bash script for setting up HDMI audio on Ubuntu (based on https://wiki.archlinux.org/title/PulseAudio/Examples#HDMI_output_configuration and https://askubuntu.com/a/1415109/1606121)

hdmi.sh

#!/bin/bash

####### Constants ############

USER=$(who | grep -o "^[^ ]\+" | head -n 1)
USER_ID=$(id -u $USER)
HDMI_FLDR="/sys/class/drm/"
PULSE_SERVER="unix:/run/user/$USER_ID/pulse/native"

# Use different lock files depending on if this is run by udev or manually from the terminal
# this avoids permission issues, I think 
if [ $USER == $(whoami) ]; then
    LOCK_FILE="/tmp/hdmi_sound.lock"
else
    LOCK_FILE="/var/lock/hdmi_sound.lock"
fi

ENABLE_DESKTOP_NOTIFICATIONS=0 # Change this to a 1 to have script produce notifcations when run
NOTIFY_ICON="/usr/share/icons/gnome/256x256/status/audio-volume-high.png"
## These are needed to get the notification working
export XAUTHORITY=/home/$USER/.Xauthority
export DISPLAY=:0
export DBUS_SESSION_BUS_ADDRESS="unix:path=/run/user/$USER_ID/bus"

####### Functions ############

function alert() {
    echo $1
    if [ $ENABLE_DESKTOP_NOTIFICATIONS == 0 ]; then
	return
    fi
    if [ $USER == $(whoami) ]; then
	notify-send --icon=$NOTIFY_ICON "$1"
    else
	su $USER -c "notify-send --icon=$NOTIFY_ICON \"$1\""
    fi
}

function has_detected_hdmi_audio() {
    sudo -u $USER pactl --server $PULSE_SERVER list sinks | grep -iq -e "HDMI" -e "High Definition Audio Controller"
}

function detect_hdmi_audio() {
    readarray -t DEVICES <<< $(aplay -l | grep "card.*device.*HDMI")
    for DEVICE in "${DEVICES[@]}"; do
        CARD_STR=($(grep -o "card [0-9]\+" <<< $DEVICE))
        CARD=${CARD_STR[1]}
        DEVICE_STR=($(grep -o "device [0-9]\+" <<< $DEVICE))
        DEVICE_NUM=${DEVICE_STR[1]}
        
        echo Testing card $CARD, device $DEVICE_NUM...

        if ! $(speaker-test --channels 2 --test wav --nloops 1 --device hw:$CARD,$DEVICE_NUM | grep -qi -e left -e right); then
            continue
        fi

        echo Adding HDMI to PulseAudio...
        sudo -u $USER pactl --server $PULSE_SERVER load-module module-alsa-sink device=hw:$CARD,$DEVICE_NUM sink_name="HDMI"
        break
    done
}

function get_hdmi_sink_idx() {
    echo Searching for index of HDMI sink...
    IDX=0
    readarray -t NAMES <<< $(sudo -u $USER pactl --server $PULSE_SERVER list sinks | grep "alsa.name")
    for NAME in "${NAMES[@]}"; do
        if $(grep -qi "HDMI" <<< $NAME); then
            break
        fi
        IDX=$(( $IDX + 1 ))
    done
    if [ $IDX -ge ${#NAMES[@]} ]; then
        echo Failed to find index. Exiting
        exit
    fi
    readarray -t SINKS <<< $(sudo -u $USER pactl --server $PULSE_SERVER list sinks | grep "Sink #")
    eval "$1=$(grep -o '[0-9]\+$' <<< ${SINKS[$IDX]})"
}

function setup_hdmi_audio() {
    if ! has_detected_hdmi_audio; then
	alert "Detecting HDMI"
        echo PulseAudio has not detected any HDMI yet, so first finding device...
        detect_hdmi_audio
    fi
    get_hdmi_sink_idx IDX
    echo Switching audio to sink with index $IDX...
    sudo -u $USER pactl --server $PULSE_SERVER set-default-sink $IDX
}

#######   Script  ############

OLD_STATUS=$(cat $LOCK_FILE)
# open $LOCK_FILE (for writing/reading) and assign it file descriptor 8 (the 8 is arbitrary)
exec 8<>$LOCK_FILE
#alert "$(ls /proc/self/fd)" # check to see if fd 8 was created
# attempt to obtain an exclusive (-x) lock to file descriptor 8, and return immediately (-n) if you fail
flock -x -n 8 || exit 1
# have the lock, valid for the lifetime of the file descriptor (i.e. until the end of the script)

# This assumes there is a single HDMI port that ever gets used
for DEVICE in $(ls "$HDMI_FLDR" | grep "card*"); do
    if ! $(grep -q "HDMI" <<< "$DEVICE"); then
        continue
    fi
    STATUS_FILE="$HDMI_FLDR/$DEVICE/status"
    if ! [ -f "$STATUS_FILE" ]; then
        continue
    fi
    STATUS=$(cat "$HDMI_FLDR/$DEVICE/status")

    # flock alone didn't seem to stop multiple instances from running at once with udev
    # so also use $LOCK_FILE to keep track of the old status
    if [ $STATUS == $OLD_STATUS ]; then
	break
    else
	alert "Running custom hdmi script"
    fi
    echo $STATUS > $LOCK_FILE
    
    if [ $STATUS != "connected" ]; then
        sudo -u $USER pactl --server $PULSE_SERVER set-default-sink 1
    else
	alert "setting up HDMI"
	setup_hdmi_audio
    fi
    break
done