If your system is using pulseaudio
you could use pactl
:
pactl set-sink-volume 0 +15%
or
pactl set-sink-volume 0 -5dB
though you could also specify an integer or a linear factor:
set-sink-volume SINK VOLUME [VOLUME ...]
Set the volume of the specified sink (identified by its symbolic name or numerical index). VOLUME can be speci‐
fied as an integer (e.g. 2000, 16384), a linear factor (e.g. 0.4, 1.100), a percentage (e.g. 10%, 100%) or a
decibel value (e.g. 0dB, 20dB). If the volume specification start with a + or - the volume adjustment will be
relative to the current sink volume. A single volume value affects all channels; if multiple volume values are
given their number has to match the sink's number of channels.
amixer sget Master | grep 'Right:' | awk -F'[][]' '{ print $2 }'
Increase Master volume level by 10%:amixer -q sset Master 10%+
– Eric Leschinski Jan 21 '19 at 18:04