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Re: Equivalent of ksh, zsh {N}<[WORD] ?


From: Pierre Gaston
Subject: Re: Equivalent of ksh, zsh {N}<[WORD] ?
Date: Tue, 26 Aug 2008 17:41:08 +0300

On Tue, Aug 26, 2008 at 5:38 PM, R. Bernstein <address@hidden> wrote:
> Pierre Gaston writes:
>  > On Tue, Aug 26, 2008 at 4:49 PM, R. Bernstein <address@hidden> wrote:
>  > > Pierre Gaston writes:
>  > >  > On Tue, Aug 26, 2008 at 5:41 AM, R. Bernstein <address@hidden> wrote:
>  > >  > > Both zsh and ksh have a way to open a file or duplicate a file
>  > >  > > descriptor and let the interpreter pick the descriptor saving the
>  > >  > > newly-allocated file descriptor number in a variable. In particular:
>  > >  > >
>  > >  > >   exec {fd}<&0
>  > >  > >
>  > >  > > will duplicate stdin and save the newly allocated file-descriptor
>  > >  > > number to fd. Also:
>  > >  > >
>  > >  > >   exec {fd}<filename
>  > >  > >
>  > >  > > opens filename with a new file descriptor and saves the number
>  > >  > > allocated in fd. Short of going outside of the language and using
>  > >  > > lsof, /proc, or the processes table, I haven't been able to figure 
> out
>  > >  > > how to do the corresponding thing in bash. Is there a way?
>  > >  > >
>  > >  > > If not, it would be great if a future version had this extension 
> that
>  > >  > > zsh and ksh both seem to have.
>  > >  > >
>  > >  > > Thanks!
>  > >  >
>  > >  > This is a standard behaviour and you can do this in pretty much any
>  > >  > shell out there, including bash.
>  > >
>  > > Really? It doesn't seem to be documented in bashref. And when I tried 
> just
>  > > a moment ago:
>  > >
>  > >  $ {fd}<&0
>  > >  {fd}<&0
>  > >  bash: {fd}: command not found
>  > >  $ bash --version
>  > >  bash --version
>  > >  GNU bash, version 3.2.39(1)-release (i486-pc-linux-gnu)
>  > >
>  > > Perhaps you are thinking of the variation without braces?
>  > >
>  >
>  > well, I was thinking of the normal redirection syntax:
>  > exec 3<&0
>  >
>  > I doubt '{fd}<&0'  is meaningfull anywhere.....in ksh {fd} tries to
>  > run the command {fd} like in bash
>  > in zsh it tries to run the command "fd"
>  > What are you talking about???
>  >
>
> I suppose this is new enough stuff that you would need recent ksh
> or zsh version to see it. From a recent ksh 93t manual:
>
>       If one of the above, other than >&- and the ># and ># forms, is
>       preceded by ing space, then a file descriptor number > 10 will
>       be selected by the shell and stored in the variable varname.
>       If >&- or the any of the ># and ># forms is preceded by
>       {varname} the value of varname defines the file descriptor to
>       close or position.  For example:
>
>              ... 2>&1
>
>       means  file  descriptor 2 is to be opened for writing as a duplicate of
>       file descriptor 1 and
>
>              exec {n}<file
>
>      means open file named file for reading and store the file descriptor
>      number in variable n.
>
> zsh has something similar.
>
ah sorry then. I don't have ksh and zsh version recent enough




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