DIFF

Diff is a class of tools that compares two sequences, usually text files, and reports their differences. Its main use is to identify what has changed between versions and to generate a compact representation of those changes, often in the form of a patch.

Most diff tools operate line by line, but some variants can compare words or characters. The standard outputs are diff formats such as unified diff and context diff, which show added and removed lines along with a small context around each change. Patches produced from these diffs can be applied to the original files with a patch utility or integrated into version control workflows.

Algorithms used by diff implementations aim to transform one sequence into the other with as few edits as possible. A widely cited approach is Myers' diff algorithm, which computes a shortest edit script in time proportional to the product of input sizes. Variants and optimizations exist to handle large files or binary data efficiently.

In practice, diff is fundamental in software development for code review, change tracking, and collaboration. It underpins the way version control systems such as Git, Mercurial, and Subversion communicate changes, generate patches, and help merge branches.

Diff originated in early Unix tooling and has become a standard method for expressing and applying changes in text files across computing.