If you want to do some changes in order make your (huge in number of lines of code)script working(on which you recently faced some problems during extending code or adding new functionality), before incorporating the new change in the original script try to write a small script(probably a perl one liner) and check whether your that small logic will work in the small script, they try applying in the original script

I use this method if I want to include a regular expressions in to my existing scripts(huge in size), and it is assured that it works correctly provide I check it simple program or one liner.