#!/bin/bash
set -e

CUR="$(pactl get-sink-volume "@DEFAULT_SINK@" | awk '$1 == "Volume:" {print substr($5, 1, length($5) - 1)}')"
CUR="$((CUR - CUR % "$1"))"

case "${1:0:1}" in
    '')
        exit 1
        ;;
    '+'|'-')
        NEW="$((CUR + "$1"))"
        ;;
    *)
        NEW="$1"
        ;;
esac

[ "$NEW" -lt 0 ] && NEW=0
[ "$NEW" -gt 100 ] && NEW=100

pactl set-sink-volume "${SINK}" "$NEW"%
pactl set-sink-mute "${SINK}" 0

echo "$NEW"