The Perl Debugger Issac Goldstand Mirimar Networks

Credits / For more info  Based loosely on perldebtut  Also, don’t forget perldeb  Inside the debugger: h h or h [cmd]

Before we even get to the debugger…  Have you: Turned on warnings via use warnings or perl –w ? Do you use strict wherever possible? Does your script pass syntax checking ( perl –c )?

Example 1 – Hello World #!/usr/bin/perl $var1 = ’Hello, world!’; $var2 = “$varl\n”; print $var2;

When not to use the debugger  Not every case needs the debugger  The debugger would not have provided any significant help with the previous example  It is important to use other tools to find problems

What to use?  perl5db.pl – The command line debugger  GUI debugger – ptkdb  ActiveState – PDK, Komodo

Starting the debugger  Called by perl –d  Can be command line option: perl –d myscript.pl  …or part of the shebang line: #!/usr/bin/perl -d

The MOST IMPORTANT COMMAND ™

 q – Quits the debugger

The SECOND MOST IMPORTANT COMMAND™

 h – Displays help

The text debugger  Other common commands: v [line] – View around line (current line by default) x expr – Evaluates an expression (in list context) m expr – Shows methods that expr->can do s – Step into n – Step over c line – Set a “one time” breakpoint

Working with variables & symbols  M shows currently loaded modules + versions  S shows currently available subroutines  X / V shows variables in [current] package

Looking around  v – Shows a “block” of code, starting from current position  l – shows a single line of code, starting from current position  Either command takes an optional parameter of a line number . resets the line position to the current line

Practical use  Normal “command line” scripts  CGI scripts via –debug pragma or command arguments  mod_perl via Apache::DB  Not helpful for XSUB debugging

GUIs  ptkdb  IDEs  ActiveState PDK  I’ve personally found the PDK to be very weak (while somewhat simpler to navigate, set breakpoints, etc)

Komodo  ActiveState’s opensource-language IDE  Costs $$$  New version 3.0 just released with very complete GUI debug tools  Includes supports for watches, conditional breakpoints, immediate pane, etc  Includes support for simulating full CGI environment

The End Issac Goldstand Mirimar Networks