Section 18.11. The Debugger

18.11. The Debugger

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.