1XPath(3)              User Contributed Perl Documentation             XPath(3)
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NAME

6       XML::XPath - a set of modules for parsing and evaluating XPath
7       statements
8

DESCRIPTION

10       This module aims to comply exactly to the XPath specification at
11       http://www.w3.org/TR/xpath and yet allow extensions to be added in the
12       form of functions. Modules such as XSLT and XPointer may need to do
13       this as they support functionality beyond XPath.
14

SYNOPSIS

16           use XML::XPath;
17           use XML::XPath::XMLParser;
18
19           my $xp = XML::XPath->new(filename => 'test.xhtml');
20
21           my $nodeset = $xp->find('/html/body/p'); # find all paragraphs
22
23           foreach my $node ($nodeset->get_nodelist) {
24               print "FOUND\n\n",
25                   XML::XPath::XMLParser::as_string($node),
26                   "\n\n";
27           }
28

DETAILS

30       There's an awful lot to all of this, so bear with it - if you stick it
31       out it should be worth it. Please get a good understanding of XPath by
32       reading the spec before asking me questions. All of the classes and
33       parts herein are named to be synonimous with the names in the
34       specification, so consult that if you don't understand why I'm doing
35       something in the code.
36

API

38       The API of XML::XPath itself is extremely simple to allow you to get
39       going almost immediately. The deeper API's are more complex, but you
40       shouldn't have to touch most of that.
41
42   new()
43       This constructor follows the often seen named parameter method call.
44       Parameters you can use are: filename, parser, xml, ioref and context.
45       The filename parameter specifies an XML file to parse. The xml
46       parameter specifies a string to parse, and the ioref parameter
47       specifies an ioref to parse. The context option allows you to specify a
48       context node. The context node has to be in the format of a node as
49       specified in XML::XPath::XMLParser. The 4 parameters filename, xml,
50       ioref and context are mutually exclusive - you should only specify one
51       (if you specify anything other than context, the context node is the
52       root of your document).  The parser option allows you to pass in an
53       already prepared XML::Parser object, to save you having to create more
54       than one in your application (if, for example, you're doing more than
55       just XPath).
56
57           my $xp = XML::XPath->new( context => $node );
58
59       It is very much recommended that you use only 1 XPath object throughout
60       the life of your application. This is because the object (and it's sub-
61       objects) maintain certain bits of state information that will be useful
62       (such as XPath variables) to later calls to find(). It's also a good
63       idea because you'll use less memory this way.
64
65   nodeset = find($path, [$context])
66       The find function takes an XPath expression (a string) and returns
67       either an XML::XPath::NodeSet object containing the nodes it found (or
68       empty if no nodes matched the path), or one of XML::XPath::Literal (a
69       string), XML::XPath::Number, or XML::XPath::Boolean. It should always
70       return something - and you can use ->isa() to find out what it
71       returned. If you need to check how many nodes it found you should check
72       $nodeset->size.  See XML::XPath::NodeSet. An optional second parameter
73       of a context node allows you to use this method repeatedly, for example
74       XSLT needs to do this.
75
76   findnodes($path, [$context])
77       Returns a list of nodes found by $path, optionally in context $context.
78       In scalar context returns an XML::XPath::NodeSet object.
79
80   findnodes_as_string($path, [$context])
81       Returns the nodes found reproduced as XML. The result is not guaranteed
82       to be valid XML though.
83
84   findvalue($path, [$context])
85       Returns either a "XML::XPath::Literal", a "XML::XPath::Boolean" or a
86       "XML::XPath::Number" object. If the path returns a NodeSet,
87       $nodeset->to_literal is called automatically for you (and thus a
88       "XML::XPath::Literal" is returned). Note that for each of the objects
89       stringification is overloaded, so you can just print the value found,
90       or manipulate it in the ways you would a normal perl value (e.g. using
91       regular expressions).
92
93   exists($path, [$context])
94       Returns true if the given path exists.
95
96   matches($node, $path, [$context])
97       Returns true if the node matches the path (optionally in context
98       $context).
99
100   getNodeText($path)
101       Returns the text string for a particular XML node.  Returns a string,
102       or undef if the node doesn't exist.
103
104   setNodeText($path, $text)
105       Sets the text string for a particular XML node.  The node can be an
106       element or an attribute.  If the node to be set is an attribute, and
107       the attribute node does not exist, it will be created automatically.
108
109   createNode($path)
110       Creates the node matching the path given.  If part of the path given,
111       or all of the path do not exist, the necessary nodes will be created
112       automatically.
113
114   set_namespace($prefix, $uri)
115       Sets the namespace prefix mapping to the uri.
116
117       Normally in XML::XPath the prefixes in XPath node tests take their
118       context from the current node. This means that foo:bar will always
119       match an element <foo:bar> regardless of the namespace that the prefix
120       foo is mapped to (which might even change within the document,
121       resulting in unexpected results). In order to make prefixes in XPath
122       node tests actually map to a real URI, you need to enable that via a
123       call to the set_namespace method of your XML::XPath object.
124
125   clear_namespaces()
126       Clears all previously set namespace mappings.
127
128   $XML::XPath::Namespaces
129       Set this to 0 if you don't want namespace processing to occur. This
130       will make everything a little (tiny) bit faster, but you'll suffer for
131       it, probably.
132

Node Object Model

134       See XML::XPath::Node, XML::XPath::Node::Element,
135       XML::XPath::Node::Text, XML::XPath::Node::Comment,
136       XML::XPath::Node::Attribute, XML::XPath::Node::Namespace, and
137       XML::XPath::Node::PI.
138

On Garbage Collection

140       XPath nodes work in a special way that allows circular references, and
141       yet still lets Perl's reference counting garbage collector to clean up
142       the nodes after use. This should be totally transparent to the user,
143       with one caveat: If you free your tree before letting go of a sub-tree,
144       consider that playing with fire and you may get burned. What does this
145       mean to the average user? Not much. Provided you don't free (or let go
146       out of scope) either the tree you passed to XML::XPath->new, or if you
147       didn't pass a tree, and passed a filename or IO-ref, then provided you
148       don't let the XML::XPath object go out of scope before you let results
149       of find() and its friends go out of scope, then you'll be fine. Even if
150       you do let the tree go out of scope before results, you'll probably
151       still be fine. The only case where you may get stung is when the last
152       part of your path/query is either an ancestor or parent axis. In that
153       case the worst that will happen is you'll end up with a circular
154       reference that won't get cleared until interpreter destruction time.
155       You can get around that by explicitly calling $node->DESTROY on each of
156       your result nodes, if you really need to do that.
157
158       Mail me direct if that's not clear. Note that it's not doom and gloom.
159       It's by no means perfect, but the worst that will happen is a long
160       running process could leak memory. Most long running processes will
161       therefore be able to explicitly be careful not to free the tree (or
162       XML::XPath object) before freeing results. AxKit, an application that
163       uses XML::XPath, does this and I didn't have to make any changes to the
164       code - it's already sensible programming.
165
166       If you really don't want all this to happen, then set the variable
167       $XML::XPath::SafeMode, and call $xp->cleanup() on the XML::XPath object
168       when you're finished, or $tree->dispose() if you have a tree instead.
169

Example

171       Please see the test files in t/ for examples on how to use XPath.
172

Support/Author

174       This module is copyright 2000 AxKit.com Ltd. This is free software, and
175       as such comes with NO WARRANTY. No dates are used in this module. You
176       may distribute this module under the terms of either the Gnu GPL,  or
177       the Artistic License (the same terms as Perl itself).
178
179       For support, please subscribe to the Perl-XML mailing list at the URL
180       http://listserv.activestate.com/mailman/listinfo/perl-xml
181
182       Matt Sergeant, matt@sergeant.org
183

SEE ALSO

185       XML::XPath::Literal, XML::XPath::Boolean, XML::XPath::Number,
186       XML::XPath::XMLParser, XML::XPath::NodeSet, XML::XPath::PerlSAX,
187       XML::XPath::Builder.
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191perl v5.12.0                      2003-01-26                          XPath(3)
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