XML::Bare - Minimal XML parser implemented via a C state engine




  use XML::Bare;
  my $ob = new XML::Bare( text => '<xml><name>Bob</name></xml>' );
  # Parse the xml into a hash tree
  my $root = $ob->parse();
  # Print the content of the name node
  print $root->{xml}->{name}->{value};
  # Load xml from a file ( assume same contents as first example )
  my $ob2 = new XML::Bare( file => 'test.xml' );
  my $root2 = $ob2->parse();
  $root2->{xml}->{name}->{value} = 'Tim';
  # Save the changes back to the file
  # Load xml and verify against XBS ( XML Bare Schema )
  my $xml_text = '<xml><item name=bob/></xml>''
  my $schema_text = '<xml><item* name=[a-z]+></item*></xml>'
  my $ob = new XML::Bare( text => $xml_text, schema => { text => $schema_text } );
  $ob->parse(); # this will error out if schema is invalid


This module is a 'Bare' XML parser. It is implemented in C. The parser itself is a simple state engine that is less than 500 lines of C. The parser builds a C struct tree from input text. That C struct tree is converted to a Perl hash by a Perl function that makes basic calls back to the C to go through the nodes sequentially.

The parser itself will only cease parsing if it encounters tags that are not closed properly. All other inputs will parse, even invalid inputs. To allowing checking for validity, a schema checker is included in the module as well.

The schema format is custom and is meant to be as simple as possible. It is based loosely around the way multiplicity is handled in Perl regular expressions.

Supported XML

To demonstrate what sort of XML is supported, consider the following examples. Each of the PERL statements evaluates to true.

  • Node containing just text

      XML: <xml>blah</xml>
      PERL: $root->{xml}->{value} eq "blah";
  • Subset nodes

      XML: <xml><name>Bob</name></xml>
      PERL: $root->{xml}->{name}->{value} eq "Bob";
  • Attributes unquoted

      XML: <xml><a href=index.htm>Link</a></xml>
      PERL: $root->{xml}->{a}->{href}->{value} eq "index.htm";
  • Attributes quoted

      XML: <xml><a href="index.htm">Link</a></xml>
      PERL: $root->{xml}->{a}->{href}->{value} eq "index.htm";
  • CDATA nodes

      XML: <xml><raw><![CDATA[some raw $~<!bad xml<>]]></raw></xml>
      PERL: $root->{xml}->{raw}->{value} eq "some raw \$~<!bad xml<>";
  • Multiple nodes; form array

      XML: <xml><item>1</item><item>2</item></xml>
      PERL: $root->{xml}->{item}->[0]->{value} eq "1";
  • Forcing array creation

      XML: <xml><multi_item/><item>1</item></xml>
      PERL: $root->{xml}->{item}->[0]->{value} eq "1";
  • One comment supported per node

      XML: <xml><!--test--></xml>
      PERL: $root->{xml}->{comment} eq 'test';

Schema Checking

Schema checking is done by providing the module with an XBS (XML::Bare Schema) to check the XML against. If the XML checks as valid against the schema, parsing will continue as normal. If the XML is invalid, the parse function will die, providing information about the failure.

The following information is provided in the error message:

  • The type of error

  • Where the error occured ( line and char )

  • A short snippet of the XML at the point of failure

XBS ( XML::Bare Schema ) Format

  • Required nodes

      XML: <xml></xml>
      XBS: <xml/>
  • Optional nodes - allow one

      XML: <xml></xml>
      XBS: <xml item?/>
      or XBS: <xml><item?/></xml>
  • Optional nodes - allow 0 or more

      XML: <xml><item/></xml>
      XBS: <xml item*/>
  • Required nodes - allow 1 or more

      XML: <xml><item/><item/></xml>
      XBS: <xml item+/>
  • Nodes - specified minimum and maximum number

      XML: <xml><item/><item/></xml>
      XBS: <xml item{1,2}/>
      or XBS: <xml><item{1,2}/></xml>
      or XBS: <xml><item{1,2}></item{1,2}></xml>
  • Multiple acceptable node formats

      XML: <xml><item type=box volume=20/><item type=line length=10/></xml>
      XBS: <xml><item type=box volume/><item type=line length/></xml>
  • Regular expressions checking for values

      XML: <xml name=Bob dir=up num=10/>
      XBS: <xml name=[A-Za-z]+ dir=up|down num=[0-9]+/>
  • Require multi_ tags

      XML: <xml><multi_item/></xml>
      XBS: <xml item@/>

Parsed Hash Structure

The hash structure returned from XML parsing is created in a specific format. Besides as described above, the structure contains some additional nodes in order to preserve information that will allow that structure to be correctly converted back to XML.

Nodes may contain the following 3 additional subnodes:

  • _i

    The character offset within the original parsed XML of where the node begins. This is used to provide line information for errors when XML fails a schema check.

  • _pos

    This is a number indicating the ordering of nodes. It is used to allow items in a perl hash to be sorted when writing back to xml. Note that items are not sorted after parsing in order to save time if all you are doing is reading and you do not care about the order.

    In future versions of this module an option will be added to allow you to sort your nodes so that you can read them in order. ( note that multiple nodes of the same name are stored in order )

  • _att

    This is a boolean value that exists and is 1 iff the node is an attribute.

Parsing Limitations / Features

  • CDATA parsed correctly, but stripped if unneeded

    Currently the contents of a node that are CDATA are read and put into the value hash, but the hash structure does not have a value indicating the node contains CDATA.

    When converting back to XML, the contents of the value hash are parsed to check for xml incompatible data using a regular expression. If 'CDATA like' stuff is encountered, the node is output as CDATA.

  • Node position stored, but hash remains unsorted

    The ordering of nodes is noted using the '_pos' value, but the hash itself is not ordered after parsing. Currently items will be out of order when looking at them in the hash.

    Note that when converted back to XML, the nodes are then sorted and output in the correct order to XML. Note that nodes of the same name with the same parent will be grouped together; the position of the first item to appear will determine the output position of the group.

  • Comments are parsed but only one is stored per node.

    For each node, there can be a comment within it, and that comment will be saved and output back when dumping to XML.

  • Comments override output of immediate value

    If a node contains only a comment node and a text value, only the comment node will be displayed. This is in line with treating a comment node as a node and only displaying immediate values when a node contains no subnodes.

  • PI sections are parsed, but discarded

  • Unknown <! sections are parsed, but discarded

  • Attributes may use no quotes, single quotes, quotes, or backtics

  • Quoted attributes cannot contain escaped quotes

    No escape character is recognized within quotes. As a result, regular quotes cannot be stored to XML, or the written XML will not be correct, due to all attributes always being written using quotes.

  • Attributes are always written back to XML with quotes

  • Nodes cannot contain subnodes as well as an immediate value

    Actually nodes can in fact contain a value as well, but that value will be discarded if you write back to XML. That value is equal to the first continuous string of text besides a subnode.

      ( the value of node is text )
      ( the value of node is text )
      ( the value of node is "\n  " )
  • Entities are not parsed

    No entity parsing is done. This is intentional. Future versions of the module may include a feature to automatically parse entities, but by default any such feature will be disabled in order to keep from slowing down the parser.

    Also, this is done so that round trip ( read and then write back out ) behavior is consistent.

  • Nodes named value

    Previously iterations of this module had problems with nodes named 'value', due to the fact that node contents are stored under the 'value' key already. The current version should parse such files without any problem, although it may be confusing to see a parsed tree with 'value' pointing to another hash containing 'value' as well.

    In a future version of the module it will be possible to alter the name that values are stored under.

    Note that node values are stored under the key 'content' when the "simple" parsing mode is used, so as to be consistent with XML::Simple.

Module Functions

  • $ob = XML::Bare->new( text => "[some xml]" )

    Create a new XML object, with the given text as the xml source.

  • $object = XML::Bare->new( file => "[filename]" )

    Create a new XML object, with the given filename/path as the xml source

  • $object = XML::Bare->new( text => "[some xml]", file => "[filename]" )

    Create a new XML object, with the given text as the xml input, and the given filename/path as the potential output ( used by save() )

  • $object = XML::Bare->new( file => "data.xml", scheme => { file => "scheme.xbs" } )

    Create a new XML object and check to ensure it is valid xml by way of the XBS scheme.

  • $tree = $object->parse()

    Parse the xml of the object and return a tree reference

  • $tree = $object->simple()

    Alternate to the parse function which generates a tree similar to that generated by XML::Simple. Note that the sets of nodes are turned into arrays always, regardless of whether they have a 'name' attribute, unlike XML::Simple.

    Note that currently the generated tree cannot be used with any of the functions in this module that operate upon trees. The function is provided purely as a quick and dirty way to read simple XML files.

  • $tree = xmlin( $xmlext, keeproot => 1 )

    The xmlin function is a shortcut to creating an XML::Bare object and parsing it using the simple function. It behaves similarly to the XML::Simple function by the same name. The keeproot option is optional and if left out the root node will be discarded, same as the function in XML::Simple.

  • $text = $object->xml( [root] )

    Take the hash tree in [root] and turn it into cleanly indented ( 2 spaces ) XML text.

  • $text = $object->html( [root], [root node name] )

    Take the hash tree in [root] and turn it into nicely colorized and styled html. [root node name] is optional.

  • $object->save()

    The the current tree in the object, cleanly indent it, and save it to the file parameter specified when creating the object.

  • $value = xval $node, $default

    Returns the value of $node or $default if the node does not exist. If default is not passed to the function, then '' is returned as a default value when the node does not exist.

  • ( $name, $age ) = xget( $personnode, qw/name age/ )

    Shortcut function to grab a number of values from a node all at the same time. Note that this function assumes that all of the subnodes exist; it will fail if they do not.

  • $text = XML::Bare::clean( text => "[some xml]" )

    Shortcut to creating an xml object and immediately turning it into clean xml text.

  • $text = XML::Bare::clean( file => "[filename]" )

    Similar to previous.

  • XML::Bare::clean( file => "[filename]", save => 1 )

    Clean up the xml in the file, saving the results back to the file

  • XML::Bare::clean( text => "[some xml]", save => "[filename]" )

    Clean up the xml provided, and save it into the specified file.

  • XML::Bare::clean( file => "[filename1]", save => "[filename2]" )

    Clean up the xml in filename1 and save the results to filename2.

  • $html = XML::Bare::tohtml( text => "[some xml]", root => 'xml' )

    Shortcut to creating an xml object and immediately turning it into html. Root is optional, and specifies the name of the root node for the xml ( which defaults to 'xml' )

  • $object->add_node( [node], [nodeset name], name => value, name2 => value2, ... )

        $object->add_node( $root->{xml}, 'item', name => 'Bob' );
  • $object->add_node_after( [node], [subnode within node to add after], [nodeset name], ... )

  • $object->del_node( [node], [nodeset name], name => value )

        Starting XML:
          $xml->del_node( $root->{xml}, 'a', b=>'1' );
        Ending XML:
  • $object->find_node( [node], [nodeset name], name => value )

        Starting XML:
          $object->find_node( $root->{xml}, 'ob', key => '1' )->{val}->{value} = 'test';
        Ending XML:
  • $object->find_by_perl( [nodeset], "[perl code]" )

    find_by_perl evaluates some perl code for each node in a set of nodes, and returns the nodes where the perl code evaluates as true. In order to easily reference node values, node values can be directly referred to from within the perl code by the name of the node with a dash(-) in front of the name. See the example below.

    Note that this function returns an array reference as opposed to a single node unlike the find_node function.

        Starting XML:
          $object->find_by_perl( $root->{xml}->{ob}, "-key eq '1'" )->[0]->{val}->{value} = 'test';
        Ending XML:
  • XML::Bare::merge( [nodeset1], [nodeset2], [id node name] )

    Merges the nodes from nodeset2 into nodeset1, matching the contents of each node based up the content in the id node.


        my $ob1 = new XML::Bare( text => "
          </xml>" );
        my $ob2 = new XML::Bare( text => "
          </xml>" );
        my $root1 = $ob1->parse();
        my $root2 = $ob2->parse();
        merge( $root1->{'xml'}->{'a'}, $root2->{'xml'}->{'a'}, 'id' );
        print $ob1->xml( $root1 );
  • XML::Bare::del_by_perl( ... )

    Works exactly like find_by_perl, but deletes whatever matches.

  • XML::Bare::forcearray( [noderef] )

    Turns the node reference into an array reference, whether that node is just a single node, or is already an array reference.

  • XML::Bare::new_node( ... )

    Creates a new node...

  • XML::Bare::newhash( ... )

    Creates a new hash with the specified value.

  • XML::Bare::simplify( [noderef] )

    Take a node with children that have immediate values and creates a hashref to reference those values by the name of each child.

  • XML::Bare::hash2xml( [hashref] )

    Take a recursive hash tree ( perhaps generated by the simplify function ) and turn it into a raw XML string. Note that this function does not indent nicely. You will need to feed this string back into the parser and output it again if you want it to look nice. ( or you could use the 'clean' function to do it in one go )

  • XML::Bare->new( text => "[xml]", unsafe => 1 )

    An extra speedy way to parse XML. It is unsafe; may harm pets and children. Don't say you weren't warned. 30% speed boost compared to the normal parsing. You -must- use $ob->simple() in combination with this for it to work properly.

    The speed boost is gained by skipping checks for the end of the string when in the middle of properly formatted XML. The only time the check is done is within "values" ( which includes the space after the final closing </xml> )

    Also, in the unsafe mode, tags, complete with their attributes, must be on one line. Node contents of course, can still have carriage returns...

  • $object->read_more( text => "[xml fragment]" )

    Add more XML text to be handled. Note that this function must be called before calling the parse function.


        my $ob = XML::Bare->new( text => "
            <node>a</node>" );
        $ob->read_more( text => "<node>b</node>" );
        $ob->read_more( text => "</xml>" );
        my $root = $ob->parse();
        print $ob->xml( $root );

    Warning! Reading in additional XML fragments only works properly at proper "division points". Currently the parser will -not- work properly if you split in the middle of a node value, or in the middle of a node name. A future version of the module will be properly updated to handle these cases.

    Currently there is little to no benefit to parsing this way, rather than simple concatenating the two strings together and then reading all the XML in at once.

Functions Used Internally

  • check() checkone() readxbs() free_tree_c()

  • lineinfo() c_parse() c_parse_unsafely() c_parse_more() c_parsefile() free_tree() xml2obj()

  • obj2xml() get_root() obj2html() xml2obj_simple()


Since the creation of this module there has been a fair amount of controvesy surrounding it. A number of authors of other XML parsers have gone so far as to publicly attack this module and claim that it 'does not parse XML', and 'it is not XML compliant'. Some of the same people seem to be angered by the inclusion of a benchmark, claiming that it is an unfair comparison, and that if the proper options and setup are used, that other XML parsers are better.

The module should parse any XML document that conforms to the standardized XML specifications, there is no need for alarm and fear that the module will corrupt your XML documents on reading.

To be blunt about how the parser works, very little has been done to make the parser follow the specification known as 'XML'. The parser is meant to be flexibile and somewhat resilient, and will parse XML like garbage that would cause other parsers to error out.

As far as I am concerned, as the author of the module, the 'XML' in 'XML::Bare' should be thought of to mean 'eXtremely Mad Language', because the module was written from scratch without referring to the specification known as 'XML'.

In regard to the complaints about the unfairness of the included benchmarks, please make your own intelligent decision as to what module you like by trying multiple modules and/or running the performance tests yourself. If you like some other module, use that module. If you like XML::Bare and think it is the fastest thing on the planet, that is cool too.

If you hate XML::Bare and want to go around on the internet trashing it and telling people to use something else, I think perhaps you may want to seek counseling.


In comparison to other available perl xml parsers that create trees, XML::Bare is extremely fast. In order to measure the performance of loading and parsing compared to the alternatives, a templated speed comparison mechanism has been created and included with XML::Bare.

The include file runs when you make the module and creates perl files within the bench directory corresponding to the .tmpl contained there.

Currently there are three types of modules that can be tested against, executable parsers ( exe.tmpl ), tree parsers ( tree.tmpl ), and parsers that do not generated trees ( notree.tmpl ).

A full list of modules currently tested against is as follows:

  EzXML (exe)
  Tiny XML (exe)
  XML::Descent (notree)
  XMLIO (exe)
  XML::LibXML (notree)
  XML::Parser (notree)
  XML::Parser::Expat (notree)
  XML::Simple using XML::Parser
  XML::Simple using XML::SAX::PurePerl
  XML::Simple using XML::LibXML::SAX::Parser
  XML::Simple using XML::Bare::SAX::Parser

To run the comparisons, run the appropriate perl file within the bench directory. (,, or )

The script measures the milliseconds of loading and parsing, and compares the time against the time of XML::Bare. So a 7 means it takes 7 times as long as XML::Bare.

Here is a combined table of the script run against each alternative using the included test.xml:

  -Module-                   load     parse    total
  XML::Bare                  1        1        1
  XML::TreePP                2.3063   33.1776  6.1598
  XML::Parser::EasyTree      4.9405   25.7278  7.4571
  XML::Handler::Trees        7.2303   26.5688  9.6447
  XML::Trivial               5.0636   12.4715  7.3046
  XML::Smart                 6.8138   78.7939  15.8296
  XML::Simple (XML::Parser)  2.3346   50.4772  10.7455
  XML::Simple (PurePerl)     2.361    261.4571 33.6524
  XML::Simple (LibXML)       2.3187   163.7501 23.1816
  XML::Simple (XML::Bare)    2.3252   59.1254  10.9163
  XML::SAX::Simple           8.7792   170.7313 28.3634
  XML::Twig                  27.8266  56.4476  31.3594
  XML::Grove::Builder        7.1267   26.1672  9.4064
  XML::XPath::XMLParser      9.7783   35.5486  13.0002
  XML::LibXML (notree)       11.0038  4.5758   10.6881
  XML::Parser (notree)       4.4698   17.6448  5.8609
  XML::Parser::Expat(notree) 3.7681   50.0382  6.0069
  XML::Descent (notree)      6.0525   37.0265  11.0322
  Tiny XML (exe)                               1.0095
  EzXML (exe)                                  1.1284
  XMLIO (exe)                                  1.0165

Here is a combined table of the script run against each alternative using the included feed2.xml:

  -Module-                   load     parse    total
  XML::Bare                  1        1        1
  XML::Bare (simple)         1        0.7238   ?
  XML::Bare (unsafe simple)  1       ~0.5538   ?
  XML::Fast                  1.516    0.9733   1.4783
  XML::TreePP                0.6393   30.5951  2.6874
  XML::MyXML                 1.8266   14.2571  2.7113 
  XML::Parser::EasyTree      1.5208   22.8283  2.9748 
  XML::Trivial               2.007    25.742   3.615  
  XML::Tiny                  0.1665   61.4918  4.3234  
  XML::XPath::XMLParser      2.5762   33.2567  4.6742  
  XML::Smart                 1.702    59.4907  5.7566
  XML::Simple (XML::Parser)  0.5838   64.7243  5.0006  
  XML::DOM::Lite             4.5207   17.4617  5.4033
  XML::Simple (LibXML)       0.5904   161.7544 11.5731
  XML::Twig                  8.553    56.9034  11.8805 
  XML::Grove::Builder        7.2021   30.7926  12.9334
  XML::Handler::Trees        6.8545   33.1007  13.0575
  XML::LibXML::Simple        14.0204  11.8482  13.8707
  XML::Simple (PurePerl)     0.6176   321.3422 23.0465 
  XML::Simple                2.7168   90.7203  26.7525
  XML::SAX::Simple           8.7386   94.8276  29.2166
  XML::LibXML (notree)       11.0023  5.022    10.5214
  XML::Parser (notree)       4.3748   25.0213  5.9803
  XML::Parser::Expat(notree) 3.6555   51.6426  7.4316
  XML::Descent (notree)      5.9206   155.0289 18.7767
  Tiny XML (exe)                               1.2212
  EzXML (exe)                                  1.3618
  XMLIO (exe)                                  1.0145

These results show that XML::Bare is, at least on the test machine, running all tests within cygwin, faster at loading and parsing than everything being tested against.

The following things are shown as well: - XML::Bare can parse XML and create a hash tree in less time than it takes LibXML just to parse. - XML::Bare can parse XML and create a tree in less time than all three binary parsers take just to parse. - XML::Fast is theoretically faster at parsing than the default 'full' mode of XML::Bare. Despite that, the 'simple' mode of XML::Bare is even faster.

Note that the executable parsers are not perl modules and are timed using dummy programs that just uses the library to load and parse the example files. The executables are not included with this program. Any source modifications used to generate the shown test results can be found in the bench/src directory of the distribution


  Copyright (C) 2008 David Helkowski
  This program is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License as
  published by the Free Software Foundation; either version 2 of the
  License, or (at your option) any later version.  You may also can
  redistribute it and/or modify it under the terms of the Perl
  Artistic License.
  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  GNU General Public License for more details.