XML::XPath(3pm) User Contributed Perl Documentation XML::XPath(3pm)
NAME
XML::XPath - Parse and evaluate XPath statements.
VERSION
Version 1.48
DESCRIPTION
This module aims to comply exactly to the XPath specification at
http://www.w3.org/TR/xpath and yet allow extensions to be added in the
form of functions.Modules such as XSLT and XPointer may need to do this
as they support functionality beyond XPath.
SYNOPSIS
use XML::XPath;
use XML::XPath::XMLParser;
my $xp = XML::XPath->new(filename => 'test.xhtml');
my $nodeset = $xp->find('/html/body/p'); # find all paragraphs
foreach my $node ($nodeset->get_nodelist) {
print "FOUND\n\n",
XML::XPath::XMLParser::as_string($node),
"\n\n";
}
DETAILS
There is an awful lot to all of this, so bear with it - if you stick
it out it should be worth it. Please get a good understanding of XPath
by reading the spec before asking me questions. All of the classes and
parts herein are named to be synonymous with the names in the
specification, so consult that if you don't understand why I'm doing
something in the code.
Currently, it supports XPath 1.0 with a small number of XPath 2.0
functions. See XML::XPath::Function for the complete list of predefined
functions.
METHODS
The API of XML::XPath itself is extremely simple to allow you to get
going almost immediately. The deeper API's are more complex, but you
shouldn't have to touch most of that.
new()
This constructor follows the often seen named parameter method call.
Parameters you can use are: filename, parser, xml, ioref and context.
The filename parameter specifies an XML file to parse. The xml
parameter specifies a string to parse, and the ioref parameter
specifies an ioref to parse. The context option allows you to
specify a context node. The context node has to be in the format of a
node as specified in XML::XPath::XMLParser. The 4 parameters
filename, xml, ioref and context are mutually exclusive - you should
only specify one (if you specify anything other than context, the
context node is the root of your document). The parser option allows
you to pass in an already prepared XML::Parser object, to save you
having to create more than one in your application (if, for example,
you are doing more than just XPath).
my $xp = XML::XPath->new( context => $node );
It is very much recommended that you use only 1 XPath object
throughout the life of your application. This is because the object
(and it's sub-objects) maintain certain bits of state information
that will be useful (such as XPath variables) to later calls to
find(). It's also a good idea because you'll use less memory this way.
find($path, [$context])
The find function takes an XPath expression (a string) and returns
either an XML::XPath::NodeSet object containing the nodes it found (or
empty if no nodes matched the path), or one of XML::XPath::Literal (a
string), XML::XPath::Number or XML::XPath::Boolean. It should always
return something - and you can use ->isa() to find out what it
returned. If you need to check how many nodes it found you should check
$nodeset->size. See XML::XPath::NodeSet. An optional second parameter
of a context node allows you to use this method repeatedly, for example
XSLT needs to do this.
findnodes($path, [$context])
Returns a list of nodes found by $path, optionally in context $context.
In scalar context returns an XML::XPath::NodeSet object.
matches($node, $path, [$context])
Returns true if the node matches the path (optionally in context
$context).
findnodes_as_string($path, [$context])
Returns the nodes found reproduced as XML.The result isn't guaranteed
to be valid XML though.
findvalue($path, [$context])
Returns either a "XML::XPath::Literal", a "XML::XPath::Boolean" or a
"XML::XPath::Number" object.If the path returns a
NodeSet,$nodeset->to_literal is called automatically for you (and thus
a "XML::XPath::Literal" is returned).Note that for each of the objects
stringification is overloaded, so you can just print the value found,
or manipulate it in the ways you would a normal perl value (e.g. using
regular expressions).
exists($path, [$context])
Returns true if the given path exists.
getNodeText($path)
Returns the XML::XPath::Literal for a particular XML node. Returns a
string if exists or '' (empty string) if the node doesn't exist.
setNodeText($path, $text)
Sets the text string for a particular XML node. The node can be an
element or an attribute. If the node to be set is an attribute, and the
attribute node does not exist, it will be created automatically.
createNode($path)
Creates the node matching the $path given. If part of the path given or
all of the path do not exist, the necessary nodes will be created
automatically.
set_namespace($prefix, $uri)
Sets the namespace prefix mapping to the uri.
Normally in "XML::XPath" the prefixes in XPath node test take their
context from the current node. This means that foo:bar will always
match an element <foo:bar> regardless of the namespace that the
prefix foo is mapped to (which might even change within the document,
resulting in unexpected results). In order to make prefixes in XPath
node tests actually map to a real URI, you need to enable that via a
call to the set_namespace method of your "XML::XPath" object.
clear_namespaces()
Clears all previously set namespace mappings.
$XML::XPath::Namespaces
Set this to 0 if you don't want namespace processing to occur. This
will make everything a little (tiny) bit faster, but you'll suffer for
it, probably.
Node Object Model
See XML::XPath::Node, XML::XPath::Node::Element,
XML::XPath::Node::Text, XML::XPath::Node::Comment,
XML::XPath::Node::Attribute, XML::XPath::Node::Namespace, and
XML::XPath::Node::PI.
On Garbage Collection
XPath nodes work in a special way that allows circular references, and
yet still lets Perl's reference counting garbage collector to clean up
the nodes after use. This should be totally transparent to the
user, with one caveat: If you free your tree before letting go of a
sub-tree,consider that playing with fire and you may get burned. What
does this mean to the average user? Not much. Provided you don't free
(or let go out of scope) either the tree you passed to XML::XPath->new,
or if you didn't pass a tree, and passed a filename or IO-ref, then
provided you don't let the XML::XPath object go out of scope before
you let results of find() and its friends go out of scope, then
you'll be fine. Even if you do let the tree go out of scope before
results, you'll probably still be fine. The only case where you may
get stung is when the last part of your path/query is either an
ancestor or parent axis. In that case the worst that will happen is
you'll end up with a circular reference that won't get cleared until
interpreter destruction time.You can get around that by explicitly
calling $node->DESTROY on each of your result nodes, if you really need
to do that.
Mail me direct if that's not clear. Note that it's not doom and gloom.
It's by no means perfect,but the worst that will happen is a long
running process could leak memory. Most long running processes will
therefore be able to explicitly be careful not to free the tree (or
XML::XPath object) before freeing results.AxKit, an application that
uses XML::XPath, does this and I didn't have to make any changes to
the code - it's already sensible programming.
If you really don't want all this to happen, then set the variable
$XML::XPath::SafeMode, and call $xp->cleanup() on the XML::XPath object
when you're finished, or $tree->dispose() if you have a tree instead.
Example
Please see the test files in t/ for examples on how to use XPath.
AUTHOR
Original author Matt Sergeant, "<matt at sergeant.org>"
Currently maintained by Mohammad S Anwar, "<mohammad.anwar at
yahoo.com>"
SEE ALSO
XML::XPath::Function, XML::XPath::Literal, XML::XPath::Boolean,
XML::XPath::Number, XML::XPath::XMLParser, XML::XPath::NodeSet,
XML::XPath::PerlSAX, XML::XPath::Builder.
LICENSE AND COPYRIGHT
This module is copyright 2000 AxKit.com Ltd. This is free software,
and as such comes with NO WARRANTY. No dates are used in this module.
You may distribute this module under the terms of either the Gnu GPL,
or the Artistic License (the same terms as Perl itself).
For support, please subscribe to the Perl-XML
<http://listserv.activestate.com/mailman/listinfo/perl-xml> mailing
list at the URL
perl v5.34.0 2022-08-13 XML::XPath(3pm)
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