XML::Parser
Parser(3) User Contributed Perl Documentation Parser(3)
NAME
XML::Parser - A perl module for parsing XML documents
SYNOPSIS
use XML::Parser;
$p1 = new XML::Parser(Style => 'Debug');
$p1->parsefile('REC-xml-19980210.xml');
$p1->parse('<foo id="me">Hello World</foo>');
# Alternative
$p2 = new XML::Parser(Handlers => {Start => \&handle_start,
End => \&handle_end,
Char => \&handle_char});
$p2->parse($socket);
# Another alternative
$p3 = new XML::Parser(ErrorContext => 2);
$p3->setHandlers(Char => \&text,
Default => \&other);
open(FOO, 'xmlgenerator |');
$p3->parse(*FOO, ProtocolEncoding => 'ISO-8859-1');
close(FOO);
$p3->parsefile('junk.xml', ErrorContext => 3);
DESCRIPTION
This module provides ways to parse XML documents. It is built on top of
XML::Parser::Expat, which is a lower level interface to James Clark's
expat library. Each call to one of the parsing methods creates a new
instance of XML::Parser::Expat which is then used to parse the docu-
ment. Expat options may be provided when the XML::Parser object is
created. These options are then passed on to the Expat object on each
parse call. They can also be given as extra arguments to the parse
methods, in which case they override options given at XML::Parser cre-
ation time.
The behavior of the parser is controlled either by ""Style"" and/or
""Handlers"" options, or by "setHandlers" method. These all provide
mechanisms for XML::Parser to set the handlers needed by
XML::Parser::Expat. If neither "Style" nor "Handlers" are specified,
then parsing just checks the document for being well-formed.
When underlying handlers get called, they receive as their first param-
eter the Expat object, not the Parser object.
METHODS
new This is a class method, the constructor for XML::Parser. Options
are passed as keyword value pairs. Recognized options are:
* Style
This option provides an easy way to create a given style of
parser. The built in styles are: "Debug", "Subs", "Tree",
"Objects", and "Stream". These are all defined in separate
packages under "XML::Parser::Style::*", and you can find fur-
ther documentation for each style both below, and in those
packages.
Custom styles can be provided by giving a full package name
containing at least one '::'. This package should then have
subs defined for each handler it wishes to have installed. See
"STYLES" below for a discussion of each built in style.
* Handlers
When provided, this option should be an anonymous hash contain-
ing as keys the type of handler and as values a sub reference
to handle that type of event. All the handlers get passed as
their 1st parameter the instance of expat that is parsing the
document. Further details on handlers can be found in "HAN-
DLERS". Any handler set here overrides the corresponding han-
dler set with the Style option.
* Pkg
Some styles will refer to subs defined in this package. If not
provided, it defaults to the package which called the construc-
tor.
* ErrorContext
This is an Expat option. When this option is defined, errors
are reported in context. The value should be the number of
lines to show on either side of the line in which the error
occurred.
* ProtocolEncoding
This is an Expat option. This sets the protocol encoding name.
It defaults to none. The built-in encodings are: "UTF-8",
"ISO-8859-1", "UTF-16", and "US-ASCII". Other encodings may be
used if they have encoding maps in one of the directories in
the @Encoding_Path list. Check "ENCODINGS" for more information
on encoding maps. Setting the protocol encoding overrides any
encoding in the XML declaration.
* Namespaces
This is an Expat option. If this is set to a true value, then
namespace processing is done during the parse. See "Namespaces"
in XML::Parser::Expat for further discussion of namespace pro-
cessing.
* NoExpand
This is an Expat option. Normally, the parser will try to
expand references to entities defined in the internal subset.
If this option is set to a true value, and a default handler is
also set, then the default handler will be called when an
entity reference is seen in text. This has no effect if a
default handler has not been registered, and it has no effect
on the expansion of entity references inside attribute values.
* Stream_Delimiter
This is an Expat option. It takes a string value. When this
string is found alone on a line while parsing from a stream,
then the parse is ended as if it saw an end of file. The
intended use is with a stream of xml documents in a MIME multi-
part format. The string should not contain a trailing newline.
* ParseParamEnt
This is an Expat option. Unless standalone is set to "yes" in
the XML declaration, setting this to a true value allows the
external DTD to be read, and parameter entities to be parsed
and expanded.
* NoLWP
This option has no effect if the ExternEnt or ExternEntFin han-
dlers are directly set. Otherwise, if true, it forces the use
of a file based external entity handler.
* Non-Expat-Options
If provided, this should be an anonymous hash whose keys are
options that shouldn't be passed to Expat. This should only be
of concern to those subclassing XML::Parser.
setHandlers(TYPE, HANDLER [, TYPE, HANDLER [...]])
This method registers handlers for various parser events. It over-
rides any previous handlers registered through the Style or Handler
options or through earlier calls to setHandlers. By providing a
false or undefined value as the handler, the existing handler can
be unset.
This method returns a list of type, handler pairs corresponding to
the input. The handlers returned are the ones that were in effect
prior to the call.
See a description of the handler types in "HANDLERS".
parse(SOURCE [, OPT => OPT_VALUE [...]])
The SOURCE parameter should either be a string containing the whole
XML document, or it should be an open IO::Handle. Constructor
options to XML::Parser::Expat given as keyword-value pairs may fol-
low the SOURCE parameter. These override, for this call, any
options or attributes passed through from the XML::Parser instance.
A die call is thrown if a parse error occurs. Otherwise it will
return 1 or whatever is returned from the Final handler, if one is
installed. In other words, what parse may return depends on the
style.
parsestring
This is just an alias for parse for backwards compatibility.
parsefile(FILE [, OPT => OPT_VALUE [...]])
Open FILE for reading, then call parse with the open handle. The
file is closed no matter how parse returns. Returns what parse
returns.
parse_start([ OPT => OPT_VALUE [...]])
Create and return a new instance of XML::Parser::ExpatNB. Construc-
tor options may be provided. If an init handler has been provided,
it is called before returning the ExpatNB object. Documents are
parsed by making incremental calls to the parse_more method of this
object, which takes a string. A single call to the parse_done
method of this object, which takes no arguments, indicates that the
document is finished.
If there is a final handler installed, it is executed by the
parse_done method before returning and the parse_done method
returns whatever is returned by the final handler.
HANDLERS
Expat is an event based parser. As the parser recognizes parts of the
document (say the start or end tag for an XML element), then any han-
dlers registered for that type of an event are called with suitable
parameters. All handlers receive an instance of XML::Parser::Expat as
their first argument. See "METHODS" in XML::Parser::Expat for a discus-
sion of the methods that can be called on this object.
Init (Expat)
This is called just before the parsing of the document starts.
Final (Expat)
This is called just after parsing has finished, but only if no errors
occurred during the parse. Parse returns what this returns.
Start (Expat, Element [, Attr, Val [,...]])
This event is generated when an XML start tag is recognized. Element is
the name of the XML element type that is opened with the start tag. The
Attr & Val pairs are generated for each attribute in the start tag.
End (Expat, Element)
This event is generated when an XML end tag is recognized. Note that an
XML empty tag (<foo/>) generates both a start and an end event.
Char (Expat, String)
This event is generated when non-markup is recognized. The non-markup
sequence of characters is in String. A single non-markup sequence of
characters may generate multiple calls to this handler. Whatever the
encoding of the string in the original document, this is given to the
handler in UTF-8.
Proc (Expat, Target, Data)
This event is generated when a processing instruction is recognized.
Comment (Expat, Data)
This event is generated when a comment is recognized.
CdataStart (Expat)
This is called at the start of a CDATA section.
CdataEnd (Expat)
This is called at the end of a CDATA section.
Default (Expat, String)
This is called for any characters that don't have a registered handler.
This includes both characters that are part of markup for which no
events are generated (markup declarations) and characters that could
generate events, but for which no handler has been registered.
Whatever the encoding in the original document, the string is returned
to the handler in UTF-8.
Unparsed (Expat, Entity, Base, Sysid, Pubid, Notation)
This is called for a declaration of an unparsed entity. Entity is the
name of the entity. Base is the base to be used for resolving a rela-
tive URI. Sysid is the system id. Pubid is the public id. Notation is
the notation name. Base and Pubid may be undefined.
Notation (Expat, Notation, Base, Sysid, Pubid)
This is called for a declaration of notation. Notation is the notation
name. Base is the base to be used for resolving a relative URI. Sysid
is the system id. Pubid is the public id. Base, Sysid, and Pubid may
all be undefined.
ExternEnt (Expat, Base, Sysid, Pubid)
This is called when an external entity is referenced. Base is the base
to be used for resolving a relative URI. Sysid is the system id. Pubid
is the public id. Base, and Pubid may be undefined.
This handler should either return a string, which represents the con-
tents of the external entity, or return an open filehandle that can be
read to obtain the contents of the external entity, or return undef,
which indicates the external entity couldn't be found and will generate
a parse error.
If an open filehandle is returned, it must be returned as either a glob
(*FOO) or as a reference to a glob (e.g. an instance of IO::Handle).
A default handler is installed for this event. The default handler is
XML::Parser::lwp_ext_ent_handler unless the NoLWP option was provided
with a true value, otherwise XML::Parser::file_ext_ent_handler is the
default handler for external entities. Even without the NoLWP option,
if the URI or LWP modules are missing, the file based handler ends up
being used after giving a warning on the first external entity refer-
ence.
The LWP external entity handler will use proxies defined in the envi-
ronment (http_proxy, ftp_proxy, etc.).
Please note that the LWP external entity handler reads the entire
entity into a string and returns it, where as the file handler opens a
filehandle.
Also note that the file external entity handler will likely choke on
absolute URIs or file names that don't fit the conventions of the local
operating system.
The expat base method can be used to set a basename for relative path-
names. If no basename is given, or if the basename is itself a relative
name, then it is relative to the current working directory.
ExternEntFin (Expat)
This is called after parsing an external entity. It's not called unless
an ExternEnt handler is also set. There is a default handler installed
that pairs with the default ExternEnt handler.
If you're going to install your own ExternEnt handler, then you should
set (or unset) this handler too.
Entity (Expat, Name, Val, Sysid, Pubid, Ndata, IsParam)
This is called when an entity is declared. For internal entities, the
Val parameter will contain the value and the remaining three parameters
will be undefined. For external entities, the Val parameter will be
undefined, the Sysid parameter will have the system id, the Pubid
parameter will have the public id if it was provided (it will be unde-
fined otherwise), the Ndata parameter will contain the notation for
unparsed entities. If this is a parameter entity declaration, then the
IsParam parameter is true.
Note that this handler and the Unparsed handler above overlap. If both
are set, then this handler will not be called for unparsed entities.
Element (Expat, Name, Model)
The element handler is called when an element declaration is found.
Name is the element name, and Model is the content model as an
XML::Parser::Content object. See "XML::Parser::ContentModel Methods" in
XML::Parser::Expat for methods available for this class.
Attlist (Expat, Elname, Attname, Type, Default, Fixed)
This handler is called for each attribute in an ATTLIST declaration.
So an ATTLIST declaration that has multiple attributes will generate
multiple calls to this handler. The Elname parameter is the name of the
element with which the attribute is being associated. The Attname
parameter is the name of the attribute. Type is the attribute type,
given as a string. Default is the default value, which will either be
"#REQUIRED", "#IMPLIED" or a quoted string (i.e. the returned string
will begin and end with a quote character). If Fixed is true, then
this is a fixed attribute.
Doctype (Expat, Name, Sysid, Pubid, Internal)
This handler is called for DOCTYPE declarations. Name is the document
type name. Sysid is the system id of the document type, if it was pro-
vided, otherwise it's undefined. Pubid is the public id of the document
type, which will be undefined if no public id was given. Internal is
the internal subset, given as a string. If there was no internal sub-
set, it will be undefined. Internal will contain all whitespace, com-
ments, processing instructions, and declarations seen in the internal
subset. The declarations will be there whether or not they have been
processed by another handler (except for unparsed entities processed by
the Unparsed handler). However, comments and processing instructions
will not appear if they've been processed by their respective handlers.
* DoctypeFin (Parser)
This handler is called after parsing of the DOCTYPE declaration has
finished, including any internal or external DTD declarations.
XMLDecl (Expat, Version, Encoding, Standalone)
This handler is called for xml declarations. Version is a string con-
taing the version. Encoding is either undefined or contains an encoding
string. Standalone will be either true, false, or undefined if the
standalone attribute is yes, no, or not made respectively.
STYLES
Debug
This just prints out the document in outline form. Nothing special is
returned by parse.
Subs
Each time an element starts, a sub by that name in the package speci-
fied by the Pkg option is called with the same parameters that the
Start handler gets called with.
Each time an element ends, a sub with that name appended with an under-
score ("_"), is called with the same parameters that the End handler
gets called with.
Nothing special is returned by parse.
Tree
Parse will return a parse tree for the document. Each node in the tree
takes the form of a tag, content pair. Text nodes are represented with
a pseudo-tag of "0" and the string that is their content. For elements,
the content is an array reference. The first item in the array is a
(possibly empty) hash reference containing attributes. The remainder of
the array is a sequence of tag-content pairs representing the content
of the element.
So for example the result of parsing:
<foo><head id="a">Hello <em>there</em></head><bar>Howdy<ref/></bar>do</foo>
would be:
Tag Content
==================================================================
[foo, [{}, head, [{id => "a"}, 0, "Hello ", em, [{}, 0, "there"]],
bar, [ {}, 0, "Howdy", ref, [{}]],
0, "do"
]
]
The root document "foo", has 3 children: a "head" element, a "bar" ele-
ment and the text "do". After the empty attribute hash, these are rep-
resented in it's contents by 3 tag-content pairs.
Objects
This is similar to the Tree style, except that a hash object is created
for each element. The corresponding object will be in the class whose
name is created by appending "::" and the element name to the package
set with the Pkg option. Non-markup text will be in the ::Characters
class. The contents of the corresponding object will be in an anonymous
array that is the value of the Kids property for that object.
Stream
This style also uses the Pkg package. If none of the subs that this
style looks for is there, then the effect of parsing with this style is
to print a canonical copy of the document without comments or declara-
tions. All the subs receive as their 1st parameter the Expat instance
for the document they're parsing.
It looks for the following routines:
* StartDocument
Called at the start of the parse .
* StartTag
Called for every start tag with a second parameter of the element
type. The $_ variable will contain a copy of the tag and the %_
variable will contain attribute values supplied for that element.
* EndTag
Called for every end tag with a second parameter of the element
type. The $_ variable will contain a copy of the end tag.
* Text
Called just before start or end tags with accumulated non-markup
text in the $_ variable.
* PI
Called for processing instructions. The $_ variable will contain a
copy of the PI and the target and data are sent as 2nd and 3rd
parameters respectively.
* EndDocument
Called at conclusion of the parse.
ENCODINGS
XML documents may be encoded in character sets other than Unicode as
long as they may be mapped into the Unicode character set. Expat has
further restrictions on encodings. Read the xmlparse.h header file in
the expat distribution to see details on these restrictions.
Expat has built-in encodings for: "UTF-8", "ISO-8859-1", "UTF-16", and
"US-ASCII". Encodings are set either through the XML declaration encod-
ing attribute or through the ProtocolEncoding option to XML::Parser or
XML::Parser::Expat.
For encodings other than the built-ins, expat calls the function
load_encoding in the Expat package with the encoding name. This func-
tion looks for a file in the path list @XML::Parser::Expat::Encod-
ing_Path, that matches the lower-cased name with a '.enc' extension.
The first one it finds, it loads.
If you wish to build your own encoding maps, check out the XML::Encod-
ing module from CPAN.
AUTHORS
Larry Wall <larry@wall.org> wrote version 1.0.
Clark Cooper <coopercc@netheaven.com> picked up support, changed the
API for this version (2.x), provided documentation, and added some
standard package features.
Matt Sergeant <matt@sergeant.org> is now maintaining XML::Parser
perl v5.8.6 2003-08-18 Parser(3)
