1Dumper(3) User Contributed Perl Documentation Dumper(3)
2
6 XML::Dumper - Perl module for dumping Perl objects from/to XML
7
9 # ===== Using an object
10 use XML::Dumper;
11 $dump = new XML::Dumper;
12 $xml = $dump->pl2xml( $perl );
14 $perl = $dump->xml2pl( $xml );
15 $dump->pl2xml( $perl, "my_perl_data.xml.gz" );
16 # ===== Using function calls
18 use XML::Dumper;
19 $xml = pl2xml( $perl );
21 $perl = xml2pl( $xml );
22
24 use XML::Dumper;
25 my $dump = new XML::Dumper;
26 my $perl = '';
28 my $xml = '';
29 # ===== Convert Perl code to XML
31 $perl = [
32 {
33 fname => 'Fred',
34 lname => 'Flintstone',
35 residence => 'Bedrock'
36 },
37 {
38 fname => 'Barney',
39 lname => 'Rubble',
40 residence => 'Bedrock'
41 }
42 ];
43 $xml = $dump->pl2xml( $perl );
44 # ===== Dump to a file
46 my $file = "dump.xml";
47 $dump->pl2xml( $perl, $file );
48 # ===== Convert XML to Perl code
50 $xml = q|
51 <perldata>
52 <arrayref>
53 <item key="0">
54 <hashref>
55 <item key="fname">Fred</item>
56 <item key="lname">Flintstone</item>
57 <item key="residence">Bedrock</item>
58 </hashref>
59 </item>
60 <item key="1">
61 <hashref>
62 <item key="fname">Barney</item>
63 <item key="lname">Rubble</item>
64 <item key="residence">Bedrock</item>
65 </hashref>
66 </item>
67 </arrayref>
68 </perldata>
69 |;
70 my $perl = $dump->xml2pl( $xml );
72 # ===== Convert an XML file to Perl code
74 my $perl = $dump->xml2pl( $file );
75 # ===== And serialize Perl code to an XML file
77 $dump->pl2xml( $perl, $file );
78 # ===== USE COMPRESSION
80 $dump->pl2xml( $perl, $file.".gz" );
81 # ===== INCLUDE AN IN-DOCUMENT DTD
83 $dump->dtd;
84 my $xml_with_dtd = $dump->pl2xml( $perl );
85 # ===== USE EXTERNAL DTD
87 $dump->dtd( $file, $url );
88 my $xml_with_link_to_dtd = $dump->pl2xml( $perl );
89
91 XML::Dumper dumps Perl data to XML format. XML::Dumper can also read
92 XML data that was previously dumped by the module and convert it back
93 to Perl. You can use the module read the XML from a file and write the
94 XML to a file. Perl objects are blessed back to their original
95 packaging; if the modules are installed on the system where the perl
96 objects are reconstituted from xml, they will behave as expected.
97 Intuitively, if the perl objects are converted and reconstituted in the
98 same environment, all should be well. And it is.
99 Additionally, because XML benefits so nicely from compression,
101 XML::Dumper understands gzipped XML files. It does so with an optional
102 dependency on Compress::Zlib. So, if you dump a Perl variable with a
103 file that has an extension of '.xml.gz', it will store and compress the
104 file in gzipped format. Likewise, if you read a file with the
105 extension '.xml.gz', it will uncompress the file in memory before
106 parsing the XML back into a Perl variable.
107 Another fine challenge that this module rises to meet is that it
109 understands circular definitions and multiple references to a single
110 object. This includes doubly-linked lists, circular references, and the
111 so-called 'Flyweight' pattern of Object Oriented programming. So it can
112 take the gnarliest of your perl data, and should do just fine.
113 One caveat; XML::Dumper does not handle binary data. There have been
115 discussions in the expat mailing list archives discussing the
116 challenges associated with encoding binary data with XML. I chose the
117 cowardly path of making the problem a non-issue by not addressing it.
118 To store binary data, one could encode the data into ASCII before
119 encapsulating the data as XML, and then reverse the process to restore
120 the data. There are several Perl modules that one can use for this,
121 Convert::UU, for example.
122 FUNCTIONS AND METHODS
124 • new() - XML::Dumper constructor.
125 Creates a lean, mean, XML dumping machine. It's also completely at
127 your disposal.
128 • dtd -
130 Generates a Document Type Dictionary for the 'perldata' data type.
132 The default behaviour is to embed the DTD in the XML, thereby
133 creating valid XML. Given a filename, the DTD will be written out
134 to that file and the XML document for your Perl data will link to
135 the file. Given a filename and an URL, the DTD will be written out
136 the file and the XML document will link to the URL. XML::Dumper
137 doesn't try really hard to determine where your DTD's ought to go
138 or relative paths or anything, so be careful with what arguments
139 you supply this method, or just go with the default with the
140 embedded DTD. Between DTD's and Schemas, the potential for more
141 free-form data to be imported and exported becomes feasible.
142 Usage:
144 dtd(); # Causes XML to include embedded DTD
146 dtd( $file ); # DTD saved to $file; XML will link to $file
147 dtd( $file, $url ); # DTD saved to $file; XML will link to $url
148 dtd( 0 ); # Prevents XML from including embedded DTD
149 • pl2xml( $xml, [ $file ] ) -
151 (Also perl2xml(), for those who enjoy readability over brevity).
153 Converts Perl data to XML. If a second argument is given, then the
155 Perl data will be stored to disk as XML, using the second argument
156 as a filename.
157 Usage: See Synopsis
159 • xml2pl( $xml_or_filename, [ $callback ] ) -
161 (Also xml2perl(), for those who enjoy readability over brevity.)
163 Converts XML to a Perl datatype. If this method is given a second
165 argument, XML::Dumper will use the second argument as a callback
166 (if possible). If the first argument isn't XML and exists as a
167 file, that file will be read and its contents will be used as the
168 input XML.
169 Currently, the only supported invocation of callbacks is through
171 soft references. That is to say, the callback argument ought to be
172 a string that matches the name of a callable method for your
173 classes. If you have a congruent interface, this should work like a
174 peach. If your class interface doesn't have such a named method, it
175 won't be called.
176 • xml_compare( $xml1, $xml2 ) - Compares xml for content
178 Compares two dumped Perl data structures (that is, compares the
180 xml) for identity in content. Use this function rather than perl's
181 built-in string comparison. This function will return true for any
182 two perl data that are either deep clones of each other, or
183 identical. This method is exported by default.
184 • xml_identity( $xml1, $xml2 ) - Compares xml for identity
186 Compares two dumped Perl data structures (that is, compares the
188 xml) for identity in instantiation. This function will return true
189 for any two perl data that are identical, but not for deep clones
190 of each other. This method is also exported by default.
191
193 By default, the following methods are exported:
194 xml2pl, pl2xml, xml_compare, xml_identity
196
198 XML::Dumper has changed API since 0.4, as a response to a bug report
199 from PerlMonks. I felt it was necessary, as the functions simply didn't
200 work as advertised. That is, xml2pl really didnt accept xml as an
201 argument; what it wanted was an XML Parse tree. To correct for the API
202 change, simply don't parse the XML before feeding it to XML::Dumper.
203 XML::Dumper also has no understanding of typeglobs (references or not),
205 references to regular expressions, or references to Perl subroutines.
206 Turns out that Data::Dumper doesn't do references to Perl subroutines,
207 either, so at least I'm in somewhat good company.
208 XML::Dumper requires one perl module, available from CPAN
210 XML::Parser
212 XML::Parser itself relies on Clark Cooper's Expat implementation in
214 Perl, which in turn requires James Clark's expat package itself. See
215 the documentation for XML::Parser for more information.
216
218 The list of credits got so long that I had to move it to the Changes
219 file. Thanks to all those who've contributed with bug reports and
220 suggested features! Keep 'em coming!
221 I've had ownership of the module since June of 2002, and very much
223 appreciate requests on how to make the module better. It has served me
224 well, both as a learning tool on how I can repay my debt to the Perl
225 Community, and as a practical module that is useful. I'm thrilled to be
226 able to offer this bit of code. So, if you have suggestions, bug
227 reports, or feature requests, please let me know and I'll do my best to
228 make this a better module.
229
231 Mike Wong <mike_w3@pacbell.net>
232 XML::Dumper is free software. You can redistribute it and/or modify it
234 under the same terms as Perl itself.
235
237 Jonathan Eisenzopf <eisen@pobox.com>
238
240 perl(1) Compress::Zlib(3) XML::Parser(3) Data::DumpXML(3)
241perl v5.36.0 2023-01-20 Dumper(3)