html::parser.3

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.\" ========================================================================
.\"
.IX Title "Parser 3"
.TH Parser 3 "2007-01-12" "perl v5.10.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
HTML::Parser \- HTML parser class
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& use HTML::Parser ();
\&
\& # Create parser object
\& $p = HTML::Parser\->new( api_version => 3,
\&                         start_h => [\e&start, "tagname, attr"],
\&                         end_h   => [\e&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);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Objects of the \f(CW\*(C`HTML::Parser\*(C'\fR class will recognize markup and
separate it from plain text (alias data content) in \s-1HTML\s0
documents.  As different kinds of markup and text are recognized, the
corresponding event handlers are invoked.
.PP
\&\f(CW\*(C`HTML::Parser\*(C'\fR is not a generic \s-1SGML\s0 parser.  We have tried to
make it able to deal with the \s-1HTML\s0 that is actually \*(L"out there\*(R", 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 \s-1HTML\s0
specifications from W3C.  Where there is disagreement, there is often
an option that you can enable to get the official behaviour.
.PP
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.
.PP
If event driven parsing does not feel right for your application, you
might want to use \f(CW\*(C`HTML::PullParser\*(C'\fR.  This is an \f(CW\*(C`HTML::Parser\*(C'\fR
subclass that allows a more conventional program structure.
.SH "METHODS"
.IX Header "METHODS"
The following method is used to construct a new \f(CW\*(C`HTML::Parser\*(C'\fR object:
.ie n .IP "$p\fR = HTML::Parser\->new( \f(CW%options_and_handlers )" 4
.el .IP "\f(CW$p\fR = HTML::Parser\->new( \f(CW%options_and_handlers\fR )" 4
.IX Item "$p = HTML::Parser->new( %options_and_handlers )"
This class method creates a new \f(CW\*(C`HTML::Parser\*(C'\fR 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.
.Sp
If a top level key is in the form \*(L"<event>_h\*(R" (e.g., \*(L"text_h\*(R") 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.
.Sp
If \fInew()\fR is called without any arguments, it will create a parser that
uses callback methods compatible with version 2 of \f(CW\*(C`HTML::Parser\*(C'\fR.
See the section on \*(L"version 2 compatibility\*(R" below for details.
.Sp
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.
.Sp
Examples:
.Sp
.Vb 2
\& $p = HTML::Parser\->new(api_version => 3,
\&                        text_h => [ sub {...}, "dtext" ]);
.Ve
.Sp
This creates a new parser object with a text event handler subroutine
that receives the original text with general entities decoded.
.Sp
.Vb 2
\& $p = HTML::Parser\->new(api_version => 3,
\&                        start_h => [ \*(Aqmy_start\*(Aq, "self,tokens" ]);
.Ve
.Sp
This creates a new parser object with a start event handler method
that receives the \f(CW$p\fR and the tokens array.
.Sp
.Vb 4
\& $p = HTML::Parser\->new(api_version => 3,
\&                        handlers => { text => [\e@array, "event,text"],
\&                                      comment => [\e@array, "event,text"],
\&                                    });
.Ve
.Sp
This creates a new parser object that stores the event type and the
original text in \f(CW@array\fR for text and comment events.
.PP
The following methods feed the \s-1HTML\s0 document
to the \f(CW\*(C`HTML::Parser\*(C'\fR object:
.ie n .IP "$p\fR\->parse( \f(CW$string )" 4
.el .IP "\f(CW$p\fR\->parse( \f(CW$string\fR )" 4
.IX Item "$p->parse( $string )"
Parse \f(CW$string\fR as the next chunk of the \s-1HTML\s0 document.  The return
value is normally a reference to the parser object (i.e. \f(CW$p\fR).
Handlers invoked should not attempt to modify the \f(CW$string\fR in-place until
\&\f(CW$p\fR\->parse returns.
.Sp
If an invoked event handler aborts parsing by calling \f(CW$p\fR\->eof, then
\&\f(CW$p\fR\->\fIparse()\fR will return a \s-1FALSE\s0 value.
.ie n .IP "$p\fR\->parse( \f(CW$code_ref )" 4
.el .IP "\f(CW$p\fR\->parse( \f(CW$code_ref\fR )" 4
.IX Item "$p->parse( $code_ref )"
If a code reference is passed as the argument to be parsed, then the
chunks to be parsed are obtained by invoking this function repeatedly.
Parsing continues until the function returns an empty (or undefined)
result.  When this happens \f(CW$p\fR\->eof is automatically signaled.
.Sp
Parsing will also abort if one of the event handlers calls \f(CW$p\fR\->eof.
.Sp
The effect of this is the same as:
.Sp
.Vb 8
\& while (1) {
\&    my $chunk = &$code_ref();
\&    if (!defined($chunk) || !length($chunk)) {
\&        $p\->eof;
\&        return $p;
\&    }
\&    $p\->parse($chunk) || return undef;
\& }
.Ve
.Sp
But it is more efficient as this loop runs internally in \s-1XS\s0 code.
.ie n .IP "$p\fR\->parse_file( \f(CW$file )" 4
.el .IP "\f(CW$p\fR\->parse_file( \f(CW$file\fR )" 4
.IX Item "$p->parse_file( $file )"
Parse text directly from a file.  The \f(CW$file\fR argument can be a
filename, an open file handle, or a reference to an open file
handle.
.Sp
If \f(CW$file\fR contains a filename and the file can't be opened, then the
method returns an undefined value and $! tells why it failed.
Otherwise the return value is a reference to the parser object.
.Sp
If a file handle is passed as the \f(CW$file\fR argument, then the file will
normally be read until \s-1EOF\s0, but not closed.
.Sp
If an invoked event handler aborts parsing by calling \f(CW$p\fR\->eof,
then \f(CW$p\fR\->\fIparse_file()\fR may not have read the entire file.
.Sp
On systems with multi-byte line terminators, the values passed for the
offset and length argspecs may be too low if \fIparse_file()\fR is called on
a file handle that is not in binary mode.
.Sp
If a filename is passed in, then \fIparse_file()\fR will open the file in
binary mode.
.ie n .IP "$p\->eof" 4
.el .IP "\f(CW$p\fR\->eof" 4
.IX Item "$p->eof"
Signals the end of the \s-1HTML\s0 document.  Calling the \f(CW$p\fR\->eof method
outside a handler callback will flush any remaining buffered text
(which triggers the \f(CW\*(C`text\*(C'\fR event if there is any remaining text).
.Sp
Calling \f(CW$p\fR\->eof inside a handler will terminate parsing at that point
and cause \f(CW$p\fR\->parse to return a \s-1FALSE\s0 value.  This also terminates
parsing by \f(CW$p\fR\->\fIparse_file()\fR.
.Sp
After \f(CW$p\fR\->eof has been called, the \fIparse()\fR and \fIparse_file()\fR methods
can be invoked to feed new documents with the parser object.
.Sp
The return value from \fIeof()\fR is a reference to the parser object.
.PP
Most parser options are controlled by boolean attributes.
Each boolean attribute is enabled by calling the corresponding method