Controlling camera gain in Linux

camera_gain.sh

#!/bin/bash                                                                                                                                                                             
                                                                                                                                                                                        
if [ $# -ne 1 ]; then                                                                                                                                                                   
    echo "Usage: $0 <direction> (up/down)"                                                                                                                                              
    exit 1                                                                                                                                                                              
fi                                                                                                                                                                                      
                                                                                                                                                                                        
direction=$(echo "$1" | tr '[:upper:]' '[:lower:]')                                                                                                                                     
                                                                                                                                                                                        
current_gain=$(v4l2-ctl --get-ctrl=gain 2>/dev/null | grep -oP '[0-9]+$')                                                                                                               
                                                                                                                                                                                        
if [[ "$direction" == "up" ]]; then                                                                                                                                                     
    max_gain=$(v4l2-ctl --list-ctrls | grep 'gain' | sed -n 's/.*max=\([0-9]*\).*/\1/p')                                                                                                
    new_gain=$((current_gain + 1))                                                                                                                                                      
                                                                                                                                                                                        
    if [ "$new_gain" -gt "$max_gain" ]; then                                                                                                                                            
        exit 0                                                                                                                                                                          
    fi                                                                                                                                                                                  
                                                                                                                                                                                        
elif [[ "$direction" == "down" ]]; then                                                                                                                                                 
    min_gain=$(v4l2-ctl --list-ctrls | grep 'gain' | sed -n 's/.*min=\([0-9]*\).*/\1/p')                                                                                                
    new_gain=$((current_gain - 1))                                                                                                                                                      
                                                                                                                                                                                        
    if [ "$new_gain" -lt "$min_gain" ]; then                                                                                                                                            
        exit 0                                                                                                                                                                          
    fi                                                                                                                                                                                  
else                                                                                                                                                                                    
    echo "Invalid direction. Use 'up' or 'down'."                                                                                                                                       
    exit 2                                                                                                                                                                              
fi                                                                                                                                                                                      
                                                                                                                                                                                        
v4l2-ctl --set-ctrl=gain="$new_gain"                                                                                                                                                    
                                                  

I have to adjust gain for the webcam often, so I used some bash and Gnome hotkeys to do it right from the keyboard.

1. You have to make it executable.
2. Gnome shortcuts should use absolute paths, no ~ is allowed.

Usage:

camera_gain.sh up
camera_gain.sh down