Bash script using dmesg to see a message on terminal when a mouse is plugged and unplugged

Question

I am trying to get my hands dirty with bash scripting and dmesg. I want to write a script which does the following :

When the mouse is plugged in, and your script is run, it will print “mouse is present” when the mouse is unplugged and the script is run, it will say “mouse is not present”.

Here is the bash script that I came up with (This is my first bash script so please go easy :P)

#!/bin/bash

touch search_file.txt
FILENAME=search_file.txt

while true
do
    dmesg -w > search_file.txt  # read for changes in the kernel ring buffer and write to a file 

    if grep -Fxqi "mouse|disconnect" "$FILENAME" # look for the keywords 
    then
        echo "Mouse is disconnected"
    else
        echo "Mouse is connected"
    fi

done

I tried running this but I don't see the desired output.

Answer 1

You specified -w option on the dmesg command, which causes the program to wait for new messages. So the first instruction in your loop never completes.

You could try this :

#!/bin/bash

touch search_file.txt
FILENAME=search_file.txt

while true
do
    dmesg > "$FILENAME"  # read for changes in the kernel ring buffer and write to a file 

    if grep -Fxqi "mouse|disconnect" "$FILENAME" # look for the keywords 
    then
        echo "Mouse is disconnected"
    else
        echo "Mouse is connected"
    fi

done