git-merge(1)

NAME#

git-merge - Join two or more development histories together

SYNOPSIS#

git merge\n [-n] [--stat] [--no-commit] [--squash] [--[no-]edit]
\n
        [--no-verify] [-s <strategy>] [-X <strategy-option>] [-S[<keyid>]]
\n
        [--[no-]allow-unrelated-histories]
\n
        [--[no-]rerere-autoupdate] [-m <msg>] [-F <file>]
\n
        [--into-name <branch>] [<commit>...]
\ngit merge\n (--continue | --abort | --quit)

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:

\n
          A---B---C topic
\n
         /
\n
    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. Before the operation, ORIG_HEAD is set to the tip of the current branch (C).

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

A merge stops if there’s a conflict that cannot be resolved automatically or if --no-commit was provided when initiating the merge. At that point you can run git merge --abort or git merge --continue.

git merge --abort will abort the merge process and try to reconstruct the pre-merge state. However, if there were uncommitted changes when the merge started (and especially if those changes were further modified after the merge was started), git merge --abort will in some cases be unable to reconstruct the original (pre-merge) changes. Therefore:

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

OPTIONS#

--commit, --no-commit

With --no-commit perform the merge and stop just before creating a merge commit, to give the user a chance to inspect and further tweak the merge result before committing.

Note that fast-forward updates do not create a merge commit and therefore there is no way to stop those merges with --no-commit. Thus, if you want to ensure your branch is not changed or updated by the merge command, use --no-ff with --no-commit.

--edit, -e, --no-edit

Older scripts may depend on the historical behaviour of not allowing the user to edit the merge log message. They will see an editor opened when they run git merge. To make it easier to adjust such scripts to the updated behaviour, the environment variable GIT_MERGE_AUTOEDIT can be set to no at the beginning of them.

--cleanup=<mode>

--ff, --no-ff, --ff-only

With --ff, when possible resolve the merge as a fast-forward (only update the branch pointer to match the merged branch; do not create a merge commit). When not possible (when the merged-in history is not a descendant of the current history), create a merge commit.

With --no-ff, create a merge commit in all cases, even when the merge could instead be resolved as a fast-forward.

With --ff-only, resolve the merge as a fast-forward when possible. When not possible, refuse to merge and exit with a non-zero status.

-S[<keyid>], --gpg-sign[=<keyid>], --no-gpg-sign

--log[=<n>], --no-log

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

--signoff, --no-signoff

The --no-signoff option can be used to countermand an earlier --signoff option on the command line.

--stat, -n, --no-stat

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

--squash, --no-squash

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

With --squash, --commit is not allowed, and will fail.

--[no-]verify

-s <strategy>, --strategy=<strategy>

-X <option>, --strategy-option=<option>

--verify-signatures, --no-verify-signatures

--summary, --no-summary

-q, --quiet

-v, --verbose

--progress, --no-progress

--autostash, --no-autostash

--allow-unrelated-histories

-m <msg>

If --log is specified, a shortlog of the commits being merged will be appended to the specified message.

The git fmt-merge-msg command can be used to give a good default for automated git merge invocations. The automated message can include the branch description.

--into-name <branch>

-F <file>, --file=<file>

If --log is specified, a shortlog of the commits being merged will be appended to the specified message.

--rerere-autoupdate, --no-rerere-autoupdate

--overwrite-ignore, --no-overwrite-ignore

--abort

If there were uncommitted worktree changes present when the merge started, git merge --abort will in some cases be unable to reconstruct these changes. It is therefore recommended to always commit or stash your changes before running git merge.

git merge --abort is equivalent to git reset --merge when MERGE_HEAD is present unless MERGE_AUTOSTASH is also present in which case git merge --abort applies the stash entry to the worktree whereas git reset --merge will save the stashed changes in the stash list.

--quit

--continue

<commit>...

If no commit is given from the command line, merge the remote-tracking branches that the current branch is configured to use as its upstream. See also the configuration section of this manual page.

When FETCH_HEAD (and no other commit) is specified, the branches recorded in the .git/FETCH_HEAD file by the previous invocation of git fetch for merging are merged to the current branch.

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. (Special narrow exceptions to this rule may exist depending on which merge strategy is in use, but generally, the index must match HEAD.)

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:

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

MERGING TAG#

When merging an annotated (and possibly signed) tag, Git always creates a merge commit even if a fast-forward merge is possible, and the commit message template is prepared with the tag message. Additionally, if the tag is signed, the signature check is reported as a comment in the message template. See also git-tag(1).

When you want to just integrate with the work leading to the commit that happens to be tagged, e.g. synchronizing with an upstream release point, you may not want to make an unnecessary merge commit.

In such a case, you can "unwrap" the tag yourself before feeding it to git merge, or pass --ff-only when you do not have any work on your own. e.g.

git fetch origin
git merge v1.2.3^0
git merge --ff-only v1.2.3

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 the one used by the "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,
or cleanly resolved because both sides changed the same way.
<<<<<<< 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 either "diff3" or "zdiff3". 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
or cleanly resolved because both sides changed the same way.
Conflict resolution is hard;
let's go shopping.
||||||| base:sample.txt
or cleanly resolved because both sides changed identically.
Conflict resolution is hard.
=======
or cleanly resolved because both sides changed the same way.
Git makes conflict resolution easy.
>>>>>>> theirs:sample.txt
And here is another line that is cleanly resolved or unmodified.

while in "zdiff3" style, it may look like this:

Here are lines that are either unchanged from the common
ancestor, or cleanly resolved because only one side changed,
or cleanly resolved because both sides changed the same way.
<<<<<<< yours:sample.txt
Conflict resolution is hard;
let's go shopping.
||||||| base:sample.txt
or cleanly resolved because both sides changed identically.
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:

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

EXAMPLES#

$ git merge fixes enhancements

$ git merge -s ours obsolete

$ 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.

ort

The ort strategy can take the following options:

ours

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

ignore-space-change, ignore-all-space, ignore-space-at-eol, ignore-cr-at-eol

renormalize

no-renormalize

find-renames[=<n>]

rename-threshold=<n>

subtree[=<path>]

recursive

The recursive strategy takes the same options as ort. However, there are three additional options that ort ignores (not documented above) that are potentially useful with the recursive strategy:

patience

diff-algorithm=[patience|minimal|histogram|myers]

no-renames

resolve

octopus

ours

subtree

With the strategies that use 3-way merge (including the default, ort), if a change is made on both branches, but later reverted on one of the branches, that change will be present in the merged result; some people find this behavior confusing. It occurs because only the heads and the merge base are considered when performing a merge, not the individual commits. The merge algorithm therefore considers the reverted change as no change at all, and substitutes the changed version instead.

CONFIGURATION#

branch.<name>.mergeOptions

Everything above this line in this section isn’t included from the git-config(1) documentation. The content that follows is the same as what’s found there:

merge.conflictStyle

merge.defaultToUpstream

merge.ff

merge.verifySignatures

merge.branchdesc

merge.log

merge.suppressDest

An element with an empty value can be used to clear the list of globs accumulated from previous configuration entries. When there is no merge.suppressDest variable defined, the default value of master is used for backward compatibility.

merge.renameLimit

merge.renames

merge.directoryRenames

merge.renormalize

merge.stat

merge.autoStash

merge.tool

merge.guitool

araxis

bc

bc3

bc4

codecompare

deltawalker

diffmerge

diffuse

ecmerge

emerge

examdiff

guiffy

gvimdiff

gvimdiff1

gvimdiff2

gvimdiff3

kdiff3

meld

nvimdiff

nvimdiff1

nvimdiff2

nvimdiff3

opendiff

p4merge

smerge

tkdiff

tortoisemerge

vimdiff

vimdiff1

vimdiff2

vimdiff3

vscode

winmerge

xxdiff

merge.verbosity

merge.<driver>.name

merge.<driver>.driver

merge.<driver>.recursive

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)

GIT#

Part of the git(1) suite