Gnome Brightness Control Hack for fn keys

brightness.sh

#!/bin/bash
# brightness: Change all monitors brightness in software.
# by hackerb9, 2019

# Examples:  brightness 75;  brightness -5; brightness +10
# Usage:
#       brightess [n] [+n] [-n]
#       n       An integer from 0 to 100 specifies a brightness level.
#       +n      Increase brightness by n.
#       -n      Decrease brightness by n.
#               No argument shows current brightness level.

b=$(xrandr --current --verbose | grep Brightness)
b=${b#*: }                      # Remove "Brightness: "
b=${b#0.}                       # 0.30 --> 30
[[ $b == "1.0" ]] && b="100"
case $1 in
    +*|-*)
        b=$((b $1))             # b=b+10,  b=b-10
        ;;
    [0-9]*)
        b=$1                    # b=75
        ;;
    *)
        echo $b; exit
        ;;
esac

[[ $b -lt 0 ]] && b=0
[[ $b -gt 100 ]] && b=100

if [[ $b -eq 100 ]]; then
    b=1.0
else
    b=0.$b
fi

outputs=$(xrandr --current | awk '$2 == "connected" {print $1}')
for o in $outputs; do
    xrandr --output $o --brightness $b
done 

brightness_dconf.sh

#!/bin/bash
# brightness: Change all monitors brightness in software.
# by luixal (2022) based on script from hackerb9 (2019)

# Examples:  brightness 0.75;  brightness -0.5; brightness +0.1
# Usage:
#       brightess [n] [+n] [-n]
#       n       An integer from 0 to 100 specifies a brightness level.
#       +n      Increase brightness by n.
#       -n      Decrease brightness by n.
#               No argument shows current brightness level.

# get current brightness value:
b=$(dconf read /org/gnome/shell/extensions/soft-brightness/current-brightness)

# set new value according to parameter's syntax/value:
case $1 in
    +*|-*)
#        b=$((b $1))             # b=b+0.1,  b=b-0.1
        b=`echo $b $1 | bc`
        ;;
    [0-9]*)
        b=$1                    # b=0.75
        ;;
    *)
        echo $b; exit
        ;;
esac

# set min value:
[[ $(bc -l <<< "$b < 0") -eq 1 ]] && b=0
# set max value:
[[ $(bc -l <<< "$b > 1") -eq 1 ]] && b=1

# set brightness value:
dconf write /org/gnome/shell/extensions/soft-brightness/current-brightness $b

# echo current (just set) value:
echo $b

I guess this doesn't use any kind of bus so brightness change is not synced with the slider on the config popup.

Indeed, it's like another level of brightness, it taken down using this script, the slider shows it at 100% and when you move the slider it moves taking current brightness as base level. This is: if the slider is at 100% and I use this script to decrease brightness to 50%, the slider keeps showing it at 100% and if I move the slider, it decreases and increases brightness... taking that 50% level as the 100%.

Added simpler version that uses dconf instead of xrandr (seems to be the gnome way). Also, doesn't make unit conversion but takes brightness values between 0 and 1 (ej: instead of 10 you should pass 0.1).