Learn at least a subset of the perl debugger.
Perl's integrated debugger makes it very easy to watch your program's internal state change as it executes. At the very least, you should be familiar with the basic features summarized in Table 18-1.
Table 18-1. Debugger basics
Debugging task | Debugger command |
|---|
To run a program under the debugger | > perl -dprogram.pl |
To set a breakpoint at the current line | DB<1> b |
To set a breakpoint at line 42 | DB<1> b 42 |
To continue executing until the next break-point is reached | DB<1> c |
To continue executing until line 86 | DB<1> c 86 |
To continue executing until subroutine foo is called | DB<1>c foo |
To execute the next statement | DB<1> n |
To step into any subroutine call that's part of the next statement | DB<1> s |
To run until the current subroutine returns | DB<1> r |
To examine the contents of a variable | DB<1> x $variable |
To have the debugger watch a variable or expression, and inform you whenever it changes | DB<1>w$variable DB<1> wexpr($ess)*$ion |
To view where you are in the source code | DB<1> v |
To view line 99 of the source code | DB<1> v 99 |
To get helpful hints on the many other features of the debugger | DB<1> |h h |
The standard perldebug and perldebtut documentation provide much more detail on using the debugger. You can also download and print out a handy free summary of the most commonly used commands from http://www.perl.com/2004/11/24/debugger_ref.pdf.