any clues how to go about it?

I seem to be asking this follow up question a lot today: what platform are you referring to?

One way to do this on a Unix or Unix like platform you can

xtime myScript.pl
[download]

where myScript.pl is the script you are producing metrics for.

Another way you can do it that is rather crude is at the start of your script record the value of time() and at the end of the script do it again and check the difference. I've never used it, but Time::HiRes is a module you could look at for more fine toothed timing.