The Perl Debugger

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The Perl Debugger

• Issac Goldstand
• isaac_at_cpan.org
• Mirimar Networks
• http//www.mirimar.net/

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Credits / For more info

• Based loosely on perldebtut
• Also, dont forget perldeb
• Inside the debugger h h or h cmd

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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)?

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Example 1 Hello World

• !/usr/bin/perl
• var1 Hello, world!
• var2 varl\n
• print var2

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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

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What to use?

• perl5db.pl The command line debugger
• GUI debugger ptkdb
• ActiveState PDK, Komodo

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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

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The MOST IMPORTANT COMMAND
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The MOST IMPORTANT COMMAND

• q Quits the debugger

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The SECOND MOST IMPORTANT COMMAND
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The SECOND MOST IMPORTANT COMMAND

• h Displays help

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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-gtcan do
• s Step into
• n Step over
• c line Set a one time breakpoint

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Working with variables symbols

• M shows currently loaded modules versions
• S shows currently available subroutines
• X / V shows variables in current package

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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

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Practical use

• Normal command line scripts
• CGI scripts via debug pragma or command
  arguments
• mod_perl via ApacheDB
• Not helpful for XSUB debugging

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GUIs

• ptkdb
• IDEs
• ActiveState PDK
• Ive personally found the PDK to be very weak
  (while somewhat simpler to navigate, set
  breakpoints, etc)

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Komodo

• ActiveStates 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

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The End
Issac Goldstand ltisaac_at_cpan.orggt Mirimar
Networks http//www.mirimar.net/