I second the recommendation for using Devel::ptkdb. What I think you are looking for, is called setting the breakpoints. As a tip, remember to save your breakpoint setup as a ptkdb file, so you don't have to reset them everytime you run the script. Numerous tutorials for ptkdb on google show how it's done. I have hardly ever used the commandline debugger, but it may have a similar breakpoint mechanism, which you can save to automatically be loaded with the file to be debugged.

Devel::ptkdb makes it as simple as clicking on a line of code, to set a breakpoint.