pid2xid

#!/usr/bin/env bash

#	pid2xid.sh
#	Author: William Woodruff
#	------------------------
#	Prints the X Window ID (xid) associated with a process ID.
#	Requires GNU awk.
#	------------------------
#	This code is licensed by William Woodruff under the MIT License.
#	http://opensource.org/licenses/MIT

function usage {
	echo "Usage: $(basename "${0}") <pid>"
	exit 1
}

function fatal {
	>&2 echo "Fatal: ${*}. Exiting."
	exit 2
}

function installed {
	cmd=$(command -v "${1}")

	[[ -n  "${cmd}" ]] && [[ -f "${cmd}" ]]
	return ${?}
}

function pid2xid {
	xids=($(xwininfo -int -children -root | sed -e '1,6d' | awk '{ print $1 }'))
	for xid in "${xids[@]}"; do
		[[ "${xid}" != [0-9]* ]] && continue
		pid=$(xprop -id "${xid}" _NET_WM_PID | awk '{ print $3 }')
		[[ "${pid}" != [0-9]* ]] && continue

		if [[ "${pid}" -eq "${1}" ]]; then
			echo "${xid}"
			break
		fi
	done
}

installed gawk || fatal "Missing dependency: gawk (GNU awk)."
[[ -n "${1}" && -d "/proc/${1}" ]] || usage

pid2xid "${1}"