Bash script to adjust the volume of the currently focused window

window_volume.sh

#!/bin/bash --posix

#    Copyright (C) 2020-2023 Atrate <atrate@protonmail.com>
#
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation, either version 3 of the License, or
#    (at your option) any later version.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License
#    along with this program.  If not, see <https://www.gnu.org/licenses/>

# $1 is the variable passed to this script. It should be in the format:
# '-x%' or '+x%'. For example: '-2%' will lower the volume by 2%. with each
# execution of the script.

# Perform [[ comparisons in a case-insensitive way
# ------------------------------------------------
shopt -s nocasematch

# descendent_pids() courtesy of https://unix.stackexchange.com/a/299198
# descendent_pids() function lists all descendant process IDs of a given PID
# --------------------------------------------------------------------------
descendent_pids()
{
    # Get the child process IDs of the given process ID
    # -------------------------------------------------
    pids=$(pgrep -P "$1")
    echo "$pids"

    # For each child process, get its descendant process IDs
    # ------------------------------------------------------
    for pid in $pids;
    do
        descendent_pids "$pid"
    done
}


# For space-delimited strings, check whether they contain an exact word match
# ---------------------------------------------------------------------------
word_match()
{
    for word in $2
    do
        if [ "$word" = "$1" ]
        then
            return 0
        fi
    done
    return 1
}


# TODO: Make this nicer, maybe with an associative array?
# -------------------------------------------------------
process_paout()
{
    while read -r word
    do
        if [ -z "$papid" ]; then
            local papid=$word
        elif [ -z "$paname" ]; then
            local paname=$word
        elif [ -z "$index" ]; then
            local index=$word
        fi
        if [ -n "$index" ]; then
            if [[ "$wclass" == *"$paname"* ]] \
               || word_match "$papid" "$2"
            then
                pactl set-sink-input-volume "$index" "$1" &
                return 0
            fi
            unset index papid paname
        fi
    done <<< "$paout"

    # Return 1 if nothing has been found
    # ----------------------------------
    return 1
}


# Main program functionality
# --------------------------
main()
{
    # Get the process ID of the window that has focus and the process IDs of its
    # descendants
    # --------------------------------------------------------------------------
    wpid=$(xdotool getwindowfocus getwindowpid)
    wclass=$(xdotool getwindowfocus getwindowclassname)

    # Exit if no window is focused
    # ----------------------------
    if [ -z "$wpid" ] || [ -z "$wclass" ]
    then
        exit 1
    fi

    # Get the list of sink inputs, including their process IDs, and process names
    # and indices (serials)
    # ---------------------------------------------------------------------------
    paout=$(pactl list sink-inputs \
            | grep -e "object.serial" -e "process.id" -e "process.binary" \
            | cut -d "\"" -f2)

    # For each sink input, check if its process ID or process name is associated
    # with the focused window or its descendants if we *really* need to
    # --------------------------------------------------------------------------
    process_paout "$1" "$wpid" && exit 0
    pstree=$(echo "$wpid"; descendent_pids "$wpid")
    process_paout "$1" "$pstree" || exit 2
}

main "$@"