piping question

piping question

[Helmut Jarausch]

Hi,

I have a command 'most' which is similar to 'less'.
Now I'd like to write a shell script 'xmost' which
should do the same as 'most' but with its output sent to a newly
generated xterm.

If I say

xterm -g 180x30+0+0  -hold -e most

I cannot pipe into it anymore, like

ls -l | xmost

Can this be achieved?

Many thanks for a hint,
Helmt.

Re: piping question

[Bart Schaefer]

On Oct 2,  4:13pm, Helmut Jarausch wrote:
}
} Now I'd like to write a shell script 'xmost' which
} should do the same as 'most' but with its output sent to a newly
} generated xterm.

xterm is going to reset the stdin/stdout of whatever command it runs
to be the terminal input/output, so you can't pipe directly into a
command that's running under xterm.

So the trick is that you have to capture the output in a file and
pass the file's name to the command running in the xterm.  Zsh will
automatically create an appropriate file name for you by using the
process substitution syntax.

So try something like this:

    xmost() {
	() { xterm -g 180x30+0+0  -hold -e "most < $1" } <(cat)
    }

If you don't have a recent zsh with anonymous functions, you'll need
a helper function of some kind to capture the file name created by
<(cat) and pass it through to xterm.

Re: piping question

[Kurtis Rader]

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As Bart pointed out xterm is going to establish a new pty via the getpty(),
posix_openpt() or equivalent API. It then attaches stdin, stdout, stderr to
that pty before launching the shell or command specified by the -e option.
By design there is no way to coerce xterm to act like a pipeline filter.

In addition to Bart's suggestion you can leverage the /proc filesystem if
you're doing this on Linux, *BSD, or other UNIX implementation that
provides it. Your xmost script can examine /proc/$$/fd/0. If it isn't
associated with a pty it can arrange for it to be the stdin of the command
running in the new xterm. Specifics are left as an exercise for the student.

On Thu, Oct 2, 2014 at 7:13 AM, Helmut Jarausch <
jarausch@igpm.rwth-aachen.de> wrote:

> Hi,
>
> I have a command 'most' which is similar to 'less'.
> Now I'd like to write a shell script 'xmost' which
> should do the same as 'most' but with its output sent to a newly
> generated xterm.
>
> If I say
>
> xterm -g 180x30+0+0  -hold -e most
>
> I cannot pipe into it anymore, like
>
> ls -l | xmost
>
> Can this be achieved?
>
> Many thanks for a hint,
> Helmt.
>



-- 
Kurtis Rader
Caretaker of the exceptional canines Junior and Hank

Re: piping question

[Mikael Magnusson]

On 2 October 2014 16:13, Helmut Jarausch <jarausch@igpm.rwth-aachen.de> wrote:
> Hi,
>
> I have a command 'most' which is similar to 'less'.
> Now I'd like to write a shell script 'xmost' which
> should do the same as 'most' but with its output sent to a newly
> generated xterm.
>
> If I say
>
> xterm -g 180x30+0+0  -hold -e most
>
> I cannot pipe into it anymore, like
>
> ls -l | xmost
>
> Can this be achieved?
>
> Many thanks for a hint,
> Helmt.

echo hi there | { xterm -e 'most <& 7' 7< <(cat) }

I forget the syntax right now for allocating an appropriate free fd,
but 7 should be free most of the time ;) It might also be possibly to
use some 7<&1 thing to avoid the extra cat, but 7<&1 isn't it.

-- 
Mikael Magnusson

Re: piping question

[Bart Schaefer]

On Oct 3, 10:55am, Helmut Jarausch wrote:
> Subject: Re: piping question
>
> On 10/03/2014 04:29:10 AM, Bart Schaefer wrote:
> > 
> >     xmost() {
> > 	() { xterm -g 180x30+0+0  -hold -e "most < $1" } <(cat)
> >     }
> > 
> 
> Many thanks, that works just fine.

For completeness:

    xmost() {
      set - "${(qq)@}"  # Requote command line arguments
      if [[ -t 0 ]]
      then
        xterm -g 180x30+0+0  -hold -e "most $*"
      else
        () { xterm -g 180x30+0+0  -hold -e "most $* < $1" } <(cat)
      fi
    }

-- 
Barton E. Schaefer

Re: piping question

[Bart Schaefer]

On Oct 3,  4:42pm, Mikael Magnusson wrote:
}
} echo hi there | { xterm -e 'most <& 7' 7< <(cat) }

I avoided that because I was concerned that some terminal emulators
would close all the descriptors above 2 when launching the command.

If it works, though, you can use the {varname}<& syntax to obtain
a free descriptor, and then you don't need <(cat).

    xmost() {
      set - "${(qq)@}"  # Requote command line arguments
      if [[ -t 0 ]]
      then
        xterm -g 180x30+0+0  -hold -e "most $*"
      else
        local stdin
        exec {stdin}<&0
        xterm -g 180x30+0+0  -hold -e "most $* <&$stdin"
      fi
    }

It's possible the [[ -t 0 ]] branch is extraneous with this trick, but
it seems prudent not to have xmost reading from two different ttys.

Re: piping question

[Bart Schaefer]

On Oct 3,  8:23am, Bart Schaefer wrote:
}
}         local stdin
}         exec {stdin}<&0
}         xterm -g 180x30+0+0  -hold -e "most $* <&$stdin"

Should probably end that with

          exec {stdin}<&-

to avoid leakage.