watching a logfile and doing stuff

I needed to watcha logfile and trigger an action if a specific line appeared in the logs

    #!/bin/sh

    #tail the file you want to watch

    tail -fn0 /var/log/logfile | while read line ; do

            echo "$line" | grep 'line to react to' | grep -v 'things to block the reaction' 

            if [ $? = 0 ]

            then

                    # do things

                    echo "just saw $line"

                    mpg123 triomph.mp3

            fi

    done

save this as script.sh

make it exectuable (chmod +x script.sh) 

and let it run in the background ./script.sh &