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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(my $fh, "<:utf8", "foo.html") || die;
$p->parse_file($fh);
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 is 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::PullParser. This is an 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 argument pairs may be provided to assign event
handlers or initialize parser options. The handlers and parser
options can also be set or modified later by the 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.
The 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.
Parsing will also abort if one of the event handlers calls $p->eof.
The effect of this is the same as:
while (1) {
my $chunk = &$code_ref();
if (!defined($chunk) || !length($chunk)) {
$p->eof;
return $p;
}
$p->parse($chunk) || return undef;
}
But it is more efficient as this loop runs internally in XS code.
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 on
a file handle that is not in binary mode.
If a filename is passed in, then parse_file() will open the file 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().
After $p->eof has been called, the parse() and parse_file() methods
can be invoked to feed new documents with the parser object.
The return value from eof() 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:
attr and @attr argspecs will have general
entities for attribute values decoded. Enabling this attribute leaves
entities alone.
tokens and attr
argspecs.
There are currently no events associated with the marked section
markup, but the text can be returned as skipped_text.
The official behaviour is enabled by enabling this attribute.
Enabling of 'strict_comment' also disables recognizing these forms as comments:
</ comment> <! comment>
The official behaviour is enabled with this attribute. If enabled, only whitespace is allowed between the tagname and the final ``>''.
<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 Mozilla 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.
Note that the offset argspec will give you the offset of the first
segment of text and length is the combined length of the segments.
Since there might be ignored tags in between, these numbers can't be
used to directly index in the original document file.
attr,
@attr and dtext should be expanded as decoded UTF-8 so they end
up compatible with the surrounding text.
If utf8_mode is enabled then it is an error to pass strings
containing characters with code above 255 to the parse() method, and
the parse() method will croak if you try.
Example: The Unicode character ``\x{2665}'' is ``\xE2\x99\xA5'' when UTF-8 encoded. The character can also be represented by the entity ``♥'' or ``♥''. If we feed the parser:
$p->parse("\xE2\x99\xA5♥");
then dtext will be reported as ``\xE2\x99\xA5\x{2665}'' without
utf8_mode enabled, but as ``\xE2\x99\xA5\xE2\x99\xA5'' when enabled.
The later string is what you want.
This option is only available with perl-5.8 or better.
tagname and attr argspecs,
and suppresses 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.
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, start_document, end_document or default.
The \&subroutine is a reference to a subroutine which is called to handle
the event.
The $method_name is the name of a method of $p which is called to handle
the event.
The @accum is an 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.
The $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.
The return value from $p->handler is the old callback routine or a reference to the accumulator array.
Any 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 the $p->parse() or $p->parse_file() method. An exception will
be raised if it tries.
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 suppresses
invocations of any default handler for start events. It is in most
cases equivalent to $p->handler(start => sub {}), but is more
efficient. It is different from the empty-sub-handler in that
skipped_text is not reset by it.
$p->handler(start => undef);
This causes no handler to be associated with start events. If there is a default handler it will be invoked.
Filters based on tags can be set up to limit the number of events reported. The main bottleneck during parsing is often the huge number of callbacks made from the parser. Applying filters can improve performance significantly.
The following methods control filters:
start event and the end event as well as any events that
would be reported in between are suppressed. The ignored elements can
contain nested occurrences of itself. Example:
$p->ignore_elements(qw(script style));
The script and style tags will always nest properly since their
content is parsed in CDATA mode. For most other tags
ignore_elements must be used with caution since HTML is often not
well formed.
start and end events involving any of the tags given are
suppressed.
start and end events involving any of the tags not given
are suppressed.
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:
attrBoolean 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 or case_sensitive 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 is removed.
The Unicode character set is assumed for entity decoding. With Perl version 5.6 or earlier only the Latin-1 range is supported, and entities for characters outside the range 0..255 are left unchanged.
@attrattr, but keys and values are passed as
individual arguments and the original sequence of the attributes is
kept. The parameters passed will be the same as the @attr calculated
here:
@attr = map { $_ => $attr->{$_} } @$attrseq;
assuming $attr and $attrseq here are the hash and array passed as the
result of attr and attrseq argspecs.
This passes no values for events besides start.
attrseqattr hash in
the original sequence.
This passes undef except for start events.
Unless xml_mode or case_sensitive is enabled, the attribute
names are forced to lower case.
columndtextscript, style,
xmp, and plaintext).
The Unicode character set is assumed for entity decoding. With Perl version 5.6 or earlier only the Latin-1 range is supported, and entities for characters outside the range 0..255 are left unchanged.
This passes undef except for text events.
eventThe event name is one of text, start, end, declaration,
comment, process, start_document or end_document.
is_cdatascript,
style, xmp, and plaintext).
if 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.
lengthlineoffsetoffset_endoffset + length.
selfAn alternative to passing self as an argspec is to register closures
that capture $self by themselves as handlers. Unfortunately this
creates circular references which prevent the HTML::Parser object
from being garbage collected. Using the self argspec avoids this
problem.
skipped_textIf an ""-handler is registered for an event, then the text for this
event is not included in skipped_text. Skipped text both before
and after the ""-event is included in the next reported
skipped_text.
tagtagname, but prefixed with ``/'' if it belongs to an end
event and ``!'' for a declaration. The tag does not have any prefix
for start events, and is in this case identical to tagname.
tagnameSince XML is case sensitive, the tagname case is not changed when
xml_mode is enabled. The same happens if the case_sensitive attribute
is set.
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.
token0For 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.
tokenpostokens, 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 artificial 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.
tokensFor 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 values 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 (always one token).
For process events, this contains the process instructions (always one
token).
textundef'...'The whole argspec string can be wrapped up in '@{...}' to signal
that the resulting event array should be flattened. This only makes a
difference if an array reference is used as the handler target.
Consider this example:
$p->handler(text => [], 'text');
$p->handler(text => [], '@{text}']);
With two text events; "foo", "bar"; then the first example will end
up with [[``foo''], [``bar'']] and the second with [``foo'', ``bar''] in
the handler target array.
Handlers for the following events can be registered:
commentExample:
<!-- This is a comment -- -- So is this -->
declarationFor 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.
defaultendExample:
</A>
end_documentprocessThe format and content of processing instructions are system and application dependent.
Examples:
<? HTML processing instructions > <? XML processing instructions ?>
startExample:
<A HREF="http://www.perl.com/";>
start_documenttextThe parser will make sure that it does not break a word or a sequence of whitespace between two text events.
The HTML::Parser can parse Unicode strings when running under
perl-5.8 or better. If Unicode is passed to $p->parse() then chunks
of Unicode will be reported to the handlers. The offset and length
argspecs will also report their position in terms of characters.
It is safe to parse raw undecoded UTF-8 if you either avoid decoding
entities and make sure to not use argspecs that do, or enable the
utf8_mode for the parser. Parsing of undecoded UTF-8 might be
useful when parsing from a file where you need the reported offsets
and lengths to match the byte offsets in the file.
If a filename is passed to $p->parse_file() then the file will be read
in binary mode. This will be fine if the file contains only ASCII or
Latin-1 characters. If the file contains UTF-8 encoded text then care
must be taken when decoding entities as described in the previous
paragraph, but better is to open the file with the UTF-8 layer so that
it is decoded properly:
open(my $fh, "<:utf8", "index.html") || die "...: $!"; $p->parse_file($fh);
If the file contains text encoded in a charset besides ASCII, Latin-1 or UTF-8 then decoding will always be needed.
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");
Setting up 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 $!;
An alternative implementation is:
use HTML::Parser;
HTML::Parser->new(end_document_h => [sub { print shift },
'skipped_text'],
comment_h => [""],
)->parse_file(shift || die) || die $!;
This will in most cases be much more efficient since only a single callback will be made.
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; the program htextsub shows how to edit 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.
You can browse the eg/ directory online from the [Browse] link on the http://search.cpan.org/~gaas/HTML-Parser/ page.
The <style> and <script> sections do not end with the first ``</'', but need the complete corresponding end tag. The standard behaviour is not really practical.
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 respectively.
NET tags, e.g. ``code/.../'' are not recognized. This is 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 result of decoding will be a mix of encoded and decoded characters for any entities that expand to characters with code above 127. This is not a good thing.
The solution is to use the Encode::encode_utf8() on the data before
feeding it to the $p->parse(). For $p->parse_file() pass a file that
has been opened in ``:utf8'' mode.
The parser can process raw undecoded UTF-8 sanely if the utf8_mode
is enabled or if the ``attr'', ``@attr'' or ``dtext'' argspecs is avoided.
the HTML::Entities manpage, the HTML::PullParser 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)
More information about marked sections and processing instructions may
be found at http://www.sgml.u-net.com/book/sgml-8.htm.
Copyright 1996-2004 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.
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HTML::Parser - HTML parser class |