Maximize rdesktop on startup

On my netbook, I use different displays, and I always had a difficulty when choosing the geometry option. So I wrote this as /usr/local/bin/rdesktop

#!/bin/bash

# Determine the maximum window size:
declare -i w="$(xprop -root | awk -F'[, ]' '/^_NET_WORKAREA/ { print $7 }')"
declare -i h="$(xprop -root | awk -F'[, ]' '/^_NET_WORKAREA/ { print $9 }')"
command -p rdesktop -D -g "${w}x${h}" "$@"