A bit more info would be helpful. Read How do I Post a Question Effectively

or

My version of the same

Your problem statement breaks down as follows from my perspective:

• Get input from user
GetOpt::Long
• Open file for reading
open

If the file is not too large, you might consider reading it into and array(ex. my @lines)

• Search for line(?s) containing user provided characters
grep might work well for you
• Do calculation on lines found
maybe write a sub-routine to do your calculations?
• Provide output to user(file, screen, web page,...?) Might want to consider this

---

... and always remember to:

use strict;
use warnings;
etc...
[download]

Hope that is helpful...