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

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];