Perl Hacks

Chapter 6. Debugging

Hacks 51-59

Not all programs work the first time. Even if you use test-driven development and know exactly what you need to write and how to write it, you will eventually encounter code that you don't understand and which doesn't quite work right. One frequent (and frequently bad) problem-solving technique is voodoo programming, where you change a line or character here and there, hoping to stumble upon the correct incantation.

You can do better! Mastering a few Perl tricks and understanding a few tips can help you wrestle unwieldy code into submission. Amaze your coworkers. Save precious time. Find and fix failures faster! Here's how.

Hack #51. Find Compilation Errors Fast

Trace problem code as quickly as possible.

As helpful as Perl is, sometimes a missing semicolon, parenthesis, or closing quotation mark send it into a morass of confusion. Error messages clutter your logs or your console window and, try as hard as you might, you can't see what's not there or what's just a little bit wrong.

When trouble strikes, try a simple technique to zoom in on the error as quickly as possible.

The Hack

When your program really goes kablooey, the best thing to do is not to let Perl try to run it, even through your test programs. If things are going that badly wrong, take a tip from the Haskell world and convince yourself that if it at least compiles, it has to be fairly okay.^[1] Just make it compile already!

Go to the command line and tell Perl to compile the program with ...