Manual:$wgExternalDiffEngine

Details
Name of the external diff engine to use, or false to use the internal engine.

The possible values are:


 * -  if available, PHP implementation else.
 * - Wikimedia's fast difference engine implemented as a PHP/HHVM module.
 * - treated as false for backwards compatibility.


 * any other string is treated as a path to external diff executable, which is passed two file-path arguments.

The external engine should return HTML for a table row containing four columns (two 'marker/content' pairs). These can be collapsed into one for diff formats that don't require columns, e.g.

This setting replaces.

Example
To display diffs in the format of the common GNU  program, it is necessary to wrap that executable in a small script such as the following. This is needed both to get the required HTML wrapper, and also because  returns non-zero when inputs don't match (which they generally don't for wiki changes).


 * externaldiff.sh
 * LocalSettings.php