Bash script for i3 to run a terminal in the same working directory as the current focused application

x-cwd-exec.sh

#!/usr/bin/env bash


# Based on 'i3' thread [1] and Github Gist [2]:
#   [1] https://faq.i3wm.org/question/150/how-to-launch-a-terminal-from-here/?answer=152#post-id-152 
#   [2] https://gist.github.com/viking/5851049


find_cwd_of_forground_process() {
    local pid="$1"
    local cwd

    for pid in `find_childs "$pid"`; do
        pid="`find_forground_pid "$pid"`" ||
        continue
        [ "$pid" -ne -1 ] ||
        continue
        # Use this PID if there is a working directory specified.
        [ -e "/proc/$pid/cwd" ] ||
        continue
        readlink "/proc/$pid/cwd"
        return 0
    done
    return 1
}

find_childs() {
    local pid="$1"

    pstree -lpATn "$pid" |
    grep -oP '\(\K[^)]+(?=\))'
}

find_forground_pid() {
    local pid="$1"

    ps -ho tpgid "$pid" |
    sed 's/\s//g'
}


# Get window ID.
ID="$(xdpyinfo | grep focus | cut -f4 -d " ")"
# Get PID of process whose window this is.
PID="$(xprop -id "$ID" | grep -m 1 PID | cut -d " " -f 3)"
# Get CWD of first forground process within its childs.
CWD="$(find_cwd_of_forground_process "$PID")"
if [ -n "$CWD" ]; then
    cd "$CWD"
fi &&
exec "$@"

It lasts quite long if firefox is active (with a lot of threads). Hence I ignore threads for now (option -T for pstree),