Document git-merge-file

Most of this is derived from the documentation of RCS merge.

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-merge-file.txt

@@ -0,0 +1,92 @@
+git-merge-file(1)
+============
+
+NAME
+----
+git-merge-file - threeway file merge
+
+
+SYNOPSIS
+--------
+[verse]
+'git-merge-file' [-L <current-name> [-L <base-name> [-L <other-name>]]]
+	[-p|--stdout] [-q|--quiet] <current-file> <base-file> <other-file>
+
+
+DESCRIPTION
+-----------
+git-file-merge incorporates all changes that lead from the `<base-file>`
+to `<other-file>` into `<current-file>`. The result ordinarily goes into
+`<current-file>`. git-merge-file is useful for combining separate changes
+to an original. Suppose `<base-file>` is the original, and both
+`<current-file>` and `<other-file>` are modifications of `<base-file>`.
+Then git-merge-file combines both changes.
+
+A conflict occurs if both `<current-file>` and `<other-file>` have changes
+in a common segment of lines. If a conflict is found, git-merge-file
+normally outputs a warning and brackets the conflict with <<<<<<< and
+>>>>>>> lines. A typical conflict will look like this:
+
+	<<<<<<< A
+	lines in file A
+	=======
+	lines in file B
+	>>>>>>> B
+
+If there are conflicts, the user should edit the result and delete one of
+the alternatives.
+
+The exit value of this program is negative on error, and the number of
+conflicts otherwise. If the merge was clean, the exit value is 0.
+
+git-merge-file is designed to be a minimal clone of RCS merge, that is, it
+implements all of RCS merge's functionality which is needed by
+gitlink:git[1].
+
+
+OPTIONS
+-------
+
+-L <label>::
+	This option may be given up to three times, and
+	specifies labels to be used in place of the
+	corresponding file names in conflict reports. That is,
+	`git-merge-file -L x -L y -L z a b c` generates output that
+	looks like it came from files x, y and z instead of
+	from files a, b and c.
+
+-p::
+	Send results to standard output instead of overwriting
+	`<current-file>`.
+
+-q::
+	Quiet;  do  not  warn about conflicts.
+
+
+EXAMPLES
+--------
+
+git merge-file README.my README README.upstream::
+
+	combines the changes of README.my and README.upstream since README,
+	tries to merge them and writes the result into README.my.
+
+git merge-file -L a -L b -L c tmp/a123 tmp/b234 tmp/c345::
+
+	merges tmp/a123 and tmp/c345 with the base tmp/b234, but uses labels
+	`a` and `c` instead of `tmp/a123` and `tmp/c345`.
+
+
+Author
+------
+Written by Johannes Schindelin <johannes.schindelin@gmx.de>
+
+
+Documentation
+--------------
+Documentation by Johannes Schindelin and the git-list <git@vger.kernel.org>,
+with parts copied from the original documentation of RCS merge.
+
+GIT
+---
+Part of the gitlink:git[7] suite

Documentation/git.txt

@@ -351,6 +351,9 @@ gitlink:git-init-db[1]::
 	Creates an empty git object database, or reinitialize an
 	existing one.
 
+gitlink:git-merge-file[1]::
+	Runs a threeway merge.
+
 gitlink:git-merge-index[1]::
 	Runs a merge for files needing merging.