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OpenSolaris 2009.06 - man page for xml::simple (opensolaris section 3)

XML::Simple(3)		       User Contributed Perl Documentation		   XML::Simple(3)

       XML::Simple - Easy API to maintain XML (esp config files)

	   use XML::Simple;

	   my $ref = XMLin([<xml file or string>] [, <options>]);

	   my $xml = XMLout($hashref [, <options>]);

       Or the object oriented way:

	   require XML::Simple;

	   my $xs = XML::Simple->new(options);

	   my $ref = $xs->XMLin([<xml file or string>] [, <options>]);

	   my $xml = $xs->XMLout($hashref [, <options>]);

       (or see "SAX SUPPORT" for 'the SAX way').

       To catch common errors:

	   use XML::Simple qw(:strict);

       (see "STRICT MODE" for more details).

       Say you have a script called foo and a file of configuration options called foo.xml con-
       taining this:

	 <config logdir="/var/log/foo/" debugfile="/tmp/foo.debug">
	   <server name="sahara" osname="solaris" osversion="2.6">
	   <server name="gobi" osname="irix" osversion="6.5">
	   <server name="kalahari" osname="linux" osversion="2.0.34">

       The following lines of code in foo:

	 use XML::Simple;

	 my $config = XMLin();

       will 'slurp' the configuration options into the hashref $config (because no arguments are
       passed to "XMLin()" the name and location of the XML file will be inferred from name and
       location of the script).  You can dump out the contents of the hashref using Data::Dumper:

	 use Data::Dumper;

	 print Dumper($config);

       which will produce something like this (formatting has been adjusted for brevity):

	     'logdir'	     => '/var/log/foo/',
	     'debugfile'     => '/tmp/foo.debug',
	     'server'	     => {
		 'sahara'	 => {
		     'osversion'     => '2.6',
		     'osname'	     => 'solaris',
		     'address'	     => [ '', '' ]
		 'gobi' 	 => {
		     'osversion'     => '6.5',
		     'osname'	     => 'irix',
		     'address'	     => ''
		 'kalahari'	 => {
		     'osversion'     => '2.0.34',
		     'osname'	     => 'linux',
		     'address'	     => [ '', '' ]

       Your script could then access the name of the log directory like this:

	 print $config->{logdir};

       similarly, the second address on the server 'kalahari' could be referenced as:

	 print $config->{server}->{kalahari}->{address}->[1];

       What could be simpler?  (Rhetorical).

       For simple requirements, that's really all there is to it.  If you want to store your XML
       in a different directory or file, or pass it in as a string or even pass it in via some
       derivative of an IO::Handle, you'll need to check out "OPTIONS".  If you want to turn off
       or tweak the array folding feature (that neat little transformation that produced $con-
       fig->{server}) you'll find options for that as well.

       If you want to generate XML (for example to write a modified version of $config back out
       as XML), check out "XMLout()".

       If your needs are not so simple, this may not be the module for you.  In that case, you
       might want to read "WHERE TO FROM HERE?".

       The XML::Simple module provides a simple API layer on top of an underlying XML parsing
       module (either XML::Parser or one of the SAX2 parser modules).  Two functions are
       exported: "XMLin()" and "XMLout()".  Note: you can explicity request the lower case ver-
       sions of the function names: "xml_in()" and "xml_out()".

       The simplest approach is to call these two functions directly, but an optional object ori-
       ented interface (see "OPTIONAL OO INTERFACE" below) allows them to be called as methods of
       an XML::Simple object.  The object interface can also be used at either end of a SAX pipe-


       Parses XML formatted data and returns a reference to a data structure which contains the
       same information in a more readily accessible form.  (Skip down to "EXAMPLES" below, for
       more sample code).

       "XMLin()" accepts an optional XML specifier followed by zero or more 'name => value'
       option pairs.  The XML specifier can be one of the following:

       A filename
	   If the filename contains no directory components "XMLin()" will look for the file in
	   each directory in the SearchPath (see "OPTIONS" below) or in the current directory if
	   the SearchPath option is not defined.  eg:

	     $ref = XMLin('/etc/params.xml');

	   Note, the filename '-' can be used to parse from STDIN.

	   If there is no XML specifier, "XMLin()" will check the script directory and each of
	   the SearchPath directories for a file with the same name as the script but with the
	   extension '.xml'.  Note: if you wish to specify options, you must specify the value
	   'undef'.  eg:

	     $ref = XMLin(undef, ForceArray => 1);

       A string of XML
	   A string containing XML (recognised by the presence of '<' and '>' characters) will be
	   parsed directly.  eg:

	     $ref = XMLin('<opt username="bob" password="flurp" />');

       An IO::Handle object
	   An IO::Handle object will be read to EOF and its contents parsed. eg:

	     $fh = IO::File->new('/etc/params.xml');
	     $ref = XMLin($fh);


       Takes a data structure (generally a hashref) and returns an XML encoding of that struc-
       ture.  If the resulting XML is parsed using "XMLin()", it should return a data structure
       equivalent to the original (see caveats below).

       The "XMLout()" function can also be used to output the XML as SAX events see the "Handler"
       option and "SAX SUPPORT" for more details).

       When translating hashes to XML, hash keys which have a leading '-' will be silently
       skipped.  This is the approved method for marking elements of a data structure which
       should be ignored by "XMLout".  (Note: If these items were not skipped the key names would
       be emitted as element or attribute names with a leading '-' which would not be valid XML).


       Some care is required in creating data structures which will be passed to "XMLout()".
       Hash keys from the data structure will be encoded as either XML element names or attribute
       names.  Therefore, you should use hash key names which conform to the relatively strict
       XML naming rules:

       Names in XML must begin with a letter.  The remaining characters may be letters, digits,
       hyphens (-), underscores (_) or full stops (.).	It is also allowable to include one colon
       (:) in an element name but this should only be used when working with namespaces
       (XML::Simple can only usefully work with namespaces when teamed with a SAX Parser).

       You can use other punctuation characters in hash values (just not in hash keys) however
       XML::Simple does not support dumping binary data.

       If you break these rules, the current implementation of "XMLout()" will simply emit non-
       compliant XML which will be rejected if you try to read it back in.  (A later version of
       XML::Simple might take a more proactive approach).

       Note also that although you can nest hashes and arrays to arbitrary levels, circular data
       structures are not supported and will cause "XMLout()" to die.

       If you wish to 'round-trip' arbitrary data structures from Perl to XML and back to Perl,
       then you should probably disable array folding (using the KeyAttr option) both with
       "XMLout()" and with "XMLin()".  If you still don't get the expected results, you may pre-
       fer to use XML::Dumper which is designed for exactly that purpose.

       Refer to "WHERE TO FROM HERE?" if "XMLout()" is too simple for your needs.

       XML::Simple supports a number of options (in fact as each release of XML::Simple adds more
       options, the module's claim to the name 'Simple' becomes increasingly tenuous).	If you
       find yourself repeatedly having to specify the same options, you might like to investigate

       If you can't be bothered reading the documentation, refer to "STRICT MODE" to automati-
       cally catch common mistakes.

       Because there are so many options, it's hard for new users to know which ones are impor-
       tant, so here are the two you really need to know about:

       o   check out "ForceArray" because you'll almost certainly want to turn it on

       o   make sure you know what the "KeyAttr" option does and what its default value is
	   because it may surprise you otherwise (note in particular that 'KeyAttr' affects both
	   "XMLin" and "XMLout")

       The option name headings below have a trailing 'comment' - a hash followed by two pieces
       of metadata:

       o   Options are marked with 'in' if they are recognised by "XMLin()" and 'out' if they are
	   recognised by "XMLout()".

       o   Each option is also flagged to indicate whether it is:

	    'important'   - don't use the module until you understand this one
	    'handy'	  - you can skip this on the first time through
	    'advanced'	  - you can skip this on the second time through
	    'SAX only'	  - don't worry about this unless you're using SAX (or
			    alternatively if you need this, you also need SAX)
	    'seldom used' - you'll probably never use this unless you were the
			    person that requested the feature

       The options are listed alphabetically:

       Note: option names are no longer case sensitive so you can use the mixed case versions
       shown here; all lower case as required by versions 2.03 and earlier; or you can add under-
       scores between the words (eg: key_attr).

       AttrIndent => 1 # out - handy

       When you are using "XMLout()", enable this option to have attributes printed one-per-line
       with sensible indentation rather than all on one line.

       Cache => [ cache schemes ] # in - advanced

       Because loading the XML::Parser module and parsing an XML file can consume a significant
       number of CPU cycles, it is often desirable to cache the output of "XMLin()" for later re-

       When parsing from a named file, XML::Simple supports a number of caching schemes.  The
       'Cache' option may be used to specify one or more schemes (using an anonymous array).
       Each scheme will be tried in turn in the hope of finding a cached pre-parsed representa-
       tion of the XML file.  If no cached copy is found, the file will be parsed and the first
       cache scheme in the list will be used to save a copy of the results.  The following cache
       schemes have been implemented:

	   Utilises Storable.pm to read/write a cache file with the same name as the XML file but
	   with the extension .stor

	   When a file is first parsed, a copy of the resulting data structure is retained in
	   memory in the XML::Simple module's namespace.  Subsequent calls to parse the same file
	   will return a reference to this structure.  This cached version will persist only for
	   the life of the Perl interpreter (which in the case of mod_perl for example, may be
	   some significant time).

	   Because each caller receives a reference to the same data structure, a change made by
	   one caller will be visible to all.  For this reason, the reference returned should be
	   treated as read-only.

	   This scheme works identically to 'memshare' (above) except that each caller receives a
	   reference to a new data structure which is a copy of the cached version.  Copying the
	   data structure will add a little processing overhead, therefore this scheme should
	   only be used where the caller intends to modify the data structure (or wishes to pro-
	   tect itself from others who might).	This scheme uses Storable.pm to perform the copy.

       Warning! The memory-based caching schemes compare the timestamp on the file to the time
       when it was last parsed.  If the file is stored on an NFS filesystem (or other network
       share) and the clock on the file server is not exactly synchronised with the clock where
       your script is run, updates to the source XML file may appear to be ignored.

       ContentKey => 'keyname' # in+out - seldom used

       When text content is parsed to a hash value, this option let's you specify a name for the
       hash key to override the default 'content'.  So for example:

	 XMLin('<opt one="1">Text</opt>', ContentKey => 'text')

       will parse to:

	 { 'one' => 1, 'text' => 'Text' }

       instead of:

	 { 'one' => 1, 'content' => 'Text' }

       "XMLout()" will also honour the value of this option when converting a hashref to XML.

       You can also prefix your selected key name with a '-' character to have "XMLin()" try a
       little harder to eliminate unnecessary 'content' keys after array folding.  For example:

	   '<opt><item name="one">First</item><item name="two">Second</item></opt>',
	   KeyAttr => {item => 'name'},
	   ForceArray => [ 'item' ],
	   ContentKey => '-content'

       will parse to:

	   'item' => {
	     'one' =>  'First'
	     'two' =>  'Second'

       rather than this (without the '-'):

	   'item' => {
	     'one' => { 'content' => 'First' }
	     'two' => { 'content' => 'Second' }

       DataHandler => code_ref # in - SAX only

       When you use an XML::Simple object as a SAX handler, it will return a 'simple tree' data
       structure in the same format as "XMLin()" would return.	If this option is set (to a sub-
       routine reference), then when the tree is built the subroutine will be called and passed
       two arguments: a reference to the XML::Simple object and a reference to the data tree.
       The return value from the subroutine will be returned to the SAX driver.  (See "SAX SUP-
       PORT" for more details).

       ForceArray => 1 # in - important

       This option should be set to '1' to force nested elements to be represented as arrays even
       when there is only one.	Eg, with ForceArray enabled, this XML:


       would parse to this:

	     'name' => [

       instead of this (the default):

	     'name' => 'value'

       This option is especially useful if the data structure is likely to be written back out as
       XML and the default behaviour of rolling single nested elements up into attributes is not

       If you are using the array folding feature, you should almost certainly enable this
       option.	If you do not, single nested elements will not be parsed to arrays and therefore
       will not be candidates for folding to a hash.  (Given that the default value of 'KeyAttr'
       enables array folding, the default value of this option should probably also have been
       enabled too - sorry).

       ForceArray => [ names ] # in - important

       This alternative (and preferred) form of the 'ForceArray' option allows you to specify a
       list of element names which should always be forced into an array representation, rather
       than the 'all or nothing' approach above.

       It is also possible (since version 2.05) to include compiled regular expressions in the
       list - any element names which match the pattern will be forced to arrays.  If the list
       contains only a single regex, then it is not necessary to enclose it in an arrayref.  Eg:

	 ForceArray => qr/_list$/

       ForceContent => 1 # in - seldom used

       When "XMLin()" parses elements which have text content as well as attributes, the text
       content must be represented as a hash value rather than a simple scalar.  This option
       allows you to force text content to always parse to a hash value even when there are no
       attributes.  So for example:

	 XMLin('<opt><x>text1</x><y a="2">text2</y></opt>', ForceContent => 1)

       will parse to:

	   'x' => {	      'content' => 'text1' },
	   'y' => { 'a' => 2, 'content' => 'text2' }

       instead of:

	   'x' => 'text1',
	   'y' => { 'a' => 2, 'content' => 'text2' }

       GroupTags => { grouping tag => grouped tag } # in+out - handy

       You can use this option to eliminate extra levels of indirection in your Perl data struc-
       ture.  For example this XML:


       Would normally be read into a structure like this:

	   searchpath => {
			   dir => [ '/usr/bin', '/usr/local/bin', '/usr/X11/bin' ]

       But when read in with the appropriate value for 'GroupTags':

	 my $opt = XMLin($xml, GroupTags => { searchpath => 'dir' });

       It will return this simpler structure:

	   searchpath => [ '/usr/bin', '/usr/local/bin', '/usr/X11/bin' ]

       The grouping element ("<searchpath>" in the example) must not contain any attributes or
       elements other than the grouped element.

       You can specify multiple 'grouping element' to 'grouped element' mappings in the same
       hashref.  If this option is combined with "KeyAttr", the array folding will occur first
       and then the grouped element names will be eliminated.

       "XMLout" will also use the grouptag mappings to re-introduce the tags around the grouped
       elements.  Beware though that this will occur in all places that the 'grouping tag' name
       occurs - you probably don't want to use the same name for elements as well as attributes.

       Handler => object_ref # out - SAX only

       Use the 'Handler' option to have "XMLout()" generate SAX events rather than returning a
       string of XML.  For more details see "SAX SUPPORT" below.

       Note: the current implementation of this option generates a string of XML and uses a SAX
       parser to translate it into SAX events.	The normal encoding rules apply here - your data
       must be UTF8 encoded unless you specify an alternative encoding via the 'XMLDecl' option;
       and by the time the data reaches the handler object, it will be in UTF8 form regardless of
       the encoding you supply.  A future implementation of this option may generate the events

       KeepRoot => 1 # in+out - handy

       In its attempt to return a data structure free of superfluous detail and unnecessary lev-
       els of indirection, "XMLin()" normally discards the root element name.  Setting the 'Keep-
       Root' option to '1' will cause the root element name to be retained.  So after executing
       this code:

	 $config = XMLin('<config tempdir="/tmp" />', KeepRoot => 1)

       You'll be able to reference the tempdir as "$config->{config}->{tempdir}" instead of the
       default "$config->{tempdir}".

       Similarly, setting the 'KeepRoot' option to '1' will tell "XMLout()" that the data struc-
       ture already contains a root element name and it is not necessary to add another.

       KeyAttr => [ list ] # in+out - important

       This option controls the 'array folding' feature which translates nested elements from an
       array to a hash.  It also controls the 'unfolding' of hashes to arrays.

       For example, this XML:

	     <user login="grep" fullname="Gary R Epstein" />
	     <user login="stty" fullname="Simon T Tyson" />

       would, by default, parse to this:

	     'user' => [
			   'login' => 'grep',
			   'fullname' => 'Gary R Epstein'
			   'login' => 'stty',
			   'fullname' => 'Simon T Tyson'

       If the option 'KeyAttr => "login"' were used to specify that the 'login' attribute is a
       key, the same XML would parse to:

	     'user' => {
			 'stty' => {
				     'fullname' => 'Simon T Tyson'
			 'grep' => {
				     'fullname' => 'Gary R Epstein'

       The key attribute names should be supplied in an arrayref if there is more than one.
       "XMLin()" will attempt to match attribute names in the order supplied.  "XMLout()" will
       use the first attribute name supplied when 'unfolding' a hash into an array.

       Note 1: The default value for 'KeyAttr' is ['name', 'key', 'id'].  If you do not want
       folding on input or unfolding on output you must setting this option to an empty list to
       disable the feature.

       Note 2: If you wish to use this option, you should also enable the "ForceArray" option.
       Without 'ForceArray', a single nested element will be rolled up into a scalar rather than
       an array and therefore will not be folded (since only arrays get folded).

       KeyAttr => { list } # in+out - important

       This alternative (and preferred) method of specifiying the key attributes allows more fine
       grained control over which elements are folded and on which attributes.	For example the
       option 'KeyAttr => { package => 'id' } will cause any package elements to be folded on the
       'id' attribute.	No other elements which have an 'id' attribute will be folded at all.

       Note: "XMLin()" will generate a warning (or a fatal error in "STRICT MODE") if this syntax
       is used and an element which does not have the specified key attribute is encountered (eg:
       a 'package' element without an 'id' attribute, to use the example above).  Warnings will
       only be generated if -w is in force.

       Two further variations are made possible by prefixing a '+' or a '-' character to the
       attribute name:

       The option 'KeyAttr => { user => "+login" }' will cause this XML:

	     <user login="grep" fullname="Gary R Epstein" />
	     <user login="stty" fullname="Simon T Tyson" />

       to parse to this data structure:

	     'user' => {
			 'stty' => {
				     'fullname' => 'Simon T Tyson',
				     'login'	=> 'stty'
			 'grep' => {
				     'fullname' => 'Gary R Epstein',
				     'login'	=> 'grep'

       The '+' indicates that the value of the key attribute should be copied rather than moved
       to the folded hash key.

       A '-' prefix would produce this result:

	     'user' => {
			 'stty' => {
				     'fullname' => 'Simon T Tyson',
				     '-login'	 => 'stty'
			 'grep' => {
				     'fullname' => 'Gary R Epstein',
				     '-login'	 => 'grep'

       As described earlier, "XMLout" will ignore hash keys starting with a '-'.

       NoAttr => 1 # in+out - handy

       When used with "XMLout()", the generated XML will contain no attributes.  All hash
       key/values will be represented as nested elements instead.

       When used with "XMLin()", any attributes in the XML will be ignored.

       NoEscape => 1 # out - seldom used

       By default, "XMLout()" will translate the characters '<', '>', '&' and '"' to '&lt;',
       '&gt;', '&amp;' and '&quot' respectively.  Use this option to suppress escaping (presum-
       ably because you've already escaped the data in some more sophisticated manner).

       NoIndent => 1 # out - seldom used

       Set this option to 1 to disable "XMLout()"'s default 'pretty printing' mode.  With this
       option enabled, the XML output will all be on one line (unless there are newlines in the
       data) - this may be easier for downstream processing.

       NoSort => 1 # out - seldom used

       Newer versions of XML::Simple sort elements and attributes alphabetically (*), by default.
       Enable this option to suppress the sorting - possibly for backwards compatibility.

       * Actually, sorting is alphabetical but 'key' attribute or element names (as in 'KeyAttr')
       sort first.  Also, when a hash of hashes is 'unfolded', the elements are sorted alphabeti-
       cally by the value of the key field.

       NormaliseSpace => 0 | 1 | 2 # in - handy

       This option controls how whitespace in text content is handled.	Recognised values for the
       option are:

       o   0 = (default) whitespace is passed through unaltered (except of course for the normal-
	   isation of whitespace in attribute values which is mandated by the XML recommendation)

       o   1 = whitespace is normalised in any value used as a hash key (normalising means remov-
	   ing leading and trailing whitespace and collapsing sequences of whitespace characters
	   to a single space)

       o   2 = whitespace is normalised in all text content

       Note: you can spell this option with a 'z' if that is more natural for you.

       NSExpand => 1 # in+out handy - SAX only

       This option controls namespace expansion - the translation of element and attribute names
       of the form 'prefix:name' to '{uri}name'.  For example the element name 'xsl:template'
       might be expanded to: '{http://www.w3.org/1999/XSL/Transform}template'.

       By default, "XMLin()" will return element names and attribute names exactly as they appear
       in the XML.  Setting this option to 1 will cause all element and attribute names to be
       expanded to include their namespace prefix.

       Note: You must be using a SAX parser for this option to work (ie: it does not work with

       This option also controls whether "XMLout()" performs the reverse translation from
       '{uri}name' back to 'prefix:name'.  The default is no translation.  If your data contains
       expanded names, you should set this option to 1 otherwise "XMLout" will emit XML which is
       not well formed.

       Note: You must have the XML::NamespaceSupport module installed if you want "XMLout()" to
       translate URIs back to prefixes.

       NumericEscape => 0 | 1 | 2 # out - handy

       Use this option to have 'high' (non-ASCII) characters in your Perl data structure con-
       verted to numeric entities (eg: &#8364;) in the XML output.  Three levels are possible:

       0 - default: no numeric escaping (OK if you're writing out UTF8)

       1 - only characters above 0xFF are escaped (ie: characters in the 0x80-FF range are not
       escaped), possibly useful with ISO8859-1 output

       2 - all characters above 0x7F are escaped (good for plain ASCII output)

       OutputFile => <file specifier> # out - handy

       The default behaviour of "XMLout()" is to return the XML as a string.  If you wish to
       write the XML to a file, simply supply the filename using the 'OutputFile' option.

       This option also accepts an IO handle object - especially useful in Perl 5.8.0 and later
       for output using an encoding other than UTF-8, eg:

	 open my $fh, '>:encoding(iso-8859-1)', $path or die "open($path): $!";
	 XMLout($ref, OutputFile => $fh);

       Note, XML::Simple does not require that the object you pass in to the OutputFile option
       inherits from IO::Handle - it simply assumes the object supports a "print" method.

       ParserOpts => [ XML::Parser Options ] # in - don't use this

       Note: This option is now officially deprecated.	If you find it useful, email the author
       with an example of what you use it for.	Do not use this option to set the ProtocolEncod-
       ing, that's just plain wrong - fix the XML.

       This option allows you to pass parameters to the constructor of the underlying XML::Parser
       object (which of course assumes you're not using SAX).

       RootName => 'string' # out - handy

       By default, when "XMLout()" generates XML, the root element will be named 'opt'.  This
       option allows you to specify an alternative name.

       Specifying either undef or the empty string for the RootName option will produce XML with
       no root elements.  In most cases the resulting XML fragment will not be 'well formed' and
       therefore could not be read back in by "XMLin()".  Nevertheless, the option has been found
       to be useful in certain circumstances.

       SearchPath => [ list ] # in - handy

       If you pass "XMLin()" a filename, but the filename include no directory component, you can
       use this option to specify which directories should be searched to locate the file.  You
       might use this option to search first in the user's home directory, then in a global
       directory such as /etc.

       If a filename is provided to "XMLin()" but SearchPath is not defined, the file is assumed
       to be in the current directory.

       If the first parameter to "XMLin()" is undefined, the default SearchPath will contain only
       the directory in which the script itself is located.  Otherwise the default SearchPath
       will be empty.

       SuppressEmpty => 1 | '' | undef # in+out - handy

       This option controls what "XMLin()" should do with empty elements (no attributes and no
       content).  The default behaviour is to represent them as empty hashes.  Setting this
       option to a true value (eg: 1) will cause empty elements to be skipped altogether.  Set-
       ting the option to 'undef' or the empty string will cause empty elements to be represented
       as the undefined value or the empty string respectively.  The latter two alternatives are
       a little easier to test for in your code than a hash with no keys.

       The option also controls what "XMLout()" does with undefined values.  Setting the option
       to undef causes undefined values to be output as empty elements (rather than empty
       attributes), it also suppresses the generation of warnings about undefined values.  Set-
       ting the option to a true value (eg: 1) causes undefined values to be skipped altogether
       on output.

       ValueAttr => [ names ] # in - handy

       Use this option to deal elements which always have a single attribute and no content.  Eg:

	   <colour value="red" />
	   <size   value="XXL" />

       Setting "ValueAttr => [ 'value' ]" will cause the above XML to parse to:

	   colour => 'red',
	   size   => 'XXL'

       instead of this (the default):

	   colour => { value => 'red' },
	   size   => { value => 'XXL' }

       Note: This form of the ValueAttr option is not compatible with "XMLout()" - since the
       attribute name is discarded at parse time, the original XML cannot be reconstructed.

       ValueAttr => { element => attribute, ... } # in+out - handy

       This (preferred) form of the ValueAttr option requires you to specify both the element and
       the attribute names.  This is not only safer, it also allows the original XML to be recon-
       structed by "XMLout()".

       Note: You probably don't want to use this option and the NoAttr option at the same time.

       Variables => { name => value } # in - handy

       This option allows variables in the XML to be expanded when the file is read.  (there is
       no facility for putting the variable names back if you regenerate XML using "XMLout").

       A 'variable' is any text of the form "${name}" which occurs in an attribute value or in
       the text content of an element.	If 'name' matches a key in the supplied hashref,
       "${name}" will be replaced with the corresponding value from the hashref.  If no matching
       key is found, the variable will not be replaced.  Names must match the regex: "[\w.]+"
       (ie: only 'word' characters and dots are allowed).

       VarAttr => 'attr_name' # in - handy

       In addition to the variables defined using "Variables", this option allows variables to be
       defined in the XML.  A variable definition consists of an element with an attribute called
       'attr_name' (the value of the "VarAttr" option).  The value of the attribute will be used
       as the variable name and the text content of the element will be used as the value.  A
       variable defined in this way will override a variable defined using the "Variables"
       option.	For example:

	 XMLin( '<opt>
		   <dir name="prefix">/usr/local/apache</dir>
		   <dir name="exec_prefix">${prefix}</dir>
		   <dir name="bindir">${exec_prefix}/bin</dir>
		VarAttr => 'name', ContentKey => '-content'

       produces the following data structure:

	   dir => {
		    prefix	=> '/usr/local/apache',
		    exec_prefix => '/usr/local/apache',
		    bindir	=> '/usr/local/apache/bin',

       XMLDecl => 1  or  XMLDecl => 'string'  # out - handy

       If you want the output from "XMLout()" to start with the optional XML declaration, simply
       set the option to '1'.  The default XML declaration is:

	       <?xml version='1.0' standalone='yes'?>

       If you want some other string (for example to declare an encoding value), set the value of
       this option to the complete string you require.

       The procedural interface is both simple and convenient however there are a couple of rea-
       sons why you might prefer to use the object oriented (OO) interface:

       o   to define a set of default values which should be used on all subsequent calls to
	   "XMLin()" or "XMLout()"

       o   to override methods in XML::Simple to provide customised behaviour

       The default values for the options described above are unlikely to suit everyone.  The OO
       interface allows you to effectively override XML::Simple's defaults with your preferred
       values.	It works like this:

       First create an XML::Simple parser object with your preferred defaults:

	 my $xs = XML::Simple->new(ForceArray => 1, KeepRoot => 1);

       then call "XMLin()" or "XMLout()" as a method of that object:

	 my $ref = $xs->XMLin($xml);
	 my $xml = $xs->XMLout($ref);

       You can also specify options when you make the method calls and these values will be
       merged with the values specified when the object was created.  Values specified in a
       method call take precedence.

       Note: when called as methods, the "XMLin()" and "XMLout()" routines may be called as
       "xml_in()" or "xml_out()".  The method names are aliased so the only difference is the

       Parsing Methods

       You can explicitly call one of the following methods rather than rely on the "xml_in()"
       method automatically determining whether the target to be parsed is a string, a file or a

	   Works exactly like the "xml_in()" method but assumes the first argument is a string of
	   XML (or a reference to a scalar containing a string of XML).

	   Works exactly like the "xml_in()" method but assumes the first argument is the name of
	   a file containing XML.

	   Works exactly like the "xml_in()" method but assumes the first argument is a filehan-
	   dle which can be read to get XML.

       Hook Methods

       You can make your own class which inherits from XML::Simple and overrides certain behav-
       iours.  The following methods may provide useful 'hooks' upon which to hang your modified
       behaviour.  You may find other undocumented methods by examining the source, but those may
       be subject to change in future releases.

       handle_options(direction, name => value ...)
	   This method will be called when one of the parsing methods or the "XMLout()" method is
	   called.  The initial argument will be a string (either 'in' or 'out') and the remain-
	   ing arguments will be name value pairs.

	   Calculates and returns the name of the file which should be parsed if no filename is
	   passed to "XMLin()" (default: "$0.xml").

       build_simple_tree(filename, string)
	   Called from "XMLin()" or any of the parsing methods.  Takes either a file name as the
	   first argument or "undef" followed by a 'string' as the second argument.  Returns a
	   simple tree data structure.	You could override this method to apply your own trans-
	   formations before the data structure is returned to the caller.

	   When the 'simple tree' data structure is being built, this method will be called to
	   create any required anonymous hashrefs.

       sorted_keys(name, hashref)
	   Called when "XMLout()" is translating a hashref to XML.  This routine returns a list
	   of hash keys in the order that the corresponding attributes/elements should appear in
	   the output.

	   Called from "XMLout()", takes a string and returns a copy of the string with XML char-
	   acter escaping rules applied.

	   Called from "escape_value()", to handle non-ASCII characters (depending on the value
	   of the NumericEscape option).

       copy_hash(hashref, extra_key => value, ...)
	   Called from "XMLout()", when 'unfolding' a hash of hashes into an array of hashes.
	   You might wish to override this method if you're using tied hashes and don't want them
	   to get untied.

       Cache Methods

       XML::Simple implements three caching schemes ('storable', 'memshare' and 'memcopy').  You
       can implement a custom caching scheme by implementing two methods - one for reading from
       the cache and one for writing to it.

       For example, you might implement a new 'dbm' scheme that stores cached data structures
       using the MLDBM module.	First, you would add a "cache_read_dbm()" method which accepted a
       filename for use as a lookup key and returned a data structure on success, or undef on
       failure.  Then, you would implement a "cache_read_dbm()" method which accepted a data
       structure and a filename.

       You would use this caching scheme by specifying the option:

	 Cache => [ 'dbm' ]

       If you import the XML::Simple routines like this:

	 use XML::Simple qw(:strict);

       the following common mistakes will be detected and treated as fatal errors

       o   Failing to explicitly set the "KeyAttr" option - if you can't be bothered reading
	   about this option, turn it off with: KeyAttr => [ ]

       o   Failing to explicitly set the "ForceArray" option - if you can't be bothered reading
	   about this option, set it to the safest mode with: ForceArray => 1

       o   Setting ForceArray to an array, but failing to list all the elements from the KeyAttr

       o   Data error - KeyAttr is set to say { part => 'partnum' } but the XML contains one or
	   more <part> elements without a 'partnum' attribute (or nested element).  Note: if
	   strict mode is not set but -w is, this condition triggers a warning.

       o   Data error - as above, but non-unique values are present in the key attribute (eg:
	   more than one <part> element with the same partnum).  This will also trigger a warning
	   if strict mode is not enabled.

       o   Data error - as above, but value of key attribute (eg: partnum) is not a scalar string
	   (due to nested elements etc).  This will also trigger a warning if strict mode is not

       From version 1.08_01, XML::Simple includes support for SAX (the Simple API for XML) -
       specifically SAX2.

       In a typical SAX application, an XML parser (or SAX 'driver') module generates SAX events
       (start of element, character data, end of element, etc) as it parses an XML document and a
       'handler' module processes the events to extract the required data.  This simple model
       allows for some interesting and powerful possibilities:

       o   Applications written to the SAX API can extract data from huge XML documents without
	   the memory overheads of a DOM or tree API.

       o   The SAX API allows for plug and play interchange of parser modules without having to
	   change your code to fit a new module's API.	A number of SAX parsers are available
	   with capabilities ranging from extreme portability to blazing performance.

       o   A SAX 'filter' module can implement both a handler interface for receiving data and a
	   generator interface for passing modified data on to a downstream handler.  Filters can
	   be chained together in 'pipelines'.

       o   One filter module might split a data stream to direct data to two or more downstream

       o   Generating SAX events is not the exclusive preserve of XML parsing modules.	For exam-
	   ple, a module might extract data from a relational database using DBI and pass it on
	   to a SAX pipeline for filtering and formatting.

       XML::Simple can operate at either end of a SAX pipeline.  For example, you can take a data
       structure in the form of a hashref and pass it into a SAX pipeline using the 'Handler'
       option on "XMLout()":

	 use XML::Simple;
	 use Some::SAX::Filter;
	 use XML::SAX::Writer;

	 my $ref = {
		      ....   # your data here

	 my $writer = XML::SAX::Writer->new();
	 my $filter = Some::SAX::Filter->new(Handler => $writer);
	 my $simple = XML::Simple->new(Handler => $filter);

       You can also put XML::Simple at the opposite end of the pipeline to take advantage of the
       simple 'tree' data structure once the relevant data has been isolated through filtering:

	 use XML::SAX;
	 use Some::SAX::Filter;
	 use XML::Simple;

	 my $simple = XML::Simple->new(ForceArray => 1, KeyAttr => ['partnum']);
	 my $filter = Some::SAX::Filter->new(Handler => $simple);
	 my $parser = XML::SAX::ParserFactory->parser(Handler => $filter);

	 my $ref = $parser->parse_uri('some_huge_file.xml');

	 print $ref->{part}->{'555-1234'};

       You can build a filter by using an XML::Simple object as a handler and setting its Data-
       Handler option to point to a routine which takes the resulting tree, modifies it and sends
       it off as SAX events to a downstream handler:

	 my $writer = XML::SAX::Writer->new();
	 my $filter = XML::Simple->new(
			DataHandler => sub {
					 my $simple = shift;
					 my $data = shift;

					 # Modify $data here

					 $simple->XMLout($data, Handler => $writer);
	 my $parser = XML::SAX::ParserFactory->parser(Handler => $filter);


       Note: In this last example, the 'Handler' option was specified in the call to "XMLout()"
       but it could also have been specified in the constructor.

       If you don't care which parser module XML::Simple uses then skip this section entirely (it
       looks more complicated than it really is).

       XML::Simple will default to using a SAX parser if one is available or XML::Parser if SAX
       is not available.

       You can dictate which parser module is used by setting either the environment variable
       'XML_SIMPLE_PREFERRED_PARSER' or the package variable $XML::Simple::PREFERRED_PARSER to
       contain the module name.  The following rules are used:

       o   The package variable takes precedence over the environment variable if both are
	   defined.  To force XML::Simple to ignore the environment settings and use its default
	   rules, you can set the package variable to an empty string.

       o   If the 'preferred parser' is set to the string 'XML::Parser', then XML::Parser will be
	   used (or "XMLin()" will die if XML::Parser is not installed).

       o   If the 'preferred parser' is set to some other value, then it is assumed to be the
	   name of a SAX parser module and is passed to XML::SAX::ParserFactory.  If XML::SAX is
	   not installed, or the requested parser module is not installed, then "XMLin()" will

       o   If the 'preferred parser' is not defined at all (the normal default state), an attempt
	   will be made to load XML::SAX.  If XML::SAX is installed, then a parser module will be
	   selected according to XML::SAX::ParserFactory's normal rules (which typically means
	   the last SAX parser installed).

       o   if the 'preferred parser' is not defined and XML::SAX is not installed, then
	   XML::Parser will be used.  "XMLin()" will die if XML::Parser is not installed.

       Note: The XML::SAX distribution includes an XML parser written entirely in Perl.  It is
       very portable but it is not very fast.  You should consider installing XML::LibXML or
       XML::SAX::Expat if they are available for your platform.

       The XML standard is very clear on the issue of non-compliant documents.	An error in pars-
       ing any single element (for example a missing end tag) must cause the whole document to be
       rejected.  XML::Simple will die with an appropriate message if it encounters a parsing

       If dying is not appropriate for your application, you should arrange to call "XMLin()" in
       an eval block and look for errors in $@.  eg:

	   my $config = eval { XMLin() };
	   PopUpMessage($@) if($@);

       Note, there is a common misconception that use of eval will significantly slow down a
       script.	While that may be true when the code being eval'd is in a string, it is not true
       of code like the sample above.

       When "XMLin()" reads the following very simple piece of XML:

	   <opt username="testuser" password="frodo"></opt>

       it returns the following data structure:

	     'username' => 'testuser',
	     'password' => 'frodo'

       The identical result could have been produced with this alternative XML:

	   <opt username="testuser" password="frodo" />

       Or this (although see 'ForceArray' option for variations):


       Repeated nested elements are represented as anonymous arrays:

	     <person firstname="Joe" lastname="Smith">
	     <person firstname="Bob" lastname="Smith">

	     'person' => [
			     'email' => [
			     'firstname' => 'Joe',
			     'lastname' => 'Smith'
			     'email' => 'bob@smith.com',
			     'firstname' => 'Bob',
			     'lastname' => 'Smith'

       Nested elements with a recognised key attribute are transformed (folded) from an array
       into a hash keyed on the value of that attribute (see the "KeyAttr" option):

	     <person key="jsmith" firstname="Joe" lastname="Smith" />
	     <person key="tsmith" firstname="Tom" lastname="Smith" />
	     <person key="jbloggs" firstname="Joe" lastname="Bloggs" />

	     'person' => {
			   'jbloggs' => {
					  'firstname' => 'Joe',
					  'lastname' => 'Bloggs'
			   'tsmith' => {
					 'firstname' => 'Tom',
					 'lastname' => 'Smith'
			   'jsmith' => {
					 'firstname' => 'Joe',
					 'lastname' => 'Smith'

       The <anon> tag can be used to form anonymous arrays:

	     <head><anon>Col 1</anon><anon>Col 2</anon><anon>Col 3</anon></head>

	     'head' => [
			 [ 'Col 1', 'Col 2', 'Col 3' ]
	     'data' => [
			 [ 'R1C1', 'R1C2', 'R1C3' ],
			 [ 'R2C1', 'R2C2', 'R2C3' ],
			 [ 'R3C1', 'R3C2', 'R3C3' ]

       Anonymous arrays can be nested to arbirtrary levels and as a special case, if the sur-
       rounding tags for an XML document contain only an anonymous array the arrayref will be
       returned directly rather than the usual hashref:

	     <anon><anon>Col 1</anon><anon>Col 2</anon></anon>

	     [ 'Col 1', 'Col 2' ],
	     [ 'R1C1', 'R1C2' ],
	     [ 'R2C1', 'R2C2' ]

       Elements which only contain text content will simply be represented as a scalar.  Where an
       element has both attributes and text content, the element will be represented as a hashref
       with the text content in the 'content' key (see the "ContentKey" option):

	   <two attr="value">second</two>

	   'one' => 'first',
	   'two' => { 'attr' => 'value', 'content' => 'second' }

       Mixed content (elements which contain both text content and nested elements) will be not
       be represented in a useful way - element order and significant whitespace will be lost.
       If you need to work with mixed content, then XML::Simple is not the right tool for your
       job - check out the next section.

       XML::Simple is able to present a simple API because it makes some assumptions on your
       behalf.	These include:

       o   You're not interested in text content consisting only of whitespace

       o   You don't mind that when things get slurped into a hash the order is lost

       o   You don't want fine-grained control of the formatting of generated XML

       o   You would never use a hash key that was not a legal XML element name

       o   You don't need help converting between different encodings

       In a serious XML project, you'll probably outgrow these assumptions fairly quickly.  This
       section of the document used to offer some advice on chosing a more powerful option.  That
       advice has now grown into the 'Perl-XML FAQ' document which you can find at:

       The advice in the FAQ boils down to a quick explanation of tree versus event based parsers
       and then recommends:

       For event based parsing, use SAX (do not set out to write any new code for XML::Parser's
       handler API - it is obselete).

       For tree-based parsing, you could choose between the 'Perlish' approach of XML::Twig and
       more standards based DOM implementations - preferably one with XPath support.

       XML::Simple requires either XML::Parser or XML::SAX.

       To generate documents with namespaces, XML::NamespaceSupport is required.

       The optional caching functions require Storable.

       Answers to Frequently Asked Questions about XML::Simple are bundled with this distribution
       as: XML::Simple::FAQ

       Copyright 1999-2004 Grant McLean <grantm@cpan.org>

       This library is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself.

perl v5.8.4				    2004-11-20				   XML::Simple(3)

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