Set displays with xrandr.
case "$display_scheme" in
"two_monitors" )
xrandr --output VGA-1 --auto --right-of VGA-0
;;
"one_monitor" )
xrandr --output VGA-1 --off
;;
"" )
printf "Display scheme is not specified.\n" >&2
exit 1
;;
* )
printf "Unrecognized display scheme '%b'.\n" "$display_scheme" >&2
exit 1
;;
esac