If you want a likely story to explain things, then here's mine: Your colleague wanted to change an entire module definition file "in place" but didn't want to use a temporary file.

On a Unix-type command line, you can do the same thing with

But back to your script. Your colleague didn't have to slurp the file into a single variable, he or she could have read the file into an array. The amount of memory taken up would have roughly been the same and the text processing could then have been done line-by-line.

I don't know what relevant CPAN modules are out there to make in-place text file processing easier, but I'd bet there are some. For your emergency need right now the other excellent answers in this thread should give you enough to deliver something.