Start by reading perlintro. It shows the basics of reading files and using regular expressions. Write your own code. If you have specific questions, post the code you have tried, along with expected vs. actual output.

My Unix system does not have the latest modules, so I need to script everything from scratch.

You may get some ideas from Yes, even you can use CPAN so that you don't have to (poorly) re-invent some wheel. Even if you find it difficult to properly download/install modules, it may be possible is to copy-n-pasting from the source code (with the proper acknowledgements).