change the volume of spotify from bash command line

spotify-volume.sh

#!/bin/bash
LANGUAGE="en_US"
app_name="Spotify"
current_sink_num=
sink_num_check=
app_name_check=
pactl list sink-inputs |while read line; do \
    sink_num_check=$(echo "$line" |sed -rn 's/^Sink Input #(.*)/\1/p')
    if [ "$sink_num_check" != "" ]; then
        current_sink_num="$sink_num_check"
    else
        app_name_check=$(echo "$line" \
            |sed -rn 's/application.name = "([^"]*)"/\1/p')
            if [ "$app_name_check" = "$app_name" ]; then
                pactl set-sink-input-volume "$current_sink_num" $1%
            fi
    fi
done