Perl module for three-way merge of textual data

 Algorithm::Merge provides three-way merge and diff functions, complementing
 the functionality offered by Algorithm::Diff (libalgorithm-diff-perl). Given
 three sets of items, known as the original, left and right, this module can
 take a three-way difference or merge them. Taking a difference provides an
 array reference that is very similar to the behaviour of Algorithm::Diff. One
 can also implement custom conflict resolution using the CONFLICT callback.