parser(3)

NAME

HTML::Parser - HTML parser class

SYNOPSIS

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;
$p->parse_file(*F);
HTML::Parser version 2 style subclassing and method call
backs:
{
   package MyParser;
   use base 'HTML::Parser';
   sub start {
      my($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");

DESCRIPTION

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 actu
ally "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". It
is a "HTML::Parser" subclass that allows a more conven
tional program structure.

METHODS

The following method is used to construct a new
"HTML::Parser" object:

$p = HTML::Parser->new( %options_and_handlers ): This class method creates a new "HTML::Parser" object
and returns it. Key/value pair arguments may be pro
vided 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 refer
ence. Multiple handlers may also be assigned with the
'handlers => [%handlers]' option. See examples below.; If new() is called without any arguments, it will cre
ate 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 => [@ar

ray, "event,text"],

});
This creates a new parser object that stores the event type and the original text in @array for text and com ment events.
The following methods feed the HTML document to the "HTML::Parser" object:
$p->parse( $string ): Parse $string as the next chunk of the HTML document.
The return value is normally a reference to the parser
object (i.e. $p). Handlers invoked should not attempt
modify the $string in-place until $p->parse returns.; If an invoked event handler aborts parsing by calling
$p->eof, then $p->parse() will return a FALSE value.
$p->parse( $code_ref ): If a code reference is passed in as the argument to
parse then the chunks to parse is obtained by invoking
this function repeatedly. Parsing continues until the
function returns an empty (or undefined) result. When
this happens $p->eof is automatically signalled.; Parsing will also abort if one of the event handlers
call $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.
$p->parse_file( $file ): Parse text directly from a file. The $file argument
can be a filename, an open file handle, or a reference
to a an open file handle.; 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 val
ues 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.
$p->eof: Signals the end of the HTML document. Calling the
$p->eof method outside a handler callback will flush
any remaining buffered text (which triggers the "text"
event if there is any remaining text).; Calling $p->eof inside a handler will terminate pars
ing 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 docu ments 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 corre sponding 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:
$p->strict_comment( [$bool] ): By default, comments are terminated by the first
occurrence of "-->". This is the behaviour of most
popular browsers (like Netscape and MSIE), but it is
not correct according to the official HTML standard.
Officially, you need an even number of "--" tokens
before the closing ">" is recognized and there may not
be anything but whitespace between an even and an odd
"--".; The official behaviour is enabled by enabling this
attribute.
$p->strict_names( [$bool] ): By default, almost anything is allowed in tag and
attribute names. This is the behaviour of most popu
lar browsers and allows us to parse some broken tags
with invalid attr values like:

<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.
$p->boolean_attribute_value( $val ): This method sets the value reported for boolean
attributes inside HTML start tags. By default, the
name of the attribute is also used as its value. This
affects the values reported for "tokens" and "attr"
argspecs.
$p->xml_mode( [$bool] ): Enabling this attribute changes the parser to allow
some XML constructs such as empty element tags and XML processing instructions. It disables forcing tag and attribute names to lower case when they are reported
by the "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 arti
ficial 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.
$p->unbroken_text( [$bool] ): By default, blocks of text are given to the text han
dler as soon as possible (but the parser makes sure to
always break text at the boundary between whitespace
and non-whitespace so single words and entities always
can be decoded safely). This might create breaks that
make it hard to do transformations on the text. When
this attribute is enabled, blocks of text are always
reported in one piece. This will delay the text event
until the following (non-text) event has been recog
nized by the parser.; Note that the "offset" argspec will give you the off
set 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.
$p->marked_sections( [$bool] ): By default, section markings like <![CDATA[...]]> are
treated like ordinary text. When this attribute is
enabled section markings are honoured.; There are currently no events associated with the
marked section markup, but the text can be returned as
"skipped_text".
$p->attr_encoded( [$bool] ): By default, the "attr" and @attr argspecs will have
general entities for attribute values decoded.
Enabling this attribute leaves entities alone.
$p->case_sensititve( [$bool] ): By default, tagnames and attribute names are
down-cased. Enabling this attribute leave them as
found in the HTML source document.
As markup and text is recognized, handlers are invoked. The following method is used to set up handlers for dif ferent events:
$p->handler( event => subroutine, argspec ) $p->handler( event => method_name, argspec ) $p->handler( event => @accum, argspec ) $p->handler( event => "" ); $p->handler( event => undef ); $p->handler( event );: This method assigns a subroutine, method, or array to
handle an event.; Event is one of "text", "start", "end", "declaration",
"comment", "process", "start_document", "end_document"
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.; Any return values from handler callback routines/meth
ods 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 excep tion will be raised if it tries.; Examples:

$p->handler(start => "start", 'self, attr, at

trseq, 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 in most cases equivalent to $p->han
dler(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 assosiated 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:
$p->ignore_tags( TAG, ... ): Any "start" and "end" events involving any of the tags
given are suppressed.
$p->report_tags( TAG, ... ): Any "start" and "end" events involving any of the tags
not given are suppressed.
$p->ignore_elements( TAG, ... ): Both the "start" and the "end" event as well as any
events that would be reported in between are sup
pressed. The ignored elements can contain nested
occurences of itself. Example:

$p->ignore_elements(qw(script style));; The "script" and "style" tags will always nest prop
erly 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.
Argspec
Argspec is a string containing a comma separated list that describes the information reported by the event. The fol lowing argspec identifier names can be used:
"self": Self causes the current object to be passed to the
handler. If the handler is a method, this must be the
first element in the argspec.; An alternative to passing self as an argspec is to
register closures that capture $self by themselves as
handlers. Unfortunately this creates a circular ref
erences which prevents the HTML::Parser object from
being garbage collected. Using the "self" argspec
avoids this problem.
"tokens": Tokens causes a reference to an array of token strings
to be passed. The strings are exactly as they were
found in the original text, no decoding or case
changes are applied.; 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
(always one token).; For "process" events, this contains the process
instructions (always one token).; This passes "undef" for "text" events.
"tokenpos": Tokenpos causes a reference to an array of token posi
tions to be passed. For each string that appears in
"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 trig
gered 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 off
sets.
"token0": Token0 causes the original text of the first token
string to be passed. This should always be the same
as $tokens->[0].; 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": This is the element name (or generic identifier in SGML jargon) for start and end tags. Since HTML is
case insensitive this name is forced to lower case to
ease string matching.; Since XML is case sensitive, the tagname case is not
changed when "xml_mode" is enabled. 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.
"tag": Same as "tagname", 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".
"attr": Attr causes a reference to a hash of attribute
name/value pairs to be passed.; 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" 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 are removed.
"attrseq": Attrseq causes a reference to an array of attribute
names to be passed. This can be useful if you want to
walk the "attr" 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.
@attr: Basically same as "attr", 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 pass no values for events besides "start".
"text": Text causes the source text (including markup element
delimiters) to be passed.
"dtext": Dtext causes the decoded text to be passed. General
entities are automatically decoded unless the event
was inside a CDATA section or was between literal
start and end tags ("script", "style", "xmp", and
"plaintext").; The Unicode character set is assumed for entity decod
ing. With perl version < 5.7.1 only the Latin1 range
is supported, and entities for characters outside the
0..255 range is left unchanged.; This passes undef except for "text" events.
"is_cdata": Is_cdata causes a TRUE value to be passed if the event
is inside a CDATA section or is between literal start
and end tags ("script", "style", "xmp", and "plain
text").; When the flag is FALSE for a text event, then you
should normally either use "dtext" or decode the enti
ties yourself before the text is processed further.
"skipped_text": Skipped_text returns the concatenated text of all the
events that has been skipped since the last time an
event was reported. Events might be skipped because
no handler is registered for them or because some fil
ter applies. Skipped text also include marked section
markup, since there is no events that can catch them.; If 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".
"offset": Offset causes the byte position in the HTML document
of the start of the event to be passed. The first
byte in the document is 0.
"length": Length causes the number of bytes of the source text
of the event to be passed.
"offset_end": Offset_end causes the byte position in the HTML docu
ment of the end of the event to be passed. This is
the same as "offset" + "length".
"event": Event causes the event name to be passed.; The event name is one of "text", "start", "end", "dec
laration", "comment", "process", "start_document",
"end_document" 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 to be reported.
"column": Column causes the column number of the start of the
event to be passed. The first column on a line is 0.
'...': A literal string of 0 to 255 characters enclosed in
single (') or double (") quotes is passed as entered.
"undef": Pass an undefined value. Useful as padding where the
same handler routine is registered for multiple
events.
The whole argspec string can be wrapped up in '@{...}' to signal that resulting event array should be flatten. 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 one will end up with [["foo"], ["bar"]] and the second one with ["foo", "bar"] in the handler target array.
Events
Handlers for the following events can be registered:
"text": This event is triggered when plain text (characters)
is recognized. The text may contain multiple lines.
A sequence of text may be broken between several text
events unless $p->unbroken_text is enabled.; The parser will make sure that it does not break a
word or a sequence of whitespace between two text
events.
"start": This event is triggered when a start tag is recog
nized.; Example:

<A HREF="http://www.perl.com/">; "end"
This event is triggered when an end tag is recognized.

Example:

</A>

"declaration"

This event is triggered when a markup declaration is recognized.

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"

This event is triggered when a markup comment is rec
ognized.

Example:



"process"

This event is triggered when a processing instructions
markup is recognized.

The format and content of processing instructions is
system and application dependent.

Examples:

<? HTML processing instructions >
<? XML processing instructions ?>

"start_document"

This event is triggered before any other events for a
new document. A handler for it can be used to ini
tialize stuff. There is no document text associated
with this event.

"end_document"

This event is triggered when $p->eof called and after
any remaining text is flushed. There is no document
text associated with this event.

"default"

This event is triggered for events that do not have a
specific handler. You can set up a handler for this
event to catch stuff you did not want to catch explic
itly.

VERSION 2 COMPATIBILITY

When an "HTML::Parser" object is constructed with no argu
ments, 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_cda; ta");
$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.

SUBCLASSING

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().

EXAMPLES

The first simple example shows how you might strip out comments from an HTML document. We achieve this by set ting 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 sigle 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 "0;; 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.

BUGS

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 recog nize comments where there is something other than whites
pace 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.

DIAGNOSTICS

The following messages may be produced by HTML::Parser.
The notation in this listing is the same as used in perl
diag:

Not a reference to a hash: (F) The object blessed into or subclassed from
HTML::Parser is not a hash as required by the
HTML::Parser methods.
Bad signature in parser state object at %p: (F) The _hparser_xs_state element does not refer to a
valid state structure. Something must have changed
the internal value stored in this hash element, or the
memory has been overwritten.
_hparser_xs_state element is not a reference: (F) The _hparser_xs_state element has been destroyed.
Can't find '_hparser_xs_state' element in HTML::Parser hash: (F) The _hparser_xs_state element is missing from the
parser hash. It was either deleted, or not created
when the object was created.
API version %s not supported by HTML::Parser %s: (F) The constructor option 'api_version' with an argu
ment greater than or equal to 4 is reserved for future
extentions.
Bad constructor option '%s': (F) An unknown constructor option key was passed to
the new() or init() methods.
Parse loop not allowed: (F) A handler invoked the parse() or parse_file() method. This is not permitted.
marked sections not supported: (F) The $p->marked_sections() method was invoked in a HTML::Parser module that was compiled without support
for marked sections.
Unknown boolean attribute (%d): (F) Something is wrong with the internal logic that
set up aliases for boolean attributes.
Only code or array references allowed as handler: (F) The second argument for $p->handler must be either
a subroutine reference, then name of a subroutine or
method, or a reference to an array.
No handler for %s events: (F) The first argument to $p->handler must be a valid
event name; i.e. one of "start", "end", "text", "pro
cess", "declaration" or "comment".
Unrecognized identifier %s in argspec: (F) The identifier is not a known argspec name. Use
one of the names mentioned in the argspec section
above.
Literal string is longer than 255 chars in argspec: (F) The current implementation limits the length of
literals in an argspec to 255 characters. Make the
literal shorter.
Backslash reserved for literal string in argspec: (F) The backslash character "
argspec literals. It is reserved to permit quoting
inside a literal in a later version.
Unterminated literal string in argspec: (F) The terminating quote character for a literal was
not found.
Bad argspec (%s): (F) Only identifier names, literals, spaces and commas
are allowed in argspecs.
Missing comma separator in argspec: (F) Identifiers in an argspec must be separated with
",".

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