Bash script to open or close gnome-terminal with a single keybinding

Question

I wanted to bind a single hot key to open and close gnome-terminal in a way similar to terminal emulators such as tilda or guake. I use Ubuntu, and have configured this script to be executed when I press the key F1

The script will focus or minimize the first gnome-terminal window that is running. If no gnome-terminal is running, it will start a new one and place it in the top half of the screen.

#!/bin/bash
# Bind this script to a keyboard shortcut to add "pull-down" behaviour to
# the Gnome terminal similar to guake or tilda
# It seems to work with gnome-terminal or xfce4-terminal
# I haven't tested any other terminal emulators
TERMINAL_EMULATOR=gnome-terminal
function main {
 if [[ -z $(terminal_process) ]]; then
 # no running terminal emulator
 # open new terminal at top of the screen
 $TERMINAL_EMULATOR --geometry 80x1+0+0 &
 win_id=$(get_terminal_window)
 # set initial width to 100% and height to 45%
 xdotool windowsize $win_id $(absolute_window_size 100 45)
 xdotool windowactivate $win_id
 else 
 win_id=$(get_terminal_window)
 if [[ $(xdotool getactivewindow) == $win_id ]]; then
 # if terminal window is active, mimize
 xdotool getactivewindow windowminimize
 else
 # if terminal window is inactive, bring in focus
 xdotool windowactivate $win_id
 fi
 fi
}
function terminal_process {
 # Is gnome-terminal already running
 echo $( ps aux | grep $TERMINAL_EMULATOR | grep -v grep)
}
function get_terminal_window {
 # get id of open terminal window. Will wait for window to open if neccessary
 echo $(xdotool search --onlyvisible --sync --limit 1 --class $TERMINAL_EMULATOR)
}
function absolute_window_size {
 # convert relative window size to absolute pixel size, based on screen res
 width_percent=1ドル
 height_percent=2ドル
 IFS=x
 screen_dimensions=$(xrandr | grep connected | grep -o '[1-9]\+x[0-9]\+')
 set $screen_dimensions
 echo $(($width_percent*1ドル/100)) $(($height_percent*2ドル/100))
}
main

As someone coming from python, bash feels quite unfamiliar, and I would like some feedback on whether this script follows best practices. I also wonder if there's anything that can be simplified without losing readability.

Answer 1

Instead of this:

function terminal_process {
 # Is gnome-terminal already running
 echo $( ps aux | grep $TERMINAL_EMULATOR | grep -v grep)
}

You don't need the echo, you can let the standard output simply go through:

terminal_process() {
 # Is gnome-terminal already running
 ps aux | grep $TERMINAL_EMULATOR | grep -v grep
}

The same goes for get_terminal_window too.

Notice that I also changed the wording style of the function definition. This is the recommended style in bash, I suggest to apply this to all your functions.

---

You can actually go even further. [[ -z $(terminal_process) ]] is actually a text comparison, checking if the output of the command as a string is empty. Instead of that, it would be better to use the exit code of the function, like this:

if ! terminal_process; then
 # ...

This works, because the exit of grep will be success (= 0) if it matched something (process exists), and failure (non-zero) if it didn't match.

However, when using the function like this, since the output of grep is not captured within a $(...), it will be printed on stdout, which you probably want to avoid. You can easily suppress that by adding the -q flag:

terminal_process() {
 # Is gnome-terminal already running
 ps aux | grep $TERMINAL_EMULATOR | grep -qv grep
}

---

This can also be simplified:

echo $(($width_percent*1ドル/100)) $(($height_percent*2ドル/100))

Like this:

echo $((width_percent * 1ドル / 100)) $((height_percent * 2ドル / 100))

• Håken Lid: Will $(function_call), catch everything that goes to stdout in the function?
• janos: Yes it will. But actually I added an even better solution that doesn't need stdout at all, see my updated answer.