bash script to control brightness/contrast

brightness_control.sh

#!/bin/bash
# brightness_control --contrast --up 10 
# brightness_control --brightness --down 5

# for the script to work without sudo, do this:
# https://frdmtoplay.com/using-ddccontrol-as-a-non-root-user/
# https://linuxconfig.org/tutorial-on-how-to-write-basic-udev-rules-in-linux

if [ "$1" = "--brightness" ]
then
	type=10
elif [ "$1" = "--contrast" ]
then
	type=12
fi

get_cmd=$(ddcutil getvcp --bus 4 "${type}")

regex="([0-9]{1,3}),"
if [[ $get_cmd =~ $regex ]]
then
    current_amount="${BASH_REMATCH[1]}"
else
    echo "$get_cmd doesn't match" >&2 
fi


if [ "$2" = "--up" ]
then
	amount=$(($current_amount+$3))
elif [ "$2" = "--down" ]
then
	amount=$(($current_amount-$3))
fi


if [ "$amount" -ge 0 -a "$amount" -le 100 ]
then
	ddcutil setvcp --bus 4 "${type}" "${amount}"
else
    echo "amount $amount is beyond range (>0,<100)" >&2 
fi


# ddcutil setvcp --bus 4 10 10
# sudo ddcutil -d 1 getvcp 0x10
# /dev/i2c-4

# CP code 0x02 (New control value             ): One or more new control values have been saved (0x02)
# VCP code 0x0b (Color temperature increment   ): 100 degree(s) Kelvin
# VCP code 0x0c (Color temperature request     ): 3000 + 100 * (feature 0B color temp increment) degree(s) Kelvin
# VCP code 0x10 (Brightness                    ): current value =    30, max value =   100
# VCP code 0x12 (Contrast                      ): current value =     0, max value =   100
# VCP code 0x14 (Select color preset           ): Setting: User 1 (0x0b)
# VCP code 0x16 (Video gain: Red               ): current value =     0, max value =   100
# VCP code 0x18 (Video gain: Green             ): current value =     0, max value =   100
# VCP code 0x1a (Video gain: Blue              ): current value =     0, max value =   100
# VCP code 0x1e (Auto setup                    ): Auto setup not active (sl=0x00)
# VCP code 0x20 (Horizontal Position (Phase)   ): current value =    50, max value =   100
# VCP code 0x30 (Vertical Position (Phase)     ): current value =    35, max value =   100
# VCP code 0x52 (Active control                ): Value: 0x00
# VCP code 0x60 (Input Source                  ): DisplayPort-1 (sl=0x0f)
# VCP code 0x62 (Audio speaker volume          ): current value =    50, max value =   100
# VCP code 0x6c (Video black level: Red        ): current value =    50, max value =   100
# VCP code 0x6e (Video black level: Green      ): current value =    50, max value =   100
# VCP code 0x70 (Video black level: Blue       ): current value =    50, max value =   100
# VCP code 0x72 (Gamma                         ): SL: 0x00 ,  SH: 0x00
# VCP code 0x73 (LUT Size                      ): Maximum retries exceeded
# VCP code 0x74 (Single point LUT operation    ): Maximum retries exceeded
# VCP code 0x75 (Block LUT operation           ): Maximum retries exceeded
# VCP code 0x78 (Display Identification Operation): Maximum retries exceeded
# VCP code 0x86 (Display Scaling               ): Max image, no aspect ration distortion (sl=0x02)
# VCP code 0x8d (Audio mute/Screen blank       ): Unmute the audio (sl=0x02), Invalid value (sh=0x00)
# VCP code 0xa4 (Window mask control           ): Maximum retries exceeded
# VCP code 0xaa (Screen Orientation            ): 0 degrees (sl=0x01)
# VCP code 0xac (Horizontal frequency          ): 26828 hz
# VCP code 0xae (Vertical frequency            ): 143.81 hz
# VCP code 0xb4 (Source Timing Mode            ): Maximum retries exceeded
# VCP code 0xb6 (Display technology type       ): LCD (active matrix) (sl=0x03)
# VCP code 0xc0 (Display usage time            ): Usage time (hours) = 498 (0x0001f2) mh=0xff, ml=0xff, sh=0x01, sl=0xf2
# VCP code 0xc3 (Transmit display descriptor   ): Maximum retries exceeded
# VCP code 0xc6 (Application enable key        ): 0x0040
# VCP code 0xc8 (Display controller type       ): Mfg: Mstar (sl=0x05), controller number: mh=0xff, ml=0x16, sh=0x00
# VCP code 0xc9 (Display firmware level        ): 0.5
# VCP code 0xca (OSD/Button Control            ): SL: 0x02 ,  SH: 0x00
# VCP code 0xcc (OSD Language                  ): English (sl=0x02)
# VCP code 0xd2 (Asset Tag                     ): Maximum retries exceeded
# VCP code 0xd6 (Power mode                    ): DPM: On,  DPMS: Off (sl=0x01)
# VCP code 0xda (Scan mode                     ): Normal operation (sl=0x00)
# VCP code 0xdc (Display Mode                  ): Invalid value (sl=0x10)
# VCP code 0xdf (VCP Version                   ): 2.2