Set the brightness on certain Raspberry Pi compatible screens as a percentage

brightness.sh

#!/usr/bin/env bash

if ! [[ $1 =~ ^-?[0-9]+$ ]]; then
    echo "Percentage must be an integer" 1>&2
    exit 1
fi

if (( $1 < 0 || $1 > 100 )); then
    echo "Percentage value must be at least 0 or at most 100" 1>&2
    exit 1
fi

curr=`cat /sys/class/backlight/rpi_backlight/brightness`
target=`printf %.0f $(echo "$1 * 0.01 * 255" | bc)`
(( $curr > $target )) && inc=-1 || inc=1

read -d "" looper << LOOPERDEF || true
for i in \$(seq $curr $inc $target);
do
    echo \$i | tee /sys/class/backlight/rpi_backlight/brightness > /dev/null;
done
LOOPERDEF

sudo bash -c "$(echo $looper)"