Beefy Boxes and Bandwidth Generously Provided by pair Networks
Keep It Simple, Stupid
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??
What a terrific response! I'm glad I have enough votes today: ++ to all.

Every suggestion and opinion is valuable. When I post this as a Tutorial, I will link back to this Meditation so that all these valid discussions are available. Since I think this checklist will be most effective if I keep it as terse as possible, I have not captured all the reasons for using certain techniques in the updated meditation below. Nor have I included some of the more advanced methods mentioned.

I was most surprised at the amount of discussions surrounding Data::Dumper. I use it all the time because it always Does What I Want, probably because my programs are much simpler than those of more advanced coders. One advantage of Data::Dumper over its CPAN counterparts is that it is a core module, and therefore, no installation is required. Since this checklist will be geared for beginners, I will mention Data::Dumper and acknowledge the more advanced alternatives. And I will stop being so lazy and try some of them myself to see what I'm missing!

Rather than cluttering the Monastery with individual replies to all your replies, I will toss bouquets of "Thank You"'s to all who spent their time to remind me of and teach me new techniques:

my @righteous_monks= qw( GrandFather tye YourMother kyle Tanktalus JavaFan jplindstrom rcaputo roho bart ELISHEVA tilly gwadej # from the CB );

Are you new to Perl? Is your program misbehaving? Not sure where or how to begin debugging? Well, here is a concise checklist of tips and techniques to get you started.

This list is meant for debugging some of the most common Perl programming problems; it assumes no prior working experience with the Perl debugger (perldebtut). Think of it as a First Aid kit, rather than a fully-staffed state-of-the-art operating room.

These tips are meant to act as a guide to help you answer the following questions:

  • Are you sure your data is what you think it is?
  • Are you sure your code is what you think it is?
  • Are you inadvertently ignoring error and warning messages?
  1. Add the "stricture" pragmas (Use strict and warnings)
  2. use strict; use warnings; use diagnostics;
  3. Display the contents of variables using print or warn
  4. warn "$var\n"; print "@things\n"; # array with spaces between elements
  5. Check for unexpected whitespace
    • chomp, then print with delimiters of your choice, such as colons or balanced brackets, for visibility
      chomp $var; print ">>>$var<<<\n";
    • Check for unprintable characters by converting them into their ASCII hex codes using ord
      my $copy = $str; $copy =~ s/([^\x20-\x7E])/sprintf '\x{%02x}', ord $1/eg; print ":$copy:\n";
  6. Dump arrays, hashes and arbitrarily complex data structures. You can get started using the core module Data::Dumper. Should the output prove to be unsuitable to you, other alternatives can be downloaded from CPAN, such as Data::Dump, YAML, or JSON. See also How can I visualize my complex data structure?
  7. use Data::Dumper; print Dumper(\%hash); print Dumper($ref);
  8. If you were expecting a reference, make sure it is the right kind (ARRAY, HASH, etc.)
  9. print ref $ref, "\n";
  10. Check to see if your code is what you thought it was: B::Deparse

  11. $ perl -MO=Deparse -p program.pl
  12. Check the return (error) status of your commands

    • open with $!
      open my $fh, '<', 'foo.txt' or die "can not open foo.txt: $!";
    • system and backticks (qx) with $?
      if (system $cmd) { print "Error: $? for command $cmd" } else { print "Command $cmd is OK" } $out = `$cmd`; print $? if $?;
    • eval with $@
      eval { do_something() }; warn $@ if $@;
  13. Use Carp to display variables with a stack trace of module names and function calls.
  14. use Carp qw(cluck); cluck "var is ($var)";
  15. Demystify regular expressions by installing and using the CPAN module YAPE::Regex::Explain
  16. # what the heck does /^\s+$/ mean? use YAPE::Regex::Explain; print YAPE::Regex::Explain->new('/^\s+$/')->explain();
  17. Neaten up your code by installing and using perltidy (see also the CPAN module Perl::Tidy). Poor indentation can often obscure problems.
  18. Checklist for debugging when using CPAN modules:
    • Check the Bug List by following the module's "View Bugs" link.
    • Is your installed version the latest version? If not, check the change log by following the "Changes" link.
    • If a module provides status methods, check them in your code as you would check return status of built-in functions:
      use WWW::Mechanize; if ($mech->success()) { ... }
What's next? If you are not already doing so, use an editor that understands Perl syntax (such as vim or emacs), a GUI debugger (such as Devel::ptkdb) or use a full-blown IDE. Lastly, use a version control system so that you can fearlessly make these temporary hacks to your code without trashing the real thing.

In reply to Re: RFC: Basic debugging checklist (updated) by toolic
in thread RFC: Basic debugging checklist by toolic

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • Outside of code tags, you may need to use entities for some characters:
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others lurking in the Monastery: (9)
    As of 2014-10-21 22:52 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      For retirement, I am banking on:










      Results (112 votes), past polls