#!/bin/sh
#
# xonlargestdisplay - the geometry of the largest display minus a margin
#
# $Id$

margin=25

Die() { echo fatal error: $@ 1>&2; exit 1; }

DieIfMissing()
{
  for x in "$@"
  do
     command -v "$x" >/dev/null || Die cannot find required executable $x
  done
}

DieIfMissing sort xdisplaygeometries

xdisplaygeometries | grep -q . || Die cannot find any screens to use

xdisplaygeometries |
sort -nrtx |
head -1 |
perl -lnwe '
  my ($w,$h,$r) = /^(\d+)x(\d+)(.*)/;
  printf("%dx%d%s\n", $w-'$margin', $h-'$margin', $r)'