Perl

Using Modules

• perldoc perllocal = shows what modules have been installed via cpan or manually on the current system
• get cpan if necessary and install (may also need Test::Simple and Digest::SHA to aid in downloading and checking of modules.
• sudo cpan -i Foo::Bar (get name of Foo::Bar from cpan.org)
• perldoc Foo::Bar = see user contributed perl documentation (man pages) of the module you just downloaded

Executables

• cpan
• perldoc = Look up Perl documentation in Pod format.
  • -f perlfunc = look up specific builtin functions, ex: perldoc -f sprintf

Running Perl "perlrun"

• perl -V = Summary of perl5 configuration.
• perl -d and -D = debug options

Syntax

• pass command line arguments using @ARGV, access using $ARGV[n], count with $#ARGV
• indicate end of program using the "__END__" token
• specify certain version of perl by statement "use 5.005_54;" or similar
• if( -e $file_path ) - check to see if file exists

HTML::Tree module

• my $tree = HTML::TreeBuilder->new_from_file($file_path_string);
• $tree->delete();

Traversing

• $e->tag = get element's tag name
• $e->parent = get element's parent element
• $e->attr('name') = get value of element's 'name' attribute
• $h->descendents() vs $h->lineage()
• $h->find( 'tag', ... ) = returns a list of elements at or under $h that have any of the specified tag names.
• $h->look_down( ...criteria... ) = THE BIG ONE
  • looks down at the subtree starting at the given object ($h1), looking for elements that meet criteria you provide.
  • arg list is (key, value, key, value, ...)
  • if called in scalar (or $) context, gets the first element that matches and quits
  • if called in the vector context, returns all matching elements

my @wide_pix_images = $h->look_down( "_tag", "img", "alt", "pix!", sub { $_[0]->attr(’width’) > 350 });

• • If listing more than one key/value pair, there is an implicit AND. Have to use a sub if you need an "OR" operation.

Extracting Data

• $h1->as_text = returns a string that contains all the text bits that are children (or otherwise descendants) of the given node.
• $e->content_list = an array of all the elements, text and otherwise
• $h1->as_HTML = return the current HTML element with all it descendants
• Use index notation to pull out elements that have a certain numbered position

my $col3  = ( $row2−>look−down('_tag', 'td')   )[2];

Test::More

• use Test::More;
• BEGIN: { use_ok( Some::Module ); }
• ok(expr, label_str );
• is( val1, val2, string ); isnt(...);
• like( val, qr/.../, explanation_str); unlike( ... );
• plan tests => expression evaluation to number of tests;
• skip block: SKIP: { skip( "explanation string", num_tests_in_block_to_skip ) if (expression); <some tests> }
• todo block when you know test will fail: TODO: { <test code> }
• cmp_ok( val1, operator_str, val2, test_name )
• can_ok( module or object, list of methods) ... Checks to make sure the $module or $object can do these @methods (works with functions, too).
• isa_ok() - Checks to see if the given "$object->isa($class)". Also checks to make sure the object was defined in the first place.
  • isa_ok($object, $class, $object_name);
  • isa_ok($subclass, $class, $object_name);
  • isa_ok($ref, $type, $ref_name);
• subtest - an entirely encapsulated test in itself that looks like one test to the parent script.
  • HAVE TO SPECIFY "plan tests => 56" BEFORE OR "done_testing()" AFTER OR YOUR SUBTEST WILL FAIL INEXPLICABLY.
  • THE STRING SPECIFIED AS NAME OF THE SUBTEST MUST BE ENCLOSED IN DOUBLE NOT SINGLE QUOTES, OR YOUR TEST WILL FAIL AT COMPILE TIME.

use Test::More tests => 3;

pass("First test");

subtest ’An example subtest’ => sub {
  plan tests => 2;

  pass("This is a subtest");
  pass("So is this");
};

pass("Third test");

• note( string ) - put this in the report, just like print, basically