unwrapdiff

unwrapdiff [OPTION]... [FILE]

--help
    Displays a help message and exits.

--version
    Displays version information and exits.

unwrapdiff is a utility often distributed as part of the patch package. Its primary function is to transform a "context diff" that uses indentation to denote context lines (typically generated by tools like wrapdiff or certain diff -c outputs) into a more conventional format, resembling a "unified diff".

Context diffs, as the name suggests, include several lines of unchanged context around modifications. When these context lines are prefixed with spaces (e.g., two spaces) to visually indent them, unwrapdiff strips these leading spaces. This effectively flattens the indentation and presents the diff in a format that is often more compact and easier for other tools (like patch) or human readers to parse, especially if they expect a unified-like format.

It's important to note that unwrapdiff does not generate diffs between files; rather, it transforms the format of an existing diff output. It is most commonly used in conjunction with wrapdiff (to reverse its action) or to preprocess diffs that were generated with excessive context indentation.

Input Format Dependency: unwrapdiff expects a specific input format, typically a context diff where context lines are prefixed with leading spaces. If the input does not conform to this structure, the output will likely be garbled or incorrect.

No Diff Generation: This command is a transformation utility; it cannot generate a diff from two files. It only processes an already existing diff output.

Plain Text Only: Like most diff utilities, unwrapdiff is designed to work with plain text files and does not handle binary file differences.

The command primarily expects input from a context diff where context lines (unchanged lines providing surrounding reference) are prefixed by leading spaces (e.g., two spaces). Changed lines typically start with '+' or '-'. This distinct indentation allows unwrapdiff to identify and remove the excess spaces.

Upon successful processing, unwrapdiff outputs a transformed diff. The context lines will no longer have the leading spaces, making the output appear more like a standard unified diff format (where context lines are not prefixed, or simply start with a space for a context line in a unified diff, but the point here is removing the extra indentation that wrapdiff specifically adds). This makes the output more amenable to tools that expect a less indented or unified-like diff structure.

unwrapdiff is part of the GNU patch utilities, which have a long history in the Unix and Linux ecosystems. It was developed to complement wrapdiff, providing a mechanism to reverse the indentation that wrapdiff applies to context lines in diff outputs. Its development is tied to the evolution of source code management and patch distribution methodologies, where transforming diff formats for various purposes became necessary.

patch(1), diff(1), wrapdiff(1), sdiff(1), diff3(1)