sed & awk, 2nd Edition

Debugging

No aspect of programming is more frustrating or more essential than debugging. In this section, we’ll look at ways to debug awk scripts and offer advice on how to correct an awk program that fails to do what it is supposed to do.

Modern versions of awk do a pretty good job of reporting syntax errors. But even with good error detection, it is often difficult to isolate the problem. The techniques for discovering the source of the problem are a modest few and are fairly obvious. Unfortunately, most awk implementations come with no debugging tools or extensions.

There are two classes of problems with a program. The first is really a bug in the program’s logic. The program runs—that is, it finishes without reporting any error messages, but it does not produce the result you wanted. For instance, perhaps it does not create any output. This bug could be caused by failing to use a print statement to output the result of a calculation. Program errors are mental errors, if you will.

The second class of error is one in which the program fails to execute or complete execution. This could result from a syntax error and cause awk to spit code at you that it is unable to interpret. Many syntax errors are the result of a typo or a missing brace or parenthesis. Syntax errors usually generate error messages that help direct you to the problem. Sometimes, however, a program may cause awk to fail (or “core dump”) without producing any reasonable error message.^[5] This may also be caused ...