If/Then

I tried with bash and PHP to change background color based on a numeric value in a file.
My Linux box monitors a transmiter control PC.
I use a bash script to parse a csv file and put the value of total transmitter output into a file every 10 minutes. If the value drops below 80% I want my background on web page to change color, and again change color and play a midi file if it drops below 50%. I’ve tried with bash to compare the value in file to a specific value with little luck. Also tried it with PHP with no luck. It seems like a simple task but I’m a newbie and struggling with it. Any help is appreciated.