bash script linux stuff

[Nineballo]

i wanted to make a bash script that ran when i hit the brightness keys on my keyboard to lower and raise the brightness. i am new to bash scripting so try to keep it simple

 

my jank script 

                       

#!/bin/bash
var=$(cat /sys/class/backlight/intel_backlight/brightness)
echo $var
var= expr $var - 100
destdir=/sys/class/backlight/intel_backlight/brightness
sudo echo "$var" >> "$destdir".

 

i get a permissions error on the last line every time

[WereCatf]

17 minutes ago, Domi-Nate said:

sudo echo "$var" >> "$destdir".

You get a permission-error, because echo happens as root, but the redirection to the file still happens as the original user. Use

echo "$var" | sudo tee -a "$destdir"

 

[Nineballo]

now i get no permission error but it changes then reverts so nothing happens

 

nate@nate:~/Desktop$ bash brightnessup
7000
6000
7000
 

i want it to delete the number on the file and replace with the var so that the brightness goes down... what am i doing wrong

[Nineballo]

when i set 

1 hour ago, WereCatf said:

echo "$var" | sudo tee -a "$destdir"

to 

echo "4000" | sudo tee -a "$destdir"

it sets but i want the ability to have steps of 100 and every time i run it reduces the number by 100

[0x21]

#!/usr/bin/env bash

file="/sys/class/backlight/intel_backlight/brightness"

var=$(cat "$file")
var=$((var - 100))

echo "$var" |  sudo tee "$file"

 

[Nineballo]

I just wiped my computer so I could set up duel boot with kali and Ubuntu but I’m gonna mark this as solved for now...

[Nineballo]

aight ive tested it and the script works thx mshaugh