Bash – How to run code whenever USB device is connected

I am writing a bash script to automatically detect when my USB keyboard is plugged into my laptop (running Ubuntu 14), so I can change the keyboard layout automatically.

Here is my code so far (I got it from another post on Stack Overflow so I’m not 100% sure how it works)

#!/bin/bash
setxkbmap es
for dev in /sys/bus/usb/devices/ *-*:*
do
    if [ -f $dev/bInterfaceClass ]
    then
        if [[ "$(cat $dev/bInterfaceClass)" == "03" && "$(cat $dev/bInterfaceProtocol)" == "01" ]]
        then
            setxkbmap gb
        fi
    fi
done

I have got this to run on startup so far… But I’d like it to run every time a USB device is connected or disconnected.

It is important that I have it all run in one Bash script and not as a .rules file in …udev/… or anything. However, a single Python script will do just as well.

Answer

Thanks to ralf htp I was able to come up with the following solution. It has the following improvements:

• It is not dependent on specific keyboards, it will treat all USB keyboards in the same way.
• If the user manually switches to a different keyboard layout (one which is neither the default or the USB keyboard’s) it will not automatically switch it back to the default or USB layout.

Please feel free to improve this code at GitHub Gist

#!/bin/bash
kbd1=es #default keyboard layout
kbd2=gb #USB keyboard layout

flag=0
while true
do
    layout="$(setxkbmap -query | grep -a layout | cut -c13-14)"
    if [[ $layout == $kbd1 ]] || [[ $layout == $kbd2 ]]
    then
        for dev in /sys/bus/usb/devices*-*
        do
            if [ -f $dev/bInterfaceClass ]
            then
                if [[ "$(cat $dev/bInterfaceClass)" == "03" && "$(cat 
$dev/bInterfaceProtocol)" == "01" ]]
                then
                    if [[ "$flag" == "0" ]]
                    then
                            setxkbmap $kbd2
                    fi
                    flag=1
                    break
                fi 
                if [[ "$flag" == "1" ]]
                then
                    setxkbmap $kbd1
                fi
                flag=0
            fi
        done
    fi
    sleep 5s
done