A small shell script that can be used on macOS to change the sound volume from the Terminal. Requires bc (should be built-in on macOS).

set_sound_volume.sh

#!/bin/bash

if [ -z "$1" -o "$1" -lt 0 -o "$1" -gt 100 ]; then
   echo "Usage: $0 new_volume" >/dev/stderr
   echo "   new_volume must be between 0 and 100" >/dev/stderr
   exit 1
fi

new_volume="$(echo "($1 * 8) / 100" | bc)"
osascript -e "tell application \"System Events\" to set volume $new_volume"; # Max is 8, min is 0