is correct.
	Igor
-- 
				http://cs.nyu.edu/~pechtcha/
      |\      _,,,---,,_	    pechtcha AT cs DOT nyu DOT edu | igor AT watson DOT ibm DOT com
ZZZzz /,`.-'`'    -.  ;-;;,_		Igor Peshansky, Ph.D. (name changed!)
     |,4-  ) )-,_. ,\ (  `'-'		old name: Igor Pechtchanski
    '---''(_/--'  `-'\_) fL	a.k.a JaguaR-R-R-r-r-r-.-.-.  Meow!

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