merge

merge [-p] [-A] [-E] [-e] [-x] [-i] [-f] [-a] [-q] [-n] [-T] file1 file2 file3

-p
    Display the result of the merge to standard output instead of modifying the file.

-A
    When encountering conflicts, output an augmented format containing the original common ancestor text in addition to the conflicting revisions.

-E
    Generate an output with conflict markers that include the original revision numbers.

-e
    Use an alternate editor to merge the files interactively.

-x
    Display extra context in the conflict markers.

-i
    Ignore case differences when comparing lines.

-f
    Force the merge even if the working file has local modifications. This can lead to data loss if not handled carefully.

-a
    Treat all differences as additions.

-q
    Run in quiet mode, suppressing most output messages.

-n
    Do not save the merged result to the file. Useful for previewing the merge.

-T
    Do not use temporary files during the merge process.

file1
    The first file to merge (typically the common ancestor).

file2
    The second file to merge.

file3
    The third file to merge (typically the working file). The result is written into this file.

The `merge` command combines changes from two different revisions of a file, typically managed by a version control system like RCS or CVS, into a working file. It's a vital tool for resolving conflicts that arise when multiple users modify the same file concurrently. `merge` analyzes the common ancestor revision and the two diverging revisions to identify the changes made in each. It then attempts to automatically integrate these changes into the working file. If conflicts are detected (i.e., changes made to the same lines in both revisions), `merge` inserts conflict markers into the file, delineating the conflicting sections. Users must manually resolve these conflicts by editing the file and removing the markers before committing the merged file back to the repository. The command helps to maintain code integrity when many developers contribute to the same project.

Typically the file being merged is the working file. One or more of the other files is a version from the RCS or CVS repository. The result is a modified working file with conflict markers if needed.

The `merge` command heavily relies on the accuracy of the common ancestor file. Incorrect or missing ancestor information can lead to inaccurate merges and potentially corrupt the working file. Always ensure that the ancestor file is the true common ancestor of the two revisions being merged. Backup of important files before usage of merge command is highly recommended.

When `merge` encounters conflicting changes, it inserts special markers into the file. These markers typically look like `<<<<<<<`, `=======`, and `>>>>>>>`. The text between `<<<<<<<` and `=======` represents the changes from one revision, and the text between `=======` and `>>>>>>>` represents the changes from the other revision. The user must manually edit the file, resolve the conflicting changes, and remove these markers.

When used with CVS, you would typically invoke `merge` by specifying the `-r` option to identify the revisions you want to merge. `cvs update -j` can be a more effective solution.

The `merge` command has roots in early version control systems like RCS and CVS. It was created to deal with the problem of simultaneous changes made by multiple developers. The specific implementation and features can vary between different version control systems, but the core functionality of merging file revisions remains consistent.

rcs(1), cvs(1), diff(1), patch(1)