PulseAudio volume control with notifications

vol.sh

#!/usr/bin/env bash

# const
NOTIFICATION_APPNAME="vol.sh"
NOTIFICATION_ID=48741 # dice-roll randomness guaranteed

# notify title subtitle hints? icon? -> void
notify() {
	title="$1"
	subtitle="$2"
	hints="$3"
	icon="$4"

	[[ ! "$hints" ]] && hints="{}"

	gdbus call -e                                  \
		-d  org.freedesktop.Notifications          \
		-o /org/freedesktop/Notifications          \
		-m  org.freedesktop.Notifications.Notify   \
		"$NOTIFICATION_APPNAME" "$NOTIFICATION_ID" \
		"$icon" "$title" "$subtitle" "[]" "$hints" 2500 > /dev/null
}

# vol (+|-|m) -> void
vol() {
	case "$1" in
	+) pactl set-sink-volume @DEFAULT_SINK@ +2%  ;;
	-) pactl set-sink-volume @DEFAULT_SINK@ -2%  ;;
	m) pactl set-sink-mute @DEFAULT_SINK@ toggle ;;
	*) return 1 ;;
	esac
}

volume_regex="Volume: front-left: .* ([0-9]+)%.* front-right: .* ([0-9]+)%"
mute_regex="Mute: (yes|no)"

# get_vol -> muted(yes|no), left, right
get_vol() {
	pactl list sinks | while read -r line; do
		[[ "$line" =~ $mute_regex   ]] && echo -n "${BASH_REMATCH[1]} "
		[[ "$line" =~ $volume_regex ]] && {
			echo -n "${BASH_REMATCH[1]}" "${BASH_REMATCH[2]}"
			return
		}
	done
}

# vol_icon int -> string
vol_icon() {
	(( $1 > 70 )) && echo -n audio-volume-high-symbolic   && return
	(( $1 > 35 )) && echo -n audio-volume-medium-symbolic && return
	(( $1 > 10 )) && echo -n audio-volume-low-symbolic    && return

	echo -n audio-volume-muted-symbolic
}

# fatal ...args -> void
fatal() {
	echo "$@" >&2
	exit 1
}

# main -> void
main() {
	vol "$1" || fatal "Unknown arguments; use +, - or m."

	read muted left right < <(get_vol)

	title="Volume"
	description="$left%"
	(( left != right )) && description+=" / $right%"

	[[ "$muted" == yes ]] && {
		title="Muted"
		description=""
		left=0
		right=0
	}

	avg_vol=$[ (left+right) / 2 ]

	read icon < <(vol_icon "$avg_vol")
	echo "Icon: $icon"

	notify "$title" "$description" "{'value':<$avg_vol>}" "$icon"
}

main "$@"