XML::Merge - flexibly merge XML documents


This documentation refers to version 1.4 of XML::Merge, which was released on Sat Jul 23 14:39:59:48 -0500 2016.


  use strict;use   warnings;
  use   utf8;use XML::Merge;

  # create new   XML::Merge object from         MainFile.xml
  my $merge_obj= XML::Merge->new('filename' => 'MainFile.xml');

  # Merge File2Add.xml             into         MainFile.xml
     $merge_obj->merge(          'filename' => 'File2Add.xml');

  # Tidy up the indenting that resulted from the merge

  # Write out changes back           to         MainFile.xml


This module inherits from XML::Tidy which in turn inherits from XML::XPath. This ensures that Merge objects' indenting can be tidied up after any merge operation since such modification usually ruins indentation. Polymorphism allows Merge objects to be utilized as normal XML::XPath objects as well.

The merging behavior is setup to combine separate XML documents according to certain rules and configurable options. If both documents have root nodes which are elements of the same name, the documents are merged directly. Otherwise, one is merged as a child of the other. An optional XPath location can be specified as the place to perform the merge. If no location is specified, the merge is attempted at the first matching element or is appended as the new last child of the other root if no match is found.



This is the standard Merge object constructor. It can take the same parameters as an XML::XPath object constructor to initialize the primary XML document object (the object which subsequent XML documents will be merged into). These parameters can be any one of:

  'filename' => 'SomeFile.xml'
  'xml'      => $variable_which_holds_a_bunch_of_XML_data
  'ioref'    => $file_InputOutput_reference
  'context'  => $existing_node_at_specified_context_to_become_new_obj

Merge's new() can also accept merge-option parameters to override the default merge behavior. These include:

  'conflict_resolution_method' => 'main', # main  file wins
  'conflict_resolution_method' => 'merg', # merge file wins
  # 'last-in_wins' is the same as 'merg'
  'conflict_resolution_method' => 'warn', # croak conflicts
  'conflict_resolution_method' => 'test', # just test, 1 if conflict


The merge() member function can accept the same XML::XPath constructor options as new() but this time they are for the temporary file which will be merged into the main object. Merge-options from new() can also be specified and they will only impact one particular invokation of merge(). The specified document will be merged into the primary XML document object according to the following default merge rules:

1. If both documents share the same root element name, they are merged directly.

2. If they don't share root elements but the temporary merge file's root element is found anywhere within the main file, the merge occurs at the match.

3. If no root element match is found, the merge document becomes the new last child of the main file's root element.

4. Whenever a deeper level is found with an element of the same name in both documents and either it does not contain any distinguishing attributes or it has attributes which are recognized as 'identifier' (id) attributes (by default, for any element, these are attributes named: 'id', 'idx', 'ndx', 'index', 'name', and 'handle'), a corresponding element is searched for to match and merge with.

5. Any remaining (non-id) nodes are merged in document order.

6. When a conflict arises as non-id attributes or other nodes merge, the specified conflict_resolution_method merge-option is applied (which by default has the main file data persist at the expense of the merging file data).

Some of the above rules can be overridden first by the object's merge-options and second by the particular method call's merge-options. Thus, if the default merge-option for conflict resolution is to have the main object win and you use the following constructor:

  my $merge_obj = XML::Merge->new(
    'filename'                   => 'MainFile.xml',
    'conflict_resolution_method' => 'last-in_wins');

... then any $merge_obj->merge() call would override the default merge behavior by letting the document being merged have priority over the main object's document. However, you could supply additional merge-options in the parameter list of your specific merge() call like:

    'filename'                   => 'File2Add.xml',
    'conflict_resolution_method' => 'warn');

... to have the latest option override further.

The 'test' conflict_resolution_method merge-option does not modify the object at all. It solely returns zero (0) if no conflict was encountered from a temporary attempted merge.

It should be used like:

  for(@files) {
    if($merge_obj->merge('cres' => 'test', $_)) {
      croak("Yipes! Conflict with file:$_!\n");
    } else {
      $merge_obj->merge($_); # only do it if there are no conflicts

merge() can also accept another XML::Merge object as a parameter for what to be merged with the main object instead of a filename. An example of this is:


Along with the merge options that can be specified in the object constructor, merge() also accepts the following options to specify where to perform the merge relative to:

  'merge_destination_path' => $main_obj_xpath_location,
  'merge_source_path'      => $merging_obj_xpath_location,


The unmerge() member function is a shorthand for calling both write() and prune() on a certain XPath location which should be written out to a disk file before being removed from the Merge object. Please see XML::Tidy for documentation of the inherited write() and prune() member functions.

This unmerge() process could be the opposite of merge() if no original elements or attributes overlapped and combined but if combining did happen, this would remove original sections of your primary XML document's data from your Merge object so please use this carefully. It is meant to help separate a giant object (probably the result of myriad merge() calls) back into separate useful well-formed XML documents on disk.

unmerge() takes a filename and an xpath_location parameter.



Returns the object which was last merged into the main object.


Assigns the object which was last merged into the main object.


Returns the underlying merge-option conflict_resolution_method.


A new value can be provided as a parameter to be assigned as the XML::Merge object's merge-option.


Returns the underlying id_xpath_list. This is normally just a list of attributes (e.g., '@id', '@idx', '@ndx', '@index', '@name', '@handle') which are unique identifiers for any XML element within merging instance documents. When these attribute names are encountered during a merge(), another element with the same name and attribute value are searched for explicitly in order to align deeper merging and conflict resolution.


A new list can assigned to the XML::Merge object's id_xpath_list.

Please note that this list normally contains XPath attributes so they must be preceded by an at-symbol (@) like: '@example_new_id_attribute'.


Revision history for Perl extension XML::Merge:

- 1.4 G7NMEdxm Sat Jul 23 14:39:59:48 -0500 2016

* inverted conflict resolution 'test' value since true 1 for conflict makes more sense

* renumbered t/*.t

* updated Makefile.PL and Build.PL to hopefully fix issue HTTPS://RT.CPAN.Org/Public/Bug/Display.html?id=29898 (Thanks Kevin.)

* removed DBUG printing

* removed PT from VERSION to fix issue HTTPS://RT.CPAN.Org/Public/Bug/Display.html?id=106873 (Thanks ppisar.)

* updated license to GPLv3

- 1.2.75BAJNl Fri May 11 10:19:23:47 2007

* added default id @s: idx, ndx, and index

- 1.2.565EgGd Sun Jun 5 14:42:16:39 2005

* added use XML::Tidy to make sure exports are available

* removed 02prune.t and moved 03keep.t to 02keep.t ... passing tests is good

- 1.2.4CCJWiB Sun Dec 12 19:32:44:11 2004

* guessing how to fix Darwin test failure @ t/02prune.t first prune() call

- 1.0.4CAL5IS Fri Dec 10 21:05:18:28 2004

* fixed buggy _recmerge

- 1.0.4CAEU0I Fri Dec 10 14:30:00:18 2004

* made accessors for _id_xpath_list

* made _id_xpath_list take XPath locations instead of elem names (old _idea)

* made test _cres (at Marc's request)

* made warn _cres croak

* made Merge inherit from Tidy (which inherits from XPath)

* separated reload(), strip(), tidy(), prune(), and write() into own XML::Tidy module

- 1.0.4C2Nf0R Thu Dec 2 23:41:00:27 2004

* updated license and prep'd for release

- 1.0.4C2BcI2 Thu Dec 2 11:38:18:02 2004

* updated reload(), strip(), and tidy() to verify _xpob exists

- 1.0.4C1JHOl Wed Dec 1 19:17:24:47 2004

* commented out override stuff since it's probably bad form and dumps crap warnings all over tests and causes them to fail... so I guess just uncomment that stuff if you care to preserve PI's and escapes

- 1.0.4C1J7gt Wed Dec 1 19:07:42:55 2004

* made merge() accept merge_source_xpath and merge_destination_xpath params

* made merge() accept other Merge objects

* made reload() not clobber basic escapes (by overriding Text toString())

* made tidy() not kill processing-instructions (by overriding node_test())

* made tidy() not kill comments

- 1.0.4BOHGjm Wed Nov 24 17:16:45:48 2004

* fixed merge() same elems with diff ids bug

- 1.0.4BNBCZL Tue Nov 23 11:12:35:21 2004

* rewrote both merge() and _recmerge() _cres stuff since it was buggy before... so hopefully consistently good now

- 1.0.4BMJCPm Mon Nov 22 19:12:25:48 2004

* fixed merge() for empty elem matching and _cres on text kids

- 1.0.4BMGTLF Mon Nov 22 16:29:21:15 2004

* separated reload() from strip() so that prune() can call it too

- 1.0.4BM0B3x Mon Nov 22 00:11:03:59 2004

* fixed tidy() empty elem bug and implemented prune() and unmerge()

- 1.0.4BJAZpM Fri Nov 19 10:35:51:22 2004

* fixing e() ABSTRACT gen bug

- 1.0.4BJAMR6 Fri Nov 19 10:22:27:06 2004

* fleshed out POD and members

- 1.0.4AIDqmR Mon Oct 18 13:52:48:27 2004

* original version


- add Kevin's multiple _idea option where several element attributes are an ID together, from: <HTTPS://RT.CPAN.Org/Public/Bug/Display.html?id=29897>
- make namespaces and attributes stay in order after merge()
- make text append merge option
- handle comment joins and stamping options
- support modification-time conflict resolution method
- add _ignr ignore list of merge XPath locations to not merge (pre-prune())


From the command shell, please run:

  `perl -MCPAN -e "install XML::Merge"`

or uncompress the package and run the standard:

  `perl Makefile.PL;       make;       make test;       make install`
    or if you don't have  `make` but Module::Build is installed, try:
  `perl    Build.PL; perl Build; perl Build test; perl Build install`


XML::Merge requires:

Carp to allow errors to croak() from calling sub

XML::Tidy to use objects derived from XPath to update XML


Most source code should be Free! Code I have lawful authority over is and shall be! Copyright: (c) 2004-2016, Pip Stuart. Copyleft : This software is licensed under the GNU General Public License (version 3 or later). Please consult HTTP://GNU.Org/licenses/gpl-3.0.txt for important information about your freedom. This is Free Software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. See HTTP://FSF.Org for further information.


Pip Stuart <Pip@CPAN.Org>