In most cases it is silly not to use modules. If you write something yourself you are unlikey to spend more than a few hours on it, and there will be bugs. The module authors will have spend a lot of time examining and debugging the problem, and finding all the corner cases with the help of user bug reports.
If you can't compile binary modules then for CSV there is a pure perl altertanive that is slower, bu still much better tested than anything you can write.
If you Boss won't allow you to install modules then unless there is a very good reason, you should probably be looking for a new Boss.