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Fjolfrin
Asked: 2019-06-12 08:24:46 +0800 CST

Increment Brightness by value using xrandr [duplicate]

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So I have an Alienware 13 R3 with the OLED display, and for the first time I was able to change the brightness using the xrandr command. The problem was the absence of backlight in OLED displays, so I couldn't change the brightness wither with the keyboard, or in any other way. So now that I know I can change it, I want to put a key binding to change the brightness by let's say 0.1. I used this command to change the brightness:

xrandr --output eDP-1-1 --brightness .5

Does anyone know what command to use not to set the brightness, but to increase or decrease it by some value, so I can bind a macro to it. Thanks in advance!

P.S. I am completely new to Linux, so please don't go hard on me :P

xrandr laptop display brightness alienware

1 Answers

  1. Copy bash script below to a file called bright

    Then mark it executable with chmod a+x bright

    Bash Script

    #!/bin/bash

MON="DP-1-1"    # Discover monitor name with: xrandr | grep " connected"
STEP=5          # Step Up/Down brightnes by: 5 = ".05", 10 = ".10", etc.

CurrBright=$( xrandr --verbose --current | grep ^"$MON" -A5 | tail -n1 )
CurrBright="${CurrBright##* }"  # Get brightness level with decimal place

Left=${CurrBright%%"."*}        # Extract left of decimal point
Right=${CurrBright#*"."}        # Extract right of decimal point

MathBright="0"
[[ "$Left" != 0 && "$STEP" -lt 10 ]] && STEP=10     # > 1.0, only .1 works
[[ "$Left" != 0 ]] && MathBright="$Left"00          # 1.0 becomes "100"
[[ "${#Right}" -eq 1 ]] && Right="$Right"0          # 0.5 becomes "50"
MathBright=$(( MathBright + Right ))

[[ "$1" == "Up" || "$1" == "+" ]] && MathBright=$(( MathBright + STEP ))
[[ "$1" == "Down" || "$1" == "-" ]] && MathBright=$(( MathBright - STEP ))
[[ "${MathBright:0:1}" == "-" ]] && MathBright=0    # Negative not allowed
[[ "$MathBright" -gt 999  ]] && MathBright=999      # Can't go over 9.99

if [[ "${#MathBright}" -eq 3 ]] ; then
    MathBright="$MathBright"000         # Pad with lots of zeros
    CurrBright="${MathBright:0:1}.${MathBright:1:2}"
else
    MathBright="$MathBright"000         # Pad with lots of zeros
    CurrBright=".${MathBright:0:2}"
fi

xrandr --output "$MON" --brightness "$CurrBright"   # Set new brightness

# Display current brightness
printf "Monitor $MON "
echo $( xrandr --verbose --current | grep ^"$MON" -A5 | tail -n1 )
    • Change MON="DP-1-1" to your monitor name, ie MON="HDMI-1"
    • Discover your monitor names using xrandr | grep " connected"
    • Change STEP=5 to your step value, eg STEP=2 is less noticeable

    Call the script with:

    • bright Up or bright + to increase brightness by step value
    • bright Down or bright - to decrease brightness by step value
    • bright (with no parameters) to get the current brightness level

    Hopefully the bash / shell commands can easily be googled for education but if any questions don't hesitate to ask :)

    8 minutes after posting answer it occurred to me I could have used bc for floating point math and saved ~10 lines of code and the a lot of time from the 1.5 hours to write it shrugs.

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