Writer(3) User Contributed Perl Documentation Writer(3)
NAME
XML::Writer - Perl extension for writing XML documents.
SYNOPSIS
use XML::Writer;
use IO::File;
my $output = new IO::File(">output.xml");
my $writer = new XML::Writer(OUTPUT => $output);
$writer->startTag("greeting",
"class" => "simple");
$writer->characters("Hello, world!");
$writer->endTag("greeting");
$writer->end();
$output->close();
DESCRIPTION
XML::Writer is a helper module for Perl programs that write an XML document. The module handles all
escaping for attribute values and character data and constructs different types of markup, such as
tags, comments, and processing instructions.
By default, the module performs several well-formedness checks to catch errors during output. This
behaviour can be extremely useful during development and debugging, but it can be turned off for
production-grade code.
The module can operate either in regular mode in or Namespace processing mode. In Namespace mode,
the module will generate Namespace Declarations itself, and will perform additional checks on the
output.
Additional support is available for a simplified data mode with no mixed content: newlines are
automatically inserted around elements and elements can optionally be indented based as their nesting
level.
METHODS
Writing XML
new([$params])
Create a new XML::Writer object:
my $writer = new XML::Writer(OUTPUT => $output, NEWLINES => 1);
Arguments are an anonymous hash array of parameters:
OUTPUT
An object blessed into IO::Handle or one of its subclasses (such as IO::File), or a reference
to a string; if this parameter is not present, the module will write to standard output. If a
string reference is passed, it will capture the generated XML (as a string; to get bytes use
the "Encode" module).
NAMESPACES
A true (1) or false (0, undef) value; if this parameter is present and its value is true,
then the module will accept two-member array reference in the place of element and attribute
names, as in the following example:
my $rdfns = "http://www.w3.org/1999/02/22-rdf-syntax-ns#";
my $writer = new XML::Writer(NAMESPACES => 1);
$writer->startTag([$rdfns, "Description"]);
The first member of the array is a namespace URI, and the second part is the local part of a
qualified name. The module will automatically generate appropriate namespace declarations
and will replace the URI part with a prefix.
PREFIX_MAP
A hash reference; if this parameter is present and the module is performing namespace
processing (see the NAMESPACES parameter), then the module will use this hash to look up
preferred prefixes for namespace URIs:
my $rdfns = "http://www.w3.org/1999/02/22-rdf-syntax-ns#";
my $writer = new XML::Writer(NAMESPACES => 1,
PREFIX_MAP => {$rdfns => 'rdf'});
The keys in the hash table are namespace URIs, and the values are the associated prefixes.
If there is not a preferred prefix for the namespace URI in this hash, then the module will
automatically generate prefixes of the form "__NS1", "__NS2", etc.
To set the default namespace, use '' for the prefix.
FORCED_NS_DECLS
An array reference; if this parameter is present, the document element will contain
declarations for all the given namespace URIs. Declaring namespaces in advance is
particularly useful when a large number of elements from a namespace are siblings, but don't
share a direct ancestor from the same namespace.
NEWLINES
A true or false value; if this parameter is present and its value is true, then the module
will insert an extra newline before the closing delimiter of start, end, and empty tags to
guarantee that the document does not end up as a single, long line. If the parameter is not
present, the module will not insert the newlines.
UNSAFE
A true or false value; if this parameter is present and its value is true, then the module
will skip most well-formedness error checking. If the parameter is not present, the module
will perform the well-formedness error checking by default. Turn off error checking at your
own risk!
DATA_MODE
A true or false value; if this parameter is present and its value is true, then the module
will enter a special data mode, inserting newlines automatically around elements and (unless
UNSAFE is also specified) reporting an error if any element has both characters and elements
as content.
DATA_INDENT
A numeric value; if this parameter is present, it represents the indent step for elements in
data mode (it will be ignored when not in data mode).
ENCODING
A character encoding; currently this must be one of 'utf-8' or 'us-ascii'. If present, it
will be used for the underlying character encoding and as the default in the XML declaration.
end()
Finish creating an XML document. This method will check that the document has exactly one
document element, and that all start tags are closed:
$writer->end();
xmlDecl([$encoding, $standalone])
Add an XML declaration to the beginning of an XML document. The version will always be "1.0".
If you provide a non-null encoding or standalone argument, its value will appear in the
declaration (any non-null value for standalone except 'no' will automatically be converted to
'yes'). If not given here, the encoding will be taken from the ENCODING argument. Pass the empty
string to suppress this behaviour.
$writer->xmlDecl("UTF-8");
doctype($name, [$publicId, $systemId])
Add a DOCTYPE declaration to an XML document. The declaration must appear before the beginning
of the root element. If you provide a publicId, you must provide a systemId as well, but you may
provide just a system ID by passing 'undef' for the publicId.
$writer->doctype("html");
comment($text)
Add a comment to an XML document. If the comment appears outside the document element (either
before the first start tag or after the last end tag), the module will add a carriage return
after it to improve readability. In data mode, comments will be treated as empty tags:
$writer->comment("This is a comment");
pi($target [, $data])
Add a processing instruction to an XML document:
$writer->pi('xml-stylesheet', 'href="style.css" type="text/css"');
If the processing instruction appears outside the document element (either before the first start
tag or after the last end tag), the module will add a carriage return after it to improve
readability.
The $target argument must be a single XML name. If you provide the $data argument, the module
will insert its contents following the $target argument, separated by a single space.
startTag($name [, $aname1 => $value1, ...])
Add a start tag to an XML document. Any arguments after the element name are assumed to be
name/value pairs for attributes: the module will escape all '&', '<', '>', and '"' characters in
the attribute values using the predefined XML entities:
$writer->startTag('doc', 'version' => '1.0',
'status' => 'draft',
'topic' => 'AT&T');
All start tags must eventually have matching end tags.
emptyTag($name [, $aname1 => $value1, ...])
Add an empty tag to an XML document. Any arguments after the element name are assumed to be
name/value pairs for attributes (see startTag() for details):
$writer->emptyTag('img', 'src' => 'portrait.jpg',
'alt' => 'Portrait of Emma.');
endTag([$name])
Add an end tag to an XML document. The end tag must match the closest open start tag, and there
must be a matching and properly-nested end tag for every start tag:
$writer->endTag('doc');
If the $name argument is omitted, then the module will automatically supply the name of the
currently open element:
$writer->startTag('p');
$writer->endTag();
dataElement($name, $data [, $aname1 => $value1, ...])
Print an entire element containing only character data. This is equivalent to
$writer->startTag($name [, $aname1 => $value1, ...]);
$writer->characters($data);
$writer->endTag($name);
characters($data)
Add character data to an XML document. All '<', '>', and '&' characters in the $data argument
will automatically be escaped using the predefined XML entities:
$writer->characters("Here is the formula: ");
$writer->characters("a < 100 && a > 5");
You may invoke this method only within the document element (i.e. after the first start tag and
before the last end tag).
In data mode, you must not use this method to add whitespace between elements.
raw($data)
Print data completely unquoted and unchecked to the XML document. For example "raw('<')" will
print a literal < character. This necessarily bypasses all well-formedness checking, and is
therefore only available in unsafe mode.
This can sometimes be useful for printing entities which are defined for your XML format but the
module doesn't know about, for example for XHTML.
cdata($data)
As "characters()" but writes the data quoted in a CDATA section, that is, between <![CDATA[ and
]]>. If the data to be written itself contains ]]>, it will be written as several consecutive
CDATA sections.
cdataElement($name, $data [, $aname1 => $value1, ...])
As "dataElement()" but the element content is written as one or more CDATA sections (see
"cdata()").
setOutput($output)
Set the current output destination, as in the OUTPUT parameter for the constructor.
getOutput()
Return the current output destination, as in the OUTPUT parameter for the constructor.
setDataMode($mode)
Enable or disable data mode, as in the DATA_MODE parameter for the constructor.
getDataMode()
Return the current data mode, as in the DATA_MODE parameter for the constructor.
setDataIndent($step)
Set the indent step for data mode, as in the DATA_INDENT parameter for the constructor.
getDataIndent()
Return the indent step for data mode, as in the DATA_INDENT parameter for the constructor.
Querying XML
in_element($name)
Return a true value if the most recent open element matches $name:
if ($writer->in_element('dl')) {
$writer->startTag('dt');
} else {
$writer->startTag('li');
}
within_element($name)
Return a true value if any open element matches $name:
if ($writer->within_element('body')) {
$writer->startTag('h1');
} else {
$writer->startTag('title');
}
current_element()
Return the name of the currently open element:
my $name = $writer->current_element();
This is the equivalent of
my $name = $writer->ancestor(0);
ancestor($n)
Return the name of the nth ancestor, where $n=0 for the current open element.
Additional Namespace Support
As of 0.510, these methods may be used while writing a document.
addPrefix($uri, $prefix)
Add a preferred mapping between a Namespace URI and a prefix. See also the PREFIX_MAP
constructor parameter.
To set the default namespace, omit the $prefix parameter or set it to ''.
removePrefix($uri)
Remove a preferred mapping between a Namespace URI and a prefix.
forceNSDecl($uri)
Indicate that a namespace declaration for this URI should be included with the next element to be
started.
ERROR REPORTING
With the default settings, the XML::Writer module can detect several basic XML well-formedness
errors:
Lack of a (top-level) document element, or multiple document elements.
Unclosed start tags.
Misplaced delimiters in the contents of processing instructions or comments.
Misplaced or duplicate XML declaration(s).
Misplaced or duplicate DOCTYPE declaration(s).
Mismatch between the document type name in the DOCTYPE declaration and the name of the document
element.
Mismatched start and end tags.
Attempts to insert character data outside the document element.
Duplicate attributes with the same name.
During Namespace processing, the module can detect the following additional errors:
Attempts to use PI targets or element or attribute names containing a colon.
Attempts to use attributes with names beginning "xmlns".
To ensure full error detection, a program must also invoke the end method when it has finished
writing a document:
$writer->startTag('greeting');
$writer->characters("Hello, world!");
$writer->endTag('greeting');
$writer->end();
This error reporting can catch many hidden bugs in Perl programs that create XML documents; however,
if necessary, it can be turned off by providing an UNSAFE parameter:
my $writer = new XML::Writer(OUTPUT => $output, UNSAFE => 1);
AUTHOR
David Megginson <david@megginson.com>
COPYRIGHT
Copyright 1999, 2000 David Megginson <david@megginson.com>
Copyright 2004, 2005 Joseph Walton <joe@kafsemo.org>
SEE ALSO
XML::Parser
perl v5.8.8 2006-09-01 Writer(3)
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