Re: Oddity In stty

[Chris Davies <chris-usenet@roaima.co.uk>]

On Sun, 2008-08-31 at 17:35 -0400, David L. Craig wrote:
> I can't figure this out.  Why does the first pipeline suceed but the
> second fails? I'm running an up-to-date Sid.
> 
> fold -w `stty -a | head -1 | awk '{print $7}' | tr -d ';'` < /dev/null
> cat /dev/null | fold -w `stty -a | head -1 | awk '{print $7}' | tr -d ';'`
> stty: standard input: Invalid argument

It's partly because stty acts on stdin, not stdout as you might
initially expect, and partly because of the way in that the shell appears
to handle back-ticked command evaluation.

1. echo `stty -a` </dev/null

It appears that the `stty -a` is forked /before/ the </dev/null is
applied. (This may be documented; I haven't looked.)

2. cat /dev/null | echo `stty -a`

The pipe redierction appears to be applied before the `stty -a` is
processed, so that stdin is not attached to your terminal when the
stty runs.


David L. Craig <dlc.usa@comcast.net> wrote:
> Well, I figured out a way around it:  stty -a </dev/tty
> Solaris behaves similarly.  I'm surprised this isn't
> documented behavior.

The behaviour of stty /is/ documented, indirectly:

       -F, --file=DEVICE
                     open and use the specified DEVICE instead of stdin

	...

       Handle the tty line connected to standard  input. Without
       arguments, prints  baud  rate, line discipline, and deviations
       from stty sane
		       
I guess, like many man pages, you have to know what you're looking for
before you can see it.

Chris