HTML::Parser - HTML parser class |
HTML::Parser - HTML parser class
use HTML::Parser ();
# Create parser object $p = HTML::Parser->new( api_version => 3, start_h => [\&start, "tagname, attr"], end_h => [\&end, "tagname"], marked_sections => 1, );
# Parse document text chunk by chunk $p->parse($chunk1); $p->parse($chunk2); #... $p->eof; # signal end of document
# Parse directly from file $p->parse_file("foo.html"); # or open(F, "foo.html") || die; $p->parse_file(*F);
HTML::Parser version 2 style subclassing and method callbacks:
{ package MyParser; use base 'HTML::Parser';
sub start { my($self, $tagname, $attr, $attrseq, $origtext) = @_; #... }
sub end { my($self, $tagname, $origtext) = @_; #... }
sub text { my($self, $origtext, $is_cdata) = @_; #... } }
my $p = MyParser->new; $p->parse_file("foo.html");
Objects of the HTML::Parser
class will recognize markup and
separate it from plain text (alias data content) in HTML
documents. As different kinds of markup and text are recognized, the
corresponding event handlers are invoked.
HTML::Parser
in not a generic SGML parser. We have tried to
make it able to deal with the HTML that is actually ``out there'', and
it normally parses as closely as possible to the way the popular web
browsers do it instead of strictly following one of the many HTML
specifications from W3C. Where there is disagreement there is often
an option that you can enable to get the official behaviour.
The document to be parsed may be supplied in arbitrary chunks. This makes on-the-fly parsing as documents are received from the network possible.
If event driven parsing does not feel right for your application, you
might want to use HTML::TokeParser
. It is a
HTML::Parser
subclass that allows a more conventional program
structure.
The following method is used to construct a new HTML::Parser
object:
HTML::Parser
object and
returns it. Key/value pair arguments may be provided to assign event
handlers or initialize parser options. The handlers and parser
options can also be set or modified later by method calls described below.
If a top level key is in the form ``<event>_h'' (e.g., ``text_h''} then it assigns a handler to that event, otherwise it initializes a parser option. The event handler specification value must be an array reference. Multiple handlers may also be assigned with the 'handlers => [%handlers]' option. See examples below.
If new()
is called without any arguments, it will create a parser that
uses callback methods compatible with version 2 of HTML::Parser
.
See the section on ``version 2 compatibility'' below for details.
Special constructor option 'api_version => 2' can be used to initialize version 2 callbacks while still setting other options and handlers. The 'api_version => 3' option can be used if you don't want to set any options and don't want to fall back to v2 compatible mode.
Examples:
$p = HTML::Parser->new(api_version => 3, text_h => [ sub {...}, "dtext" ]);
This creates a new parser object with a text event handler subroutine that receives the original text with general entities decoded.
$p = HTML::Parser->new(api_version => 3, start_h => [ 'my_start', "self,tokens" ]);
This creates a new parser object with a start event handler method that receives the $p and the tokens array.
$p = HTML::Parser->new(api_version => 3, handlers => { text => [\@array, "event,text"], comment => [\@array, "event,text"], });
This creates a new parser object that stores the event type and the original text in @array for text and comment events.
The following methods feed the HTML document
to the HTML::Parser
object:
If an invoked event handler aborts parsing by calling $p->eof, then
$p->parse()
will return a FALSE value.
If $file contains a filename and the file can't be opened, then the method returns an undefined value and $! tells why it failed. Otherwise the return value is a reference to the parser object.
If a file handle is passed as the $file argument, then the file will normally be read until EOF, but not closed.
If an invoked event handler aborts parsing by calling $p->eof,
then $p->parse_file()
may not have read the entire file.
On systems with multi-byte line terminators, the values passed for the offset and length argspecs may be too low if parse_file is called with a file handle that is not in binary mode.
text
event if there is any remaining text).
Calling $p->eof inside a handler will terminate parsing at that point and cause $p->parse to return a FALSE value. This also terminates parsing by $p->parse_file().
The return value is a reference to the parser object.
Most parser options are controlled by boolean attributes. Each boolean attribute is enabled by calling the corresponding method with a TRUE argument and disabled with a FALSE argument. The attribute value is left unchanged if no argument is given. The return value from each method is the old attribute value.
Methods that can be used to get and/or set parser options are:
The official behaviour is enabled by enabling this attribute.
<IMG SRC=newprevlstGr.gif ALT=[PREV LIST] BORDER=0>
By default, ``LIST]'' is parsed as a boolean attribute, not as part of the ALT value as was clearly intended. This is also what Netscape sees.
The official behaviour is enabled by enabling this attribute. If enabled, it will cause the tag above to be reported as text since ``LIST]'' is not a legal attribute name.
tokens
and attr
argspecs.
tagname
and attr
argspecs,
and suppress special treatment of elements that are parsed as CDATA
for HTML.
Empty element tags look like start tags, but end with the character
sequence ``/>''. When recognized by HTML::Parser
they cause an
artificial end event in addition to the start event. The text
for
the artificial end event will be empty and the tokenpos
array will
be undefined even though the only element in the token array will have
the correct tag name.
XML processing instructions are terminated by ``?>'' instead of a simple ``>'' as is the case for HTML.
There are currently no events associated with marked section elements.
As markup and text is recognized, handlers are invoked. The following method is used to set up handlers for different events:
Event is one of text
, start
, end
, declaration
, comment
,
process
or default
.
Subroutine is a reference to a subroutine which is called to handle the event.
Method_name is the name of a method of $p which is called to handle the event.
Accum is a array that will hold the event information as sub-arrays.
If the second argument is ``'', the event is ignored. If it is undef, the default handler is invoked for the event.
Argspec is a string that describes the information to be reported
for the event. Any requested information that does not apply to a
specific event is passed as undef
. If argspec is omitted, then it
is left unchanged since last update.
The return value from $p->handle is the old callback routine or a reference to the accumulator array.
Return values from handler callback routines/methods are always
ignored. A handler callback can request parsing to be aborted by
invoking the $p->eof method. A handler callback is not allowed to
invoke $p->parse()
or $p->parse_file().
Examples:
$p->handler(start => "start", 'self, attr, attrseq, text' );
This causes the ``start'' method of object $p to be called for 'start' events. The callback signature is $p->start(\%attr, \@attr_seq, $text).
$p->handler(start => \&start, 'attr, attrseq, text' );
This causes subroutine start()
to be called for 'start' events.
The callback signature is start(\%attr, \@attr_seq, $text).
$p->handler(start => \@accum, '"S", attr, attrseq, text' );
This causes 'start' event information to be saved in @accum. The array elements will be ['S', \%attr, \@attr_seq, $text].
$p->handler(start => "");
This causes 'start' events to be ignored. It also supresses invokations of any default handler for start events. It is equivalent to $p->handler(start => sub {}), but is more efficient.
$p->handler(start => undef);
This causes no handler to be assosiated with start events. If there is a default handler it will be invoked.
Argspec is a string containing a comma separated list that describes the information reported by the event. The following argspec identifier names can be used:
self
tokens
For declaration
events, the array contains each word, comment, and
delimited string starting with the declaration type.
For comment
events, this contains each sub-comment. If
$p->strict_comments is disabled, there will be only one sub-comment.
For start
events, this contains the original tag name followed by
the attribute name/value pairs. The value of boolean attributes will
be either the value set by $p->boolean_attribute_value or the
attribute name if no value has been set by
$p->boolean_attribute_value.
For end
events, this contains the original tag name (one token
only).
For process
events, this contains the process instructions (one
token only).
tokenpos
tokens
, this array
contains two numbers. The first number is the offset of the start of
the token in the original text
and the second number is the length
of the token.
Boolean attributes in a start
event will have (0,0) for the
attribute value offset and length.
This passes undef if there are no tokens in the event (e.g., text
)
and for artifical end
events triggered by empty element tags.
If you are using these offsets and lengths to modify text
, you
should either work from right to left, or be very careful to calculate
the changes to the offsets.
token0
For declaration
events, this is the declaration type.
For start
and end
events, this is the tag name.
For process
and non-strict comment
events, this is everything
inside the tag.
This passes undef if there are no tokens in the event.
tagname
Since XML is case sensitive, the tagname case is not
changed when xml_mode
is enabled.
The declaration type of declaration elements is also passed as a tagname,
even if that is a bit strange.
In fact, in the current implementation tagname is
identical to token0
except that the name may be forced to lower case.
attr
Boolean attributes' values are either the value set by $p->boolean_attribute_value or the attribute name if no value has been set by $p->boolean_attribute_value.
This passes undef except for start
events.
Unless xml_mode
is enabled, the attribute names are forced to
lower case.
General entities are decoded in the attribute values and one layer of matching quotes enclosing the attribute values are removed.
attrseq
attr
hash in
the original sequence.
This passes undef except for start
events.
Unless xml_mode
is enabled, the attribute names are forced to lower
case.
text
dtext
script
, style
, xmp
,
and plaintext
).
The ISO 8859-1 character set (aka Latin1) is assumed for entity decoding.
It is planned that HTML::Parser
will get an utf8
option
at some point that will affect the byte sequence that characters with
codes greater than 127 will decode into.
This passes undef except for text
events.
is_cdata
script
,
style
, xmp
, and plaintext
).
When the flag is FALSE for a text event, then you should normally
either use dtext
or decode the entities yourself before the text is
processed further.
offset
length
event
The event name is one of text
, start
, end
, declaration
,
comment
, process
or default
.
line
Line causes the line number of the start of the event to be passed. The first line in the document is 1. Line counting doesn't start until at least one handler requests this value.
'...'
undef
Handlers for the following events can be registered:
text
The parser will make sure that it does not break a word or a sequence of whitespace between two text events.
start
Example:
<A HREF="http://www.perl.com/">
end
Example:
</A>
declaration
For typical HTML documents, the only declaration you are likely to find is <!DOCTYPE ...>.
Example:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html40/strict.dtd">
DTDs inside <!DOCTYPE ...> will confuse HTML::Parser.
comment
Example:
<!-- This is a comment -- -- So is this -->
process
The format and content of processing instructions is system and application dependent.
Examples:
<? HTML processing instructions > <? XML processing instructions ?>
default
When an HTML::Parser
object is constructed with no arguments, a set
of handlers is automatically provided that is compatible with the old
HTML::Parser version 2 callback methods.
This is equivalent to the following method calls:
$p->handler(start => "start", "self, tagname, attr, attrseq, text"); $p->handler(end => "end", "self, tagname, text"); $p->handler(text => "text", "self, text, is_cdata"); $p->handler(process => "process", "self, token0, text"); $p->handler(comment => sub { my($self, $tokens) = @_; for (@$tokens) {$self->comment($_);}}, "self, tokens"); $p->handler(declaration => sub { my $self = shift; $self->declaration(substr($_[0], 2, -1));}, "self, text");
Setup of these handlers can also be requested with the ``api_version => 2'' constructor option.
The HTML::Parser
class is subclassable. Parser objects are plain
hashes and HTML::Parser
reserves only hash keys that start with
``_hparser''. The parser state can be set up by invoking the init()
method which takes the same arguments as new().
The first simple example shows how you might strip out comments from an HTML document. We achieve this by setting up a comment handler that does nothing and a default handler that will print out anything else:
use HTML::Parser; HTML::Parser->new(default_h => [sub { print shift }, 'text'], comment_h => [""], )->parse_file(shift || die) || die $!;
The next example prints out the text that is inside the <title> element of an HTML document. Here we start by setting up a start handler. When it sees the title start tag it enables a text handler that prints any text found and an end handler that will terminate parsing as soon as the title end tag is seen:
use HTML::Parser ();
sub start_handler { return if shift ne "title"; my $self = shift; $self->handler(text => sub { print shift }, "dtext"); $self->handler(end => sub { shift->eof if shift eq "title"; }, "tagname,self"); }
my $p = HTML::Parser->new(api_version => 3); $p->handler( start => \&start_handler, "tagname,self"); $p->parse_file(shift || die) || die $!; print "\n";
More examples are found in the ``eg/'' directory of the HTML-Parser
distribution; the program hrefsub
shows how you can edit all links
found in a document and htextsub
how to edid the text only; the
program hstrip
shows how you can strip out certain tags/elements
and/or attributes; and the program htext
show how to obtain the
plain text, but not any script/style content.
HTML::Parser
will leave <plaintext> mode when it sees </plaintext>.
Plaintext mode should not really be escapeable.
The <style> and <script> sections do not end with the first ``</'', but need the complete corresponding end tag.
When the strict_comment option is enabled, we still recognize comments where there is something other than whitespace between even and odd ``--'' markers.
Once $p->boolean_attribute_value has been set, there is no way to restore the default behaviour.
There is currently no way to get both quote characters into the same literal argspec.
Empty tags, e.g. ``<>'' and ``</>'', are not recognized. SGML allows them to repeat the previous start tag or close the previous start tag respecitvely.
NET tags, e.g. ``code/.../'' are not recognized. This is an SGML shorthand for ``<code>...</code>''.
Unclosed start or end tags, e.g. ``<tt<b>...</b</tt>'' are not recognized.
The following messages may be produced by HTML::Parser. The notation in this listing is the same as used in the perldiag manpage:
new()
or
init()
methods.
parse()
or parse_file()
method.
This is not permitted.
marked_sections()
method was invoked in a HTML::Parser
module that was compiled without support for marked sections.
the HTML::Entities manpage, the HTML::TokeParser manpage, the HTML::HeadParser manpage, the HTML::LinkExtor manpage, the HTML::Form manpage
the HTML::TreeBuilder manpage (part of the HTML-Tree distribution)
http://www.w3.org/TR/REC-html40
More information about marked sections and processing instructions may
be found at http://www.sgml.u-net.com/book/sgml-8.htm
.
Copyright 1996-2001 Gisle Aas. All rights reserved. Copyright 1999-2000 Michael A. Chase. All rights reserved.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
HTML::Parser - HTML parser class |