/ 
HTML-SimpleParse-0.05
River stage one • 4 direct dependents • 4 total dependents
/ HTML::SimpleParse

NAME

HTML::SimpleParse - a bare-bones HTML parser

SYNOPSIS

use HTML::SimpleParse;

# Parse the text into a simple tree
my $p = new HTML::SimpleParse( $html_text );
$p->output;                 # Output the HTML verbatim

$p->text( $new_text );      # Give it some new HTML to chew on
$p->parse                   # Parse the new HTML
$p->output;

DESCRIPTION

This module is a simple HTML parser. It is similar in concept to HTML::Parser, but it differs in a couple of important ways.

First, HTML::Parser knows which tags can contain other tags, which start tags have corresponding end tags, which tags can exist only in the <HEAD> portion of the document, and so forth. HTML::SimpleParse does not know any of these things. It just finds tags and text in the HTML you give it, it does not care about the specific content of these tags (though it does distiguish between different _types_ of tags, such as comments, starting tags like <b>, ending tags like </b>, and so on).

Second, HTML::SimpleParse does not create a hierarchical tree of HTML content, but rather a simple linear list. It does not pay any attention to balancing start tags with corresponding end tags, or which pairs of tags are inside other pairs of tags.

Because of these characteristics, you can make a very effective HTML filter by sub-classing HTML::SimpleParse. For example, to remove all comments from HTML:

package NoComment;
use HTML::SimpleParse;
@ISA = qw(HTML::SimpleParse);
sub output_comment {}

package main;
NoComment->new($some_html)->output;

Methods

  • new

    $p = new HTML::SimpleParse( $some_html );

    Creates a new HTML::SimpleParse object. Optionally takes one argument, a string containing some HTML with which to initialize the object. If you give it a non-empty string, the HTML will be parsed into a tree and ready for outputting.

  • text

    $text = $p->text;
$p->text( $new_text );

    Get or set the contents of the HTML to be parsed.

  • tree

    foreach ($p->tree) { ... }

    Returns a list of all the nodes in the tree, in case you want to step through them manually or something. Each node in the tree is an anonymous hash with (at least) two data members, $node->{type} (is this a comment, a start tag, an end tag, etc.) and $node->{content} (all the text between the angle brackets, verbatim).

  • parse

    $p->parse;

    Once an object has been initialized with some text, call $p->parse and a tree will be created. After the tree is created, you can call $p->output. If you feed some text to the new() method, parse will be called automatically during your object's construction.

  • parse_args

    %hash = $p->parse_args( $arg_string );

    This routine is handy for parsing the contents of an HTML tag into key=value pairs. For instance:

    $text = 'type=checkbox checked name=flavor value="chocolate or strawberry"';
%hash = $p->parse_args( $text );
# %hash is ( type=>'checkbox', checked=>undef, name=>'flavor',
#            value=>'chocolate or strawberry' )

    Note that the position of the last m//g search on the string (the value returned by Perl's pos() function) will be altered by the parse_args function, so make sure you take that into account if (in the above example) you do $text =~ m/something/g.

    If an attribute has no value (like "checked" in the above example) then its hash value will be undefined. Check for this by using perl's exists function.

    This method actually returns a list (not a hash), so duplicate attributes and order will be preserved if you want them to be:

    @hash = $p->parse_args("name=bob name=jim value=family");

  • output

    $p->output;

    This will output the contents of the HTML, passing the real work off to the output_text, output_comment, etc. functions. If you do not override any of these methods, this module will output the exact text that it parsed into a tree in the first place.

  • get_output

    print $p->get_output

    Similar to $p->output(), but returns its result instead of printing it.

  • execute

    foreach ($p->tree) {
   print $p->execute($_);
}

    Executes a single node in the HTML parse tree. Useful if you want to loop through the nodes and output them individually.

The following methods do the actual outputting of the various parts of the HTML. Override some of them if you want to change the way the HTML is output. For instance, to strip comments from the HTML, override the output_comment method like so:

# In subclass:
sub output_comment { }  # Does nothing

  • output_text

  • output_comment

  • output_endtag

  • output_starttag

  • output_markup

  • output_ssi

CAVEATS

Please do not assume that the interface here is stable. This is a first pass, and I'm still trying to incorporate suggestions from the community. If you employ this module somewhere, make doubly sure before upgrading that none of your code breaks when you use the newer version.

BUGS

  • Embedded >s are broken

    Won't handle tags with embedded >s in them, like <input name=expr value="x > y">. This will be fixed in a future version, probably by using the parse_args method. Suggestions are welcome.

TO DO

  • extensibility

    Based on a suggestion from Randy Harmon (thanks), I'd like to make it easier for subclasses of SimpleParse to pick out other kinds of HTML blocks, i.e. extend the set {text, comment, endtag, starttag, markup, ssi} to include more members. Currently the only easy way to do that is by overriding the parse method:

    sub parse {  # In subclass
   my $self = $_[0];
   $self->SUPER::parse(@_);
   foreach ($self->tree) {
      if ($_->{content} =~ m#^a\s+#i) {
         $_->{type} = 'anchor_start';
      }
   }
}

sub output_anchor_start {
   # Whatever you want...
}

    Alternatively, this feature might be implemented by hanging attatchments onto the parsing loop, like this:

    my $parser = new SimpleParse( $html_text );
$regex = '<(a\s+.*?)>';
$parser->watch_for( 'anchor_start', $regex );

sub SimpleParse::output_anchor_start {
   # Whatever you want...
}

    I think I like that idea better. If you wanted to, you could make a subclass with output_anchor_start as one of its methods, and put the ->watch_for stuff in the constructor.

  • reading from filehandles

    It would be nice if you could initialize an object by giving it a filehandle or filename instead of the text itself.

  • tests

    I need to write a few tests that run under "make test".

AUTHOR

Ken Williams <ken@forum.swarthmore.edu>

COPYRIGHT

Copyright 1998 Swarthmore College. All rights reserved.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.