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Unraveling Code with the Debugger

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Daniel Allen
June 05, 2006

Daniel Allen
Daniel Allen is a software developer and Linux sysadmin living in Southern Ontario. He is a founding member of Kitchener-Waterloo Perl Mongers.

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Many people who work with Perl code never touch the debugger. My goal in this article is to provide reasoned argument for adding the Perl debugger to your set of tools, as well as pointers on how to do so. Many people are most comfortable with adding debugging variables and print statements to their code. These are fine techniques; I use them too, when they are appropriate. At other times, the debugger has saved me from tearing my hair out.

To mangle an old saying, with apologies to Sartre, "Hell is other people's code." Other people think differently than I do; they use weird idioms, and sometimes their comments are incomprehensible. Invoking the debugger on someone's code is like having a conversation with the author. It opens the code to the questions I want answered, in real time--and there's another party in the conversation, the Perl interpreter. The debugger makes it easy to try things out, even quicker than writing a one-liner, because the environment's already set up for the running program.

This article is a case example of using the Perl debugger in a production environment. In this situation, we had problems with CGI scripts on a machine I don't maintain. I wanted to go in, solve the problem, and get out quickly, without unnecessarily changing anybody's code.


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