Another side effect from the entire file slurp that you had done with the code is that perl will alloc enough memory to fit the whole file into memory, and because of the way most OSs handle releasing memory back to the system you will find that your memory usage just for that portion of code is >= the largets file you act on until your perl script stops executing. This may be an issue (depending on your OS) where the system will not realize what memory is being used activly and force other applications to swap out if your memory is constrained.

-Waswas