GIT-MERGE(1)

NAME
git-merge - Join two or more development histories together

SYNOPSIS

git merge [-n] [--stat] [--no-commit] [--squash]
        [-s <strategy>] [-X <strategy-option>]
        [--[no-]rerere-autoupdate] [-m <msg>] <commit>...
git merge <msg> HEAD <commit>...

DESCRIPTION

Incorporates changes from the named commits (since the time their histories diverged from the current branch) into the current branch. This command is used by git pull to incorporate changes from another repository and can be used by hand to merge changes from one branch into another.

Assume the following history exists and the current branch is "master":

              A---B---C topic
             /
        D---E---F---G master

Then "git merge topic" will replay the changes made on the topic branch since it diverged from master (i.e., E) until its current commit (C) on top of master, and record the result in a new commit along with the names of the two parent commits and a log message from the user describing the changes.

              A---B---C topic
             /         \
        D---E---F---G---H master

The second syntax (<msg> HEAD <commit>...) is supported for historical reasons. Do not use it from the command line or in new scripts. It is the same as git merge -m <msg> <commit>....

Warning: Running git merge with uncommitted changes is discouraged: while possible, it leaves you in a state that is hard to back out of in the case of a conflict.

OPTIONS

--commit, --no-commit
    Perform the merge and commit the result. This option can be used to override --no-commit.

    With --no-commit perform the merge but pretend the merge failed and do not autocommit, to give the user a chance to inspect and further tweak the merge result before committing.

--ff, --no-ff
    Do not generate a merge commit if the merge resolved as a fast-forward, only update the branch pointer. This is the default behavior of git-merge.

    With --no-ff Generate a merge commit even if the merge resolved as a fast-forward.

--log, --no-log
    In addition to branch names, populate the log message with one-line descriptions from the actual commits that are being merged.

    With --no-log do not list one-line descriptions from the actual commits being merged.

--stat, -n, --no-stat
    Show a diffstat at the end of the merge. The diffstat is also controlled by the configuration option merge.stat.

    With -n or --no-stat do not show a diffstat at the end of the merge.

--squash, --no-squash
    Produce the working tree and index state as if a real merge happened (except for the merge information), but do not actually make a commit or move the HEAD, nor record $GIT_DIR/MERGE_HEAD to cause the next git commit command to create a merge commit. This allows you to create a single commit on top of the current branch whose effect is the same as merging another branch (or more in case of an octopus).

    With --no-squash perform the merge and commit the result. This option can be used to override --squash.

--ff-only
    Refuse to merge and exit with a non-zero status unless the current HEAD is already up-to-date or the merge can be resolved as a fast-forward.

-s <strategy>, --strategy=<strategy>
    Use the given merge strategy; can be supplied more than once to specify them in the order they should be tried. If there is no -s option, a built-in list of strategies is used instead (git merge-recursive when merging a single head, git merge-octopus otherwise).

-X <option>, --strategy-option=<option>
    Pass merge strategy specific option through to the merge strategy.

--summary, --no-summary
    Synonyms to --stat and --no-stat; these are deprecated and will be removed in the future.

-q, --quiet
    Operate quietly.

-v, --verbose
    Be verbose.

-m <msg>
    Set the commit message to be used for the merge commit (in case one is created). The git fmt-merge-msg command can be used to give a good default for automated git merge invocations.

--rerere-autoupdate, --no-rerere-autoupdate
    Allow the rerere mechanism to update the index with the result of auto-conflict resolution if possible.

<commit>...
    Commits, usually other branch heads, to merge into our branch. You need at least one <commit>. Specifying more than one <commit> obviously means you are trying an Octopus.

PRE-MERGE CHECKS

Before applying outside changes, you should get your own work in good shape and committed locally, so it will not be clobbered if there are conflicts. See also git-stash(1). git pull and git merge will stop without doing anything when local uncommitted changes overlap with files that git pull/git merge may need to update.

To avoid recording unrelated changes in the merge commit, git pull and git merge will also abort if there are any changes registered in the index relative to the HEAD commit. (One exception is when the changed index entries are in the state that would result from the merge already.)

If all named commits are already ancestors of HEAD, git merge will exit early with the message "Already up-to-date."

FAST-FORWARD MERGE

Often the current branch head is an ancestor of the named commit. This is the most common case especially when invoked from git pull: you are tracking an upstream repository, you have committed no local changes, and now you want to update to a newer upstream revision. In this case, a new commit is not needed to store the combined history; instead, the HEAD (along with the index) is updated to point at the named commit, without creating an extra merge commit.

This behavior can be suppressed with the --no-ff option.

TRUE MERGE

Except in a fast-forward merge (see above), the branches to be merged must be tied together by a merge commit that has both of them as its parents.

A merged version reconciling the changes from all branches to be merged is committed, and your HEAD, index, and working tree are updated to it. It is possible to have modifications in the working tree as long as they do not overlap; the update will preserve them.

When it is not obvious how to reconcile the changes, the following happens:

    1. The HEAD pointer stays the same.

    2. The MERGE_HEAD ref is set to point to the other branch head.

    3. Paths that merged cleanly are updated both in the index file and in your working tree.

    4. For conflicting paths, the index file records up to three versions: stage 1 stores the version from the common ancestor, stage 2 from HEAD, and stage 3 from MERGE_HEAD (you can inspect the stages with git ls-files -u). The working tree files contain the result of the "merge" program; i.e. 3-way merge results with familiar conflict markers <<< === >>>.

    5. No other changes are made. In particular, the local modifications you had before you started merge will stay the same and the index entries for them stay as they were, i.e. matching HEAD.

If you tried a merge which resulted in complex conflicts and want to start over, you can recover with git reset --merge.

HOW CONFLICTS ARE PRESENTED

During a merge, the working tree files are updated to reflect the result of the merge. Among the changes made to the common ancestor's version, non-overlapping ones (that is, you changed an area of the file while the other side left that area intact, or vice versa) are incorporated in the final result verbatim. When both sides made changes to the same area, however, git cannot randomly pick one side over the other, and asks you to resolve it by leaving what both sides did to that area.

By default, git uses the same style as that is used by "merge" program from the RCS suite to present such a conflicted hunk, like this:

    Here are lines that are either unchanged from the common
    ancestor, or cleanly resolved because only one side changed.
    <<<<<<< yours:sample.txt
    Conflict resolution is hard;
    let's go shopping.
    =======
    Git makes conflict resolution easy.
    >>>>>>> theirs:sample.txt
    And here is another line that is cleanly resolved or unmodified.

The area where a pair of conflicting changes happened is marked with markers <<<<<<<, =======, and >>>>>>>. The part before the ======= is typically your side, and the part afterwards is typically their side.

The default format does not show what the original said in the conflicting area. You cannot tell how many lines are deleted and replaced with Barbie's remark on your side. The only thing you can tell is that your side wants to say it is hard and you'd prefer to go shopping, while the other side wants to claim it is easy.

An alternative style can be used by setting the "merge.conflictstyle" configuration variable to "diff3". In "diff3" style, the above conflict may look like this:

    Here are lines that are either unchanged from the common
    ancestor, or cleanly resolved because only one side changed.
    <<<<<<< yours:sample.txt
    Conflict resolution is hard;
    let's go shopping.
    |||||||
    Conflict resolution is hard.
    =======
    Git makes conflict resolution easy.
    >>>>>>> theirs:sample.txt
    And here is another line that is cleanly resolved or unmodified.

In addition to the <<<<<<<, =======, and >>>>>>> markers, it uses another ||||||| marker that is followed by the original text. You can tell that the original just stated a fact, and your side simply gave in to that statement and gave up, while the other side tried to have a more positive attitude. You can sometimes come up with a better resolution by viewing the original.

HOW TO RESOLVE CONFLICTS

After seeing a conflict, you can do two things:

    • Decide not to merge. The only clean-ups you need are to reset the index file to the HEAD commit to reverse 2. and to clean up working tree changes made by 2. and 3.; git-reset --hard can be used for this.

    • Resolve the conflicts. Git will mark the conflicts in the working tree. Edit the files into shape and git add them to the index. Use git commit to seal the deal.

You can work through the conflict with a number of tools:

    • Use a mergetool. git mergetool to launch a graphical mergetool which will work you through the merge.

    • Look at the diffs. git diff will show a three-way diff, highlighting changes from both the HEAD and MERGE_HEAD versions.

    • Look at the diffs from each branch. git log --merge -p <path> will show diffs first for the HEAD version and then the MERGE_HEAD version.

    • Look at the originals. git show :1:filename shows the common ancestor, git show :2:filename shows the HEAD version, and git show :3:filename shows the MERGE_HEAD version.

EXAMPLES

    • Merge branches fixes and enhancements on top of the current branch, making an octopus merge:

        $ git merge fixes enhancements

    • Merge branch obsolete into the current branch, using ours merge strategy:

        $ git merge -s ours obsolete

    • Merge branch maint into the current branch, but do not make a new commit automatically:

        $ git merge --no-commit maint

    This can be used when you want to include further changes to the merge, or want to write your own merge commit message.

    You should refrain from abusing this option to sneak substantial changes into a merge commit. Small fixups like bumping release/version name would be acceptable.

MERGE STRATEGIES

The merge mechanism (git-merge and git-pull commands) allows the backend merge strategies to be chosen with -s option. Some strategies can also take their own options, which can be passed by giving -X<option> arguments to git-merge and/or git-pull.

resolve
    This can only resolve two heads (i.e. the current branch and another branch you pulled from) using a 3-way merge algorithm. It tries to carefully detect criss-cross merge ambiguities and is considered generally safe and fast.

recursive
    This can only resolve two heads using a 3-way merge algorithm. When there is more than one common ancestor that can be used for 3-way merge, it creates a merged tree of the common ancestors and uses that as the reference tree for the 3-way merge. This has been reported to result in fewer merge conflicts without causing mis-merges by tests done on actual merge commits taken from Linux 2.6 kernel development history. Additionally this can detect and handle merges involving renames. This is the default merge strategy when pulling or merging one branch.

    The recursive strategy can take the following options:

    ours
        This option forces conflicting hunks to be auto-resolved cleanly by favoring our version. Changes from the other tree that do not conflict with our side are reflected to the merge result.

        This should not be confused with the ours merge strategy, which does not even look at what the other tree contains at all. It discards everything the other tree did, declaring our history contains all that happened in it.

    theirs
        This is opposite of ours.

    subtree[=path]
        This option is a more advanced form of subtree strategy, where the strategy makes a guess on how two trees must be shifted to match with each other when merging. Instead, the specified path is prefixed (or stripped from the beginning) to make the shape of two trees to match.

octopus
    This resolves cases with more than two heads, but refuses to do a complex merge that needs manual resolution. It is primarily meant to be used for bundling topic branch heads together. This is the default merge strategy when pulling or merging more than one branch.

ours
    This resolves any number of heads, but the resulting tree of the merge is always that of the current branch head, effectively ignoring all changes from all other branches. It is meant to be used to supersede old development history of side branches. Note that this is different from the -Xours option to the recursive merge strategy.

subtree
    This is a modified recursive strategy. When merging trees A and B, if B corresponds to a subtree of A, B is first adjusted to match the tree structure of A, instead of reading the trees at the same level. This adjustment is also done to the common ancestor tree.

CONFIGURATION

merge.conflictstyle
    Specify the style in which conflicted hunks are written out to working tree files upon merge. The default is "merge", which shows a <<<<<<< conflict marker, changes made by one side, a ======= marker, changes made by the other side, and then a >>>>>>> marker. An alternate style, "diff3", adds a ||||||| marker and the original text before the ======= marker.

merge.log
    Whether to include summaries of merged commits in newly created merge commit messages. False by default.

merge.renameLimit
    The number of files to consider when performing rename detection during a merge; if not specified, defaults to the value of diff.renameLimit.

merge.stat
    Whether to print the diffstat between ORIG_HEAD and the merge result at the end of the merge. True by default.

merge.tool
    Controls which merge resolution program is used by git-mergetool(1). Valid built-in values are: "kdiff3", "tkdiff", "meld", "xxdiff", "emerge", "vimdiff", "gvimdiff", "diffuse", "ecmerge", "tortoisemerge", "p4merge", "araxis" and "opendiff". Any other value is treated is custom merge tool and there must be a corresponding mergetool.<tool>.cmd option.

merge.verbosity
    Controls the amount of output shown by the recursive merge strategy. Level 0 outputs nothing except a final error message if conflicts were detected. Level 1 outputs only conflicts, 2 outputs conflicts and file changes. Level 5 and above outputs debugging information. The default is level 2. Can be overridden by the GIT_MERGE_VERBOSITY environment variable.

merge.<driver>.name
    Defines a human-readable name for a custom low-level merge driver. See gitattributes(5) for details.

merge.<driver>.driver
    Defines the command that implements a custom low-level merge driver. See gitattributes(5) for details.

merge.<driver>.recursive
    Names a low-level merge driver to be used when performing an internal merge between common ancestors. See gitattributes(5) for details.

branch.<name>.mergeoptions
    Sets default options for merging into branch <name>. The syntax and supported options are the same as those of git merge, but option values containing whitespace characters are currently not supported.

SEE ALSO

git-fmt-merge-msg(1), git-pull(1), gitattributes(5), git-reset(1), git-diff(1), git-ls-files(1), git-add(1), git-rm(1), git-mergetool(1)

AUTHOR

Written by Junio C Hamano <gitster@pobox.com>

DOCUMENTATION

Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.

GIT

Part of the git(1) suite