Debugging Tools Techniques Tips – Debuggers

Here we will take a quick look at Perl Debugger. Familarity with using perl debugger is assumed.

Related Terms – Debugging Tools, Perl Debugger Breakpoint, Perl Debug Command Line, Perl Debug Module, Perl Cgi Debug

Before we even get to the debugger… Have you:

1. Turned on warnings via use warnings or perl –w?
2. Do you use strict wherever possible?
3. 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 wIt 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 Perl debugger

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

The Most Important Commands

• q – Quits the debugge
• h – Displays help

The Perl 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 wl – shows a single line of code, starting from current position wEither command takes an optional parameter of a line number
• w. 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

Perl Debugger GUIs

• ptkdb
• IDEs
• ActiveState PDK

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

Komodo Debugger

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

Reference: www.beamartyr.net/jerusalem.pm/debugger/debugger.ppt

Related Posts:

• Perl Debugging Tools – Perl Debugger Commands

Tags: Debugging Tools | Perl Cgi Debug | Perl Debug Command Line | Perl Debug Module | Perl Debugger Breakpoint

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