git-merge-tree(1)
=================

NAME
----
git-merge-tree - Perform merge without touching index or working tree


SYNOPSIS
--------
[verse]
'git merge-tree' [--write-tree] <branch1> <branch2>
'git merge-tree' [--trivial-merge] <base-tree> <branch1> <branch2> (deprecated)

[[NEWMERGE]]
DESCRIPTION
-----------

This command has a modern `--write-tree` mode and a deprecated
`--trivial-merge` mode.  With the exception of the
<<DEPMERGE,DEPRECATED DESCRIPTION>> section at the end, the rest of
this documentation describes modern `--write-tree` mode.

Performs a merge, but does not make any new commits and does not read
from or write to either the working tree or index.

The performed merge will use the same feature as the "real"
linkgit:git-merge[1], including:

  * three way content merges of individual files
  * rename detection
  * proper directory/file conflict handling
  * recursive ancestor consolidation (i.e. when there is more than one
    merge base, creating a virtual merge base by merging the merge bases)
  * etc.

After the merge completes, a new toplevel tree object is created.  See
`OUTPUT` below for details.

[[OUTPUT]]
OUTPUT
------

For either a successful or conflicted merge, the output from
git-merge-tree is simply one line:

	<OID of toplevel tree>

The printed tree object corresponds to what would be checked out in
the working tree at the end of `git merge`, and thus may have files
with conflict markers in them.

EXIT STATUS
-----------

For a successful, non-conflicted merge, the exit status is 0.  When the
merge has conflicts, the exit status is 1.  If the merge is not able to
complete (or start) due to some kind of error, the exit status is
something other than 0 or 1 (and the output is unspecified).

USAGE NOTES
-----------

This command is intended as low-level plumbing, similar to
linkgit:git-hash-object[1], linkgit:git-mktree[1],
linkgit:git-commit-tree[1], linkgit:git-write-tree[1],
linkgit:git-update-ref[1], and linkgit:git-mktag[1].  Thus, it can be
used as a part of a series of steps such as:

       NEWTREE=$(git merge-tree --write-tree $BRANCH1 $BRANCH2)
       test $? -eq 0 || die "There were conflicts..."
       NEWCOMMIT=$(git commit-tree $NEWTREE -p $BRANCH1 -p $BRANCH2)
       git update-ref $BRANCH1 $NEWCOMMIT

[[DEPMERGE]]
DEPRECATED DESCRIPTION
----------------------

Per the <<NEWMERGE,DESCRIPTION>> and unlike the rest of this
documentation, this section describes the deprecated `--trivial-merge`
mode.

Other than the optional `--trivial-merge`, this mode accepts no
options.

This mode reads three tree-ish, and outputs trivial merge results and
conflicting stages to the standard output in a semi-diff format.
Since this was designed for higher level scripts to consume and merge
the results back into the index, it omits entries that match
<branch1>.  The result of this second form is similar to what
three-way 'git read-tree -m' does, but instead of storing the results
in the index, the command outputs the entries to the standard output.

This form not only has limited applicability (a trivial merge cannot
handle content merges of individual files, rename detection, proper
directory/file conflict handling, etc.), the output format is also
difficult to work with, and it will generally be less performant than
the first form even on successful merges (especially if working in
large repositories).

GIT
---
Part of the linkgit:git[1] suite