Change screen brightness by percentage in linux systems

change_brightness

#!/bin/bash

#
# Brightness Control Script
#
# This script allows you to adjust the screen brightness on your system by
# providing a **percentage change**. It reads the current brightness level from
# /sys/class/backlight/intel_backlight/brightness, calculates the new value
# based on the percentage change, ensures it doesn't exceed the maximum
# brightness from /sys/class/backlight/intel_backlight/max_brightness, and
# updates the brightness accordingly.
#
# Usage: brightness_control [+x or -x]
#
# Example usage:
# - To increase brightness by 10%: ./brightness_control +10
# - To decrease brightness by 20%: ./brightness_control -20
#
# Author: Cesar Lara (@laraconda on github) + ChatGPT 3.5
# Date: September 12, 2023
#


# Path to brightness control files
brightness_file="/sys/class/backlight/intel_backlight/brightness"
max_brightness_file="/sys/class/backlight/intel_backlight/max_brightness"

# Read the current brightness and maximum brightness values
current_brightness=$(cat "$brightness_file")
max_brightness=$(cat "$max_brightness_file")

# Function to calculate new brightness based on percentage change
calculate_brightness() {
    local percentage_change=$1
    local new_brightness
    new_brightness=$((current_brightness + (max_brightness * percentage_change / 100)))

    # Ensure the new brightness value is within bounds
    if [ "$new_brightness" -gt "$max_brightness" ]; then
        new_brightness="$max_brightness"
    elif [ "$new_brightness" -lt 0 ]; then
        new_brightness=0
    fi

    echo "$new_brightness"
}

# Check for input argument
if [ $# -eq 1 ]; then
    percentage_change="$1"
    
    # Check if the argument starts with '+' or '-'
    if [[ "$percentage_change" == +* ]]; then
        # Increase brightness by the given percentage
        percentage_change="${percentage_change#+}"
        new_brightness=$(calculate_brightness "$percentage_change")
    elif [[ "$percentage_change" == -* ]]; then
        # Decrease brightness by the given percentage
        percentage_change="${percentage_change#-}"
        new_brightness=$(calculate_brightness "-$percentage_change")
    else
        echo "Invalid input format. Please use +x or -x to increase or decrease brightness."
        exit 1
    fi

    # Write the new brightness value
    echo "$new_brightness" > "$brightness_file"
    echo "Brightness set to $new_brightness out of $max_brightness."
else
    echo "Usage: $0 [+x or -x]"
    exit 1
fi