git-merge(1)
NAME
git-merge - Join two or more development histories together
SYNOPSIS
git merge [-n] [--stat] [--no-commit] [--squash] [--[no-]edit]
[-s <strategy>] [-X <strategy-option>] [-S[<keyid>]]
[--[no-]allow-unrelated-histories]
[--[no-]rerere-autoupdate] [-m <msg>] [<commit>...]
git merge <msg> HEAD <commit>...
git merge --abort
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>....
The third syntax ("git merge --abort") can only be run after the merge
has resulted in conflicts. 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
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.
--edit, -e, --no-edit
Invoke an editor before committing successful mechanical merge to
further edit the auto-generated merge message, so that the user can
explain and justify the merge. The --no-edit option can be used to
accept the auto-generated message (this is generally discouraged).
The --edit (or -e) option is still useful if you are giving a draft
message with the -m option from the command line and want to edit
it in the editor.
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.
--ff
When the merge resolves as a fast-forward, only update the branch
pointer, without creating a merge commit. This is the default
behavior.
--no-ff
Create a merge commit even when the merge resolves as a
fast-forward. This is the default behaviour when merging an
annotated (and possibly signed) tag.
--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.
--log[=<n>], --no-log
In addition to branch names, populate the log message with one-line
descriptions from at most <n> actual commits that are being merged.
See also git-fmt-merge-msg(1).
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, move the HEAD, or 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.
-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.
--verify-signatures, --no-verify-signatures
Verify that the tip commit of the side branch being merged is
signed with a valid key, i.e. a key that has a valid uid: in the
default trust model, this means the signing key has been signed by
a trusted key. If the tip commit of the side branch is not signed
with a valid key, the merge is aborted.
--summary, --no-summary
Synonyms to --stat and --no-stat; these are deprecated and will be
removed in the future.
-q, --quiet
Operate quietly. Implies --no-progress.
-v, --verbose
Be verbose.
--progress, --no-progress
Turn progress on/off explicitly. If neither is specified, progress
is shown if standard error is connected to a terminal. Note that
not all merge strategies may support progress reporting.
--allow-unrelated-histories
By default, git merge command refuses to merge histories that do
not share a common ancestor. This option can be used to override
this safety when merging histories of two projects that started
their lives independently. As that is a very rare occasion, no
configuration variable to enable this by default exists and will
not be added.
-S[<keyid>], --gpg-sign[=<keyid>]
GPG-sign the resulting merge commit. The keyid argument is optional
and defaults to the committer identity; if specified, it must be
stuck to the option without a space.
-m <msg>
Set the commit message to be used for the merge commit (in case one
is created).
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.
--[no-]rerere-autoupdate
Allow the rerere mechanism to update the index with the result of
auto-conflict resolution if possible.
--abort
Abort the current conflict resolution process, and try to
reconstruct the pre-merge state.
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.
<commit>...
Commits, usually other branch heads, to merge into our branch.
Specifying more than one commit will create a merge with more than
two parents (affectionately called an Octopus merge).
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. (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 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.
<<<<<<< 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 merge --abort 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
mismerges 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. For a binary file, the entire contents are taken from
our side.
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 the opposite of ours.
patience
With this option, merge-recursive spends a little extra time to
avoid mismerges that sometimes occur due to unimportant
matching lines (e.g., braces from distinct functions). Use this
when the branches to be merged have diverged wildly. See also
git-diff(1) --patience.
diff-algorithm=[patience|minimal|histogram|myers]
Tells merge-recursive to use a different diff algorithm, which
can help avoid mismerges that occur due to unimportant matching
lines (such as braces from distinct functions). See also git-
diff(1) --diff-algorithm.
ignore-space-change, ignore-all-space, ignore-space-at-eol
Treats lines with the indicated type of whitespace change as
unchanged for the sake of a three-way merge. Whitespace changes
mixed with other changes to a line are not ignored. See also
git-diff(1) -b, -w, and --ignore-space-at-eol.
* If their version only introduces whitespace changes to a
line, our version is used;
* If our version introduces whitespace changes but their
version includes a substantial change, their version is
used;
* Otherwise, the merge proceeds in the usual way.
renormalize
This runs a virtual check-out and check-in of all three stages
of a file when resolving a three-way merge. This option is
meant to be used when merging branches with different clean
filters or end-of-line normalization rules. See "Merging
branches with differing checkin/checkout attributes" in
gitattributes(5) for details.
no-renormalize
Disables the renormalize option. This overrides the
merge.renormalize configuration variable.
no-renames
Turn off rename detection. See also git-diff(1) --no-renames.
find-renames[=<n>]
Turn on rename detection, optionally setting the similarity
threshold. This is the default. See also git-diff(1)
--find-renames.
rename-threshold=<n>
Deprecated synonym for find-renames=<n>.
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.
With the strategies that use 3-way merge (including the default,
recursive), 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
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.defaultToUpstream
If merge is called without any commit argument, merge the upstream
branches configured for the current branch by using their last
observed values stored in their remote-tracking branches. The
values of the branch.<current branch>.merge that name the branches
at the remote named by branch.<current branch>.remote are
consulted, and then they are mapped via remote.<remote>.fetch to
their corresponding remote-tracking branches, and the tips of these
tracking branches are merged.
merge.ff
By default, Git does not create an extra merge commit when merging
a commit that is a descendant of the current commit. Instead, the
tip of the current branch is fast-forwarded. When set to false,
this variable tells Git to create an extra merge commit in such a
case (equivalent to giving the --no-ff option from the command
line). When set to only, only such fast-forward merges are allowed
(equivalent to giving the --ff-only option from the command line).
merge.branchdesc
In addition to branch names, populate the log message with the
branch description text associated with them. Defaults to false.
merge.log
In addition to branch names, populate the log message with at most
the specified number of one-line descriptions from the actual
commits that are being merged. Defaults to false, and true is a
synonym for 20.
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.renormalize
Tell Git that canonical representation of files in the repository
has changed over time (e.g. earlier commits record text files with
CRLF line endings, but recent ones use LF line endings). In such a
repository, Git can convert the data recorded in commits to a
canonical form before performing a merge to reduce unnecessary
conflicts. For more information, see section "Merging branches with
differing checkin/checkout attributes" in gitattributes(5).
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 tool is used by git-mergetool(1). The list
below shows the valid built-in values. Any other value is treated
as a custom merge tool and requires that a corresponding
mergetool.<tool>.cmd variable is defined.
* araxis
* bc
* bc3
* codecompare
* deltawalker
* diffmerge
* diffuse
* ecmerge
* emerge
* examdiff
* gvimdiff
* gvimdiff2
* gvimdiff3
* kdiff3
* meld
* opendiff
* p4merge
* tkdiff
* tortoisemerge
* vimdiff
* vimdiff2
* vimdiff3
* winmerge
* xxdiff
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)
GIT
Part of the git(1) suite
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