How can I do division with variables in a Linux shell?

Question

When I run commands in my shell as below, it returns an expr: non-integer argument error. Can someone please explain this to me?

$ x=20
$ y=5
$          


        

Answer 1

Why not use let; I find it much easier. Here's an example you may find useful:

start=`date +%s`
# ... do something that takes a while ...
sleep 71

end=`date +%s`
let deltatime=end-start
let hours=deltatime/3600
let minutes=(deltatime/60)%60
let seconds=deltatime%60
printf "Time spent: %d:%02d:%02d\n" $hours $minutes $seconds

Another simple example - calculate number of days since 1970:

let days=$(date +%s)/86400