Is there a linux command to determine the window IDs associated with a given process ID?

xwininfo and xprop permits to retrieve what you want, but it is a little tricky.

xwininfo permits to retrieve all known windows, and xprop to query X about a single window ID for your _NET_WM_PID parameter.

So far, a hacky way to do it would be:

#!/bin/sh

findpid=$1

known_windows=$(xwininfo -root -children|sed -e 's/^ *//'|grep -E "^0x"|awk '{ print $1 }')

for id in ${known_windows}
do
    xp=$(xprop -id $id _NET_WM_PID)
    if test $? -eq 0; then
        pid=$(xprop -id $id _NET_WM_PID|cut -d'=' -f2|tr -d ' ')

        if test "x${pid}" = x${findpid}
        then
            echo "Windows Id: $id"
        fi
    fi
done

Result:

mycroft:~ $ ./find_windows.sh 1919
Windows Id: 0x1800748
Windows Id: 0x181b221
Windows Id: 0x1803ad5
Windows Id: 0x181f681
Windows Id: 0x181f658
Windows Id: 0x180006d
Windows Id: 0x1800003
Windows Id: 0x1800001
Windows Id: 0x180001e

As you will see, a single process may have a certain number of known windows, even if you see only one on your screen.

Maybe you should get these tools sources in order to make what you want.

you can look up PIDs with wmctrl too, as a matter of fact, and I think that's a better way to do it. xwininfo will return all sorts of entities which appear to be windows, but you won't really find them on your desktop.

If you do man wmctrl , you'll find that wmctrl -l lists all windows that are actually visible on your desktop with (most importantly) their window ids and titles. -p adds PIDs and -x will add window classes.

As the manual says ( RTFM, right? :D), wmctrl can also search through some of these and activate a window that matches the search. However, I have no idea what determines which one of all possible matches will be returned. On the other hand, you can use the provided listing function to write a wrapper that does the searching better and possibly based on some other properties (such as the timestamp of the last access to the window) which you can get by querying the provided win id to xprop, for example.

These lines of code below return the most recent instance a mate-terminal class window:

XTIME="_NET_WM_USER_TIME" #a shorter name for xprop query that shoul return timestamps
export TMPDIR=/dev/shm    #save tmp files to memory to make it faster
LST=`mktemp`              #tmp file to store our listing 
wmctrl -lx |  awk -F' ' '{printf("%s\t%s    \t",$1,$3); for(i=5;i<=NF;i++) printf("%s",$i); printf("\n")  }'  > $LST #pretty-print our listing of windows into the tmp file
 #To each line of listing, prepend a timestamp acquired via an xprop call
 #Use awk to find a line whose 3rd column (winclass) matches the window class "mate-terminal.Mate-terminal" and among those that do, find the one whose timestamp is the largest
while read LINE; do ID=`echo "$LINE"|cut -f 1`; TIME=`xprop -id $ID $XTIME`;  TIME="${TIME/* = /}"; echo -e "$TIME\t$LINE" ; done <$LST ) | awk -v s="mate-terminal.Mate-terminal" '$3 == s {if($1>max){max=$1;line=$0};};END{print line}'
rm $LST  #delete tmp file

Anyhow, for the thing you describe you are building—if I were you, I would find out what class of windows your desired command generates and then base my search on that, rather than on PIDs. Alternatively, you could presume that command CMD will possibly generate windows with a class name that includes CMD.

After you have found your line, you should use the window id
to activate the window via wmctrl.

Hope this helps.

A side note: I've found that xdotool can do searches based on class names and window titles too, but it is extremely slow. On my computer, this bash script (that calls quite a couple of external utilites) is 10 times as fast as the compiled alternative that is xdotool :P.

You can use:

xdotool getwindowfocus getwindowname

(As is: you don't need to replace those nice-sounding names with anything.)