Unified diff

Unified diff (or diff unified format, unified context diff, unidiff) is a diff format commonly used for patch files.

Identification
Unlike other diff formats, Unified diff has lines that begin with "@@".

Specifications

 * Unified Diff Format - Ad-hoc specification by Guido van Rossum
 * GNU Diffutilis manual: Detailed Description of Unified Format

Software

 * GNU Diffutils:  (with   option),

Sample files

 * Example from the GNU Diffutils manual
 * http://www.apache.org/dist/httpd/patches/ ...

Links

 * Wikipedia:Diff utility has a section on Unified diff