The problem#

Previously, I wrote a script for opening and immediately focusing xfce4-appfinder. But xfce4-appfinder will notice if it's already open and just assume you want to use the existing window. Even if it's on a different desktop. And therefore attempting to focus it will either do nothing or switch to that desktop, neither of which is desirable.

The solution#

The actual solution I settled on is more of a workaround than a solution: having xfce4-appfinder on a different desktop doesn't really make sense, so I just set it to be on all desktops (specified as the non-existent desktop -1), so it would never be on the wrong desktop:

xdotool set_desktop_for_window "$winid" -1

To actually move the window to the current desktop, replace xdotool windowactivate "$winid" with

desktop="$(xdotool get_desktop)"
win_desktop="$(xdotool get_desktop_for_window "$winid")"
if [[ "$desktop" == "$win_desktop" ]]
then
  xdotool windowactivate "$winid"
else
  xdotool set_desktop_for_window "$winid" -1
  xdotool set_desktop_for_window "$winid" "$desktop" \
          windowactivate "$winid"
fi

Although this assumes that you know the $winid of the window you want to move. If you have just the title it works just as well to use

wmctrl -R "Application Finder"

The details#

The problem#

I have my window manager set to not focus new windows because I dislike having a new window pop up while typing and having the keystrokes surprisingly sent to the new window instead of the one I thought I was typing in. While this is usually what I want, this does mean extra clicks when I did mean to open the new window.

This is particularly bad for xfce4-appfinder (or any other application launcher), since the purpose to be able to set a global keyboard shortcut like Super+Space so you can press that combination and quickly type in the application or action you want (or, even better, type just the first few characters of its name). And since it's being intentionally launched by a keyboard shortcut, there's no real concern of it grabbing keyboard focus unexpectedly.

The solution#

Put the following script in a file appfinder-and-focus.sh and set the keyboard shortcut to run it instead of just running xfce4-appfinder directly:

#!/usr/bin/bash
(xprop -spy -root _NET_CLIENT_LIST | stdbuf -oL tail -n +2 |
  while read -r line
  do
    winid="${line/#*, /}"
    if [[ $(xdotool getwindowname "$winid") == \
        "Application Finder" ]]
    then
      xdotool windowactivate "$winid"
    fi
  done) 2>/dev/null &
xfce4-appfinder &

# Wait for window to appear, then kill xprop.
xdotool search --sync --name "Application Finder" >/dev/null
pkill -P "$(jobs -p %1)"

The details#

The problem#

When writing a shell script that starts background jobs, sometimes running those jobs past the lifetime of the script doesn't make sense. (Of course, sometimes background jobs really should keeping going after the script completes, but that's not the case this post is concerned with.) In the case that either the background jobs are used to do some background computation relevant to the script or the script can conceptually be thought of as a collection of processes, it makes sense for killing the script to also kill any background jobs it started.

The solution#

At the start of the script, add

cleanup() {
    # kill all processes whose parent is this process
    pkill -P $$
}

for sig in INT QUIT HUP TERM; do
  trap "
    cleanup
    trap - $sig EXIT
    kill -s $sig "'"$$"' "$sig"
done
trap cleanup EXIT

If you really want to kill only jobs and not all child processes, use the kill_child_jobs() function from all.sh or look at the other versions in the kill-child-jobs repository.

The details#

A buggy program#

Consider the following (contrived) program¹ which starts a background process to create a file and then waits while the background process is still running before checking to see if the file exists:

#!/bin/sh

# Make sure file doesn't exist.
rm -f file

# Create file in a background process.
touch file &
# While there is a touch process running...
while ps -C "touch" > /dev/null
do
    # ... wait one second for it to complete.
    sleep 1
done
# Check if file was created.
if [ -f file ]
then
    echo "Of course it worked."
else
    echo "Huh? File wasn't created."
    # Wait for background tasks to complete.
    wait
    if [ -f file ]
    then
        echo "Now it's there!"
    else
        echo "File never created."
    fi
fi

# Clean up.
rm -f file

Naturally, it will always output "Of course it worked.", right? Run it in a terminal yourself to confirm this. But I claimed this program is buggy; there's more going on.