NAME

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

SYNOPSIS

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

DESCRIPTION

       This command has a modern --write-tree mode and a deprecated --trivial-merge mode. With
       the exception of the 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" 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.

OPTIONS

       -z
           Do not quote filenames in the <Conflicted file info> section, and end each filename
           with a NUL character rather than newline. Also begin the messages section with a NUL
           character instead of a newline. See the section called “OUTPUT” below for more
           information.

       --name-only
           In the Conflicted file info section, instead of writing a list of (mode, oid, stage,
           path) tuples to output for conflicted files, just provide a list of filenames with
           conflicts (and do not list filenames multiple times if they have multiple conflicting
           stages).

       --[no-]messages
           Write any informational messages such as "Auto-merging <path>" or CONFLICT notices to
           the end of stdout. If unspecified, the default is to include these messages if there
           are merge conflicts, and to omit them otherwise.

       --allow-unrelated-histories
           merge-tree will by default error out if the two branches specified share no common
           history. This flag can be given to override that check and make the merge proceed
           anyway.

OUTPUT

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

           <OID of toplevel tree>

       Whereas for a conflicted merge, the output is by default of the form:

           <OID of toplevel tree>
           <Conflicted file info>
           <Informational messages>

       These are discussed individually below.

       However, there is an exception. If --stdin is passed, then there is an extra section at
       the beginning, a NUL character at the end, and then all the sections repeat for each line
       of input. Thus, if the first merge is conflicted and the second is clean, the output would
       be of the form:

           <Merge status>
           <OID of toplevel tree>
           <Conflicted file info>
           <Informational messages>
           NUL
           <Merge status>
           <OID of toplevel tree>
           NUL

   Merge status
       This is an integer status followed by a NUL character. The integer status is:

           0: merge had conflicts
           1: merge was clean
           &lt;0: something prevented the merge from running (e.g. access to repository
               objects denied by filesystem)

   OID of toplevel tree
       This is a tree object that represents what would be checked out in the working tree at the
       end of git merge. If there were conflicts, then files within this tree may have embedded
       conflict markers. This section is always followed by a newline (or NUL if -z is passed).

   Conflicted file info
       This is a sequence of lines with the format

           <mode> <object> <stage> <filename>

       The filename will be quoted as explained for the configuration variable core.quotePath
       (see git-config(1)). However, if the --name-only option is passed, the mode, object, and
       stage will be omitted. If -z is passed, the "lines" are terminated by a NUL character
       instead of a newline character.

   Informational messages
       This section provides informational messages, typically about conflicts. The format of the
       section varies significantly depending on whether -z is passed.

       If -z is passed:

       The output format is zero or more conflict informational records, each of the form:

           <list-of-paths><conflict-type>NUL<conflict-message>NUL

       where <list-of-paths> is of the form

           <number-of-paths>NUL<path1>NUL<path2>NUL...<pathN>NUL

       and includes paths (or branch names) affected by the conflict or informational message in
       <conflict-message>. Also, <conflict-type> is a stable string explaining the type of
       conflict, such as

       •   "Auto-merging"

       •   "CONFLICT (rename/delete)"

       •   "CONFLICT (submodule lacks merge base)"

       •   "CONFLICT (binary)"

       and <conflict-message> is a more detailed message about the conflict which often (but not
       always) embeds the <stable-short-type-description> within it. These strings may change in
       future Git versions. Some examples:

       •   "Auto-merging <file>"

       •   "CONFLICT (rename/delete): <oldfile> renamed...but deleted in..."

       •   "Failed to merge submodule <submodule> (no merge base)"

       •   "Warning: cannot merge binary files: <filename>"

       If -z is NOT passed:

       This section starts with a blank line to separate it from the previous sections, and then
       only contains the <conflict-message> information from the previous section (separated by
       newlines). These are non-stable strings that should not be parsed by scripts, and are just
       meant for human consumption. Also, note that while <conflict-message> strings usually do
       not contain embedded newlines, they sometimes do. (However, the free-form messages will
       never have an embedded NUL character). So, the entire block of information is meant for
       human readers as an agglomeration of all conflict messages.

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). When --stdin is passed, the return status is 0 for both successful and
       conflicted merges, and something other than 0 or 1 if it cannot complete all the requested
       merges.

USAGE NOTES

       This command is intended as low-level plumbing, similar to git-hash-object(1), git-
       mktree(1), git-commit-tree(1), git-write-tree(1), git-update-ref(1), and 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

       Note that when the exit status is non-zero, NEWTREE in this sequence will contain a lot
       more output than just a tree.

       For conflicts, the output includes the same information that you’d get with git-merge(1):

       •   what would be written to the working tree (the OID of toplevel tree)

       •   the higher order stages that would be written to the index (the Conflicted file info)

       •   any messages that would have been printed to stdout (the Informational messages)

MISTAKES TO AVOID

       Do NOT look through the resulting toplevel tree to try to find which files conflict; parse
       the Conflicted file info section instead. Not only would parsing an entire tree be
       horrendously slow in large repositories, there are numerous types of conflicts not
       representable by conflict markers (modify/delete, mode conflict, binary file changed on
       both sides, file/directory conflicts, various rename conflict permutations, etc.)

       Do NOT interpret an empty Conflicted file info list as a clean merge; check the exit
       status. A merge can have conflicts without having individual files conflict (there are a
       few types of directory rename conflicts that fall into this category, and others might
       also be added in the future).

       Do NOT attempt to guess or make the user guess the conflict types from the Conflicted file
       info list. The information there is insufficient to do so. For example:
       Rename/rename(1to2) conflicts (both sides renamed the same file differently) will result
       in three different file having higher order stages (but each only has one higher order
       stage), with no way (short of the Informational messages section) to determine which three
       files are related. File/directory conflicts also result in a file with exactly one higher
       order stage. Possibly-involved-in-directory-rename conflicts (when
       "merge.directoryRenames" is unset or set to "conflicts") also result in a file with
       exactly one higher order stage. In all cases, the Informational messages section has the
       necessary info, though it is not designed to be machine parseable.

       Do NOT assume that each paths from Conflicted file info, and the logical conflicts in the
       Informational messages have a one-to-one mapping, nor that there is a one-to-many mapping,
       nor a many-to-one mapping. Many-to-many mappings exist, meaning that each path can have
       many logical conflict types in a single merge, and each logical conflict type can affect
       many paths.

       Do NOT assume all filenames listed in the Informational messages section had conflicts.
       Messages can be included for files that have no conflicts, such as "Auto-merging <file>".

       AVOID taking the OIDS from the Conflicted file info and re-merging them to present the
       conflicts to the user. This will lose information. Instead, look up the version of the
       file found within the OID of toplevel tree and show that instead. In particular, the
       latter will have conflict markers annotated with the original branch/commit being merged
       and, if renames were involved, the original filename. While you could include the original
       branch/commit in the conflict marker annotations when re-merging, the original filename is
       not available from the Conflicted file info and thus you would be losing information that
       might help the user resolve the conflict.

DEPRECATED DESCRIPTION

       Per the 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 git(1) suite