This sets the volume of the default pulseaudio sink and all currently running applications to the a certain value (0-100). If you call this without a value, all applications will be reset to the volume of the default sink.

volume

#!/bin/bash

reset_volumes() {
    volume=$(pacmd dump-volumes | head -1 | sed 's/.\+: \([0-9]\+\).*real.*/\1/')
    apps=($(pacmd list-sink-inputs | grep index | cut -d " " -f 6))
    for app in $apps; do
        pacmd set-sink-input-volume ${app} ${volume}
    done
}

set_volume() {
    vol=$(( ( 65536 * $1 / 100 ) + 1 ))
    pacmd set-sink-volume 0 ${vol}
    reset_volumes
}

if [[ -n $1 ]]; then
    # WARNING: pulseaudio/pacmd has no (sensible) upper bounds for volume,
    # so if you remove the following checks, ./volume 10000 will probably
    # destroy your speakers and/or your ears.
    if (( $1 > 100 )); then
        set_volume 100
    elif (( $1 <= 0 )); then
        set_volume 0
    else
        set_volume $1
    fi
else
    reset_volumes
fi