combinediff

combinediff [OPTIONS] DIFF1 DIFF2 [ORIGINAL_FILE1] [ORIGINAL_FILE2]

DIFF1
    The path to the first diff file (patch) to be combined.

DIFF2
    The path to the second diff file (patch) to be combined.

ORIGINAL_FILE1
    (Optional) The path to the original file from which DIFF1 was generated. Used to determine the exact base for comparison.

ORIGINAL_FILE2
    (Optional) The path to the original file from which DIFF2 was generated. Used in conjunction with ORIGINAL_FILE1 to produce a diff from FILE1 (modified by DIFF1) to FILE2 (modified by DIFF2).

-p NUM
    Instructs the underlying patch command to strip NUM leading path components from file names in the diffs.

-q
    Operate in quiet mode, suppressing non-essential output.

-v
    Enable verbose output, providing more details about the process.

-d
    Enable debug mode, showing internal commands and temporary files.

-s
    Suppress errors from the underlying diff command.

-i
    Ignore changes in amount of white space.

-w
    Ignore all white space when comparing lines.

-b
    Ignore changes in the amount of white space (but not actual white space characters).

-B
    Ignore changes that consist solely of blank lines.

-I REGEXP
    Ignore changes whose lines match the specified regular expression.

-c CONTEXT
    Set the number of context lines to CONTEXT for the output diff (default is usually 3).

-u
    Force output to be in unified diff format (this is often the default).

-N
    Treat absent files as empty when comparing.

-o FILE
    Direct the output of the combined diff to FILE instead of standard output.

--diff-options ...
    Pass additional options directly to the underlying diff command used by combinediff.

--strip-trailing-cr
    Strip trailing carriage returns (CR) from input lines, useful when dealing with Windows/Unix line ending differences.

combinediff is a command-line utility designed to merge two patch files (diffs) that originated from the same base or original source file. It processes these two input diffs and produces a single, consolidated patch file as output.

This tool is particularly valuable in software development and version control contexts where changes from different branches or sets of modifications need to be integrated. Rather than applying two separate patches sequentially, combinediff enables the creation of a single patch that encapsulates all combined changes, streamlining the patching process.

It functions by analyzing the modifications described in both input diffs relative to their implied common ancestor. It then intelligently merges these changes, attempting to resolve overlaps and potential conflicts where possible. The resulting output is typically in the unified diff format, showing the aggregate transformation from the base file to a state reflecting both sets of modifications, or from one patched version to another, depending on the command's invocation.

combinediff works most reliably when both input diffs (DIFF1 and DIFF2) are generated against a genuinely common original file. If the base files are significantly divergent or the diffs are not well-formed, the results may be unpredictable or incorrect. While it attempts to merge changes, it is not a full-fledged merge tool like git merge and may not handle complex overlapping conflicts gracefully, potentially producing a patch that requires manual intervention to apply cleanly.

At its core, combinediff conceptually performs a multi-step process: it reconstructs the original file(s) from the diffs if not provided, applies one diff to the original to get an intermediate state, and then generates a new diff between this intermediate state and the state resulting from applying the other diff. Alternatively, if two original files are provided, it generates a diff between the state of ORIGINAL_FILE1 after DIFF1 and the state of ORIGINAL_FILE2 after DIFF2.

• Creating Delta Patches: Generating a patch that transforms a file from a state where DIFF1 was applied to a state where DIFF2 was applied, assuming both originated from a common ancestor.
• Consolidating Changes: Merging two distinct sets of modifications (e.g., two bug fixes, or a bug fix and a feature) that both apply to the same base version of a file into a single, unified patch file. This simplifies distribution and application of changes.

combinediff is typically distributed as part of the `patch` utilities, a suite of tools fundamental to Unix-like systems for managing and applying code changes. The original `patch` program was written by Larry Wall in 1985. combinediff serves as a higher-level script that leverages the core `diff` and `patch` functionalities to solve a specific problem of combining multiple sets of changes. Its development reflects a Unix philosophy of creating simple, composable tools to achieve complex tasks, preceding the widespread adoption of modern distributed version control systems which often incorporate similar merging capabilities directly.

diff(1), patch(1), merge(1), git-diff(1)