A wrapper is a program that internally calls another program and performs some further actions. For example, I could write a Perl script that run ls and changed the file sizes to hexadecimal.

So, based on your description, I think your program would be more like a filter than a wrapper. A filter is a program that takes the output of another program and modifies it in some way.

I suppose your script will be run either at the right side of a pipe (that is, simulator | your_script) or stand alone, in which case it would take the output from a log file or so. In any case, you'll have to read new lines as they are generated and act accordingly.

If you're at the right of a pipe, you read from STDIN as usual; if you have to work with a log, you can use File::Tail. For the XML I don't know but a search on CPAN will surely be enlightening.