NAME¶
XML::Writer - Perl extension for writing XML documents.
SYNOPSIS¶
use XML::Writer;
use IO::File;
my $output = IO::File->new(">output.xml");
my $writer = XML::Writer->new(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 = XML::Writer->new(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, or any blessed object that has a
print() method; 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).
If the string self is passed, the output will be captured internally
by the object, and can be accessed via the "to_string()" method,
or by calling the object in a string context.
my $writer = XML::Writer->new( OUTPUT => 'self' );
$writer->dataElement( hello => 'world' );
print $writer->to_string; # outputs <hello>world</hello>
print "$writer"; # ditto
- 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 = XML::Writer->new(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 $writer = XML::Writer->new(NAMESPACES => 1,
PREFIX_MAP => {$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 or white space; if this parameter is present, it
represents the indent step for elements in data mode (it will be ignored
when not in data mode). If it is white space it will be repeated for each
level of indentation.
- ENCODING
- A character encoding to use for the output; 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. All
character data should be passed as Unicode strings when an encoding is
set.
- CHECK_PRINT
- A true or false value; if this parameter is present and its value is true,
all prints to the underlying output will be checked for success. Failures
will cause a croak rather than being ignored.
- 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:
$writer->end();
If OUTPUT as been set to self, "end()" will return
the generated document as well.
- xmlDecl([$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 = XML::Writer->new(OUTPUT => $output, UNSAFE => 1);
PRINTING OUTPUT¶
If
OUTPUT has been set to
self and the object has been called in a
string context, it'll return the xml document.
- to_string
- If OUTPUT has been set to self, calls an implicit
"end()" on the document and prints it. Dies if OUTPUT has
been set to anything else.
AUTHOR¶
David Megginson <david@megginson.com>
COPYRIGHT AND LICENSE¶
Copyright (c) 1999 by Megginson Technologies.
Copyright (c) 2003 Ed Avis <ed@membled.com>
Copyright (c) 2004-2010 Joseph Walton <joe@kafsemo.org>
Redistribution and use in source and compiled forms, with or without
modification, are permitted under any circumstances. No warranty.
SEE ALSO¶
XML::Parser