Re: piping question

[Bart Schaefer <schaefer@brasslantern.com>]

On Oct 4,  5:50pm, Christian Neukirchen wrote:
} Subject: Re: piping question
}
} Bart Schaefer <schaefer@brasslantern.com> writes:
} 
} > 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.
} 
} Unfortunately, all these hacks don't work with urxvt.  If anyone has an
} idea how to do it, I'd like to see.

This appears to be a combination of two problems:

(1) The name used by <(cat) is platform-specific.  E.g., on Debian-
    based systems, it matches /proc/self/fd/<-> which means it is
    interpreted relative to the current process, and "most" is two
    levels removed from zsh.  On some other systems it's a named
    pipe, which works independent of /proc/self/ and is why it was
    the first thing I suggested.

(2) As I feared, rxvt closes all the descriptors except 0,1,2 which
    it opened, making /proc/self/fd/<3-> all return EOF.

To avoid this, you have to hand-code /proc/$$/fd/ instead of allowing
zsh to create the /self/ name.  The exact path may vary by platform.

Also because rxvt executes the -e argument list directly rather than
going through a shell, you don't need/want to re-quote arguments, but
you also can't redirect input.

So this should do it (options to set geometry etc. may be added):

    xmost() {
      if [[ -t 0 ]]
      then
        rxvt -e most "$@"
      else
        local procself=/proc/self
        procself=${procself:A}  # Resolve symlink to actual PID
        local stdin
        exec {stdin}<&0
        rxvt -e most "$@" $procself/fd/$stdin
	exec {stdin}<&-
      fi
    }

I don't know about "most" so I didn't attempt to get the options
right, but for "less" you need to add the -f option to be able to
read the fifo.  Also note that if rxvt is put in the background,
you need to avoid closing $stdin until after it finishes, so the
best way to make this asynchronous is to add "&" after the "fi".

-- 
Barton E. Schaefer