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Re: Shell (bash, (pd)ksh, zsh, /not/ ash) + exec + here-doc + redirect == trouble!
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
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