Simple wrapper script around xrandr to easily change the display brightness

setbrightness

#!/bin/bash
# set the screen brightness on all outputs

### variables ###
# You can configure the script by editing these vars, it should not be necessary to change anything else
max="2"                                               # max allowed brightness
min="0.2"                                             # min allowed brightness (0 = blackscreen)
prefix="$(echo ${0} | rev | cut -d "/" -f 1 | rev)"   # this name is used as prefix for all output in this script
## end ##

# help text
read -r -d '' help_text <<EOF
${prefix}

a simple tool for setting the display brightness using xrandr

usage:
    ${prefix} <brightness: number/float> ARGS
args:
  -s --silent   don't output anything except errors
  -f --force    bypass checking if the submitted brightness value is allowed (validation is done anyway)
  -h --help     show this help

author: Jonas Braun <jonas.braun@jbrn.eu>
EOF

# prints the given messages with prefix
function print_messages() {
    for msg in "${@}"; do
        echo "${prefix}: ${msg}"
    done
}

# prints message(es) with prefix and exits with code 1
function print_errors_and_exit() {
    for msg in "${@}"; do
        >&2 echo "${prefix}: ${msg}"
    done
    exit 1
}

# flag defaults
force=0
silent=0

# fetch flags
for arg in ${@}; do
    [ ${arg} == "--force" ] || [ ${arg} == "-f" ] && force=1 && continue
    [ ${arg} == "--silent" ] || [ ${arg} == "-s" ] && silent=1 && continue
    [ ${arg} == "--help" ] || [ ${arg} == "-h" ] && >&2 echo "${help_text}" && exit 0
    [[ "${arg}" =~ ^[0-9]+\.?[0-9]*$ ]] && brightness=${arg} && continue

    print_errors_and_exit "Unknown argument '${arg}'. Use --help or -h for for more information."
done

# check if brightness is set
[ -z ${brightness+x} ] && print_errors_and_exit "Brightness is not specified. Use --help or -h for more information."

# don't check if brightness is too high or low if the force flag is set
if [ ${force} == 0 ]; then
  ! [ $(echo "${brightness} >= ${min}" | bc -l) == 1 ] && \
    print_errors_and_exit "The specified brightness is to low. The lowest allowed value is ${min}"
  ! [ $(echo "${max} >= ${brightness}" | bc -l) == 1 ] && \
    print_errors_and_exit "The specified brightness is to high. The highest allowed value is ${max}"
fi

#set the specified brightness for all output devices using xrandr
for display in $(xrandr -q | grep " connected" | cut -d " " -f 1); do
    xrandr --output ${display} --brightness ${brightness} && \
     [ ${silent} == 0 ] && print_messages "Brightness was set to ${brightness} for ${display}"
done