On Mon, Jul 09, 2018 at 09:08:17AM -0400, Greg Wooledge wrote:
> On Sun, Jul 08, 2018 at 01:08:59PM +1000, Zenaan Harkness wrote:
> > With a bash fn like:
> > ttyGetNum () { return $(tty | grep -oE '[0-9]+$') ; }
> >
> > Then something like this will id your current tty:
> > ttyGetNum; export Xorg_vt=vt$?
>
> Ewwwww!
:D
> The return status of a shell function is NOT intended to be used this way.
> It's analogous to the exit status of a shell command. It's a single
> byte, unsigned, so you can only return 0 to 255. It's intended to convey
> success or failure, not to carry an actual data payload.
It's a byte, and I have slightly less than 255 Linux VTs, so it's
adequate to this particular purpose ;)
> I recommend that you switch to using a regular variable for this purpose.
> I happen to like "r". With a regular variable, you're not restricted to
> integers from 0 to 255, and you retain the ability to convey succss/failure
> through the return code.
>
> As an aside, you can save the call to GNU grep by simply stripping the
> leading "/dev/tty" from the output of tty using a shell parameter
> expansion:
>
> ttyGetNum() {
> local t
> t=$(tty) || return 1
> [[ $t = /dev/tty+([0-9]) ]] || return 1
> r=${t#/dev/tty}
> }
>
> if ttyGetNum; then export Xorg_vt=vt"$r"; fi
I have been on a bit of a "support dash/ posix shell" and therefore
removed various Bash-isms. There was at least one bash-ism (that I
was using) that I was not able to remove. At least not easily.
I don't remember what that was at the moment - haven't been hacking
on this for some months.
