GIT-MERGE(1)GIT-MERGE(1)NAMEgit-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 his-
tories diverged from the current branch) into the current branch. This
command is used by git pull to incorporate changes from another reposi-
tory 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":
.ft C
A---B---C topic
/
D---E---F---G master
.ft
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.
.ft C
A---B---C topic
/ \
D---E---F---G---H master
.ft
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:
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GIT-MERGE(1)GIT-MERGE(1)
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 hap-
pened (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.
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GIT-MERGE(1)GIT-MERGE(1)--ff-only
Refuse to merge and exit with a non-zero status unless the cur-
rent 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 strat-
egy.
--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).
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.
--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 <com-
mit> obviously means you are trying an Octopus.
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GIT-MERGE(1)GIT-MERGE(1)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 hap-
pens:
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.
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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 ances-
tor’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:
.ft C
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.
.ft
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
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GIT-MERGE(1)GIT-MERGE(1)
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 pre-
fer 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:
.ft C
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.
.ft
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 resolu-
tion by viewing the original.
HOW TO RESOLVE CONFLICTS
After seeing a conflict, you can do two things:
o 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.
o 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:
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GIT-MERGE(1)GIT-MERGE(1)
o Use a mergetool. git mergetool to launch a graphical mergetool which
will work you through the merge.
o Look at the diffs. git diff will show a three-way diff, highlighting
changes from both the HEAD and MERGE_HEAD versions.
o 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 ver-
sion.
o Look at the originals. git show :1:filename shows the common ances-
tor, git show :2:filename shows the HEAD version, and git show
:3:filename shows the MERGE_HEAD version.
EXAMPLES
o Merge branches fixes and enhancements on top of the current branch,
making an octopus merge:
.ft C
$ git merge fixes enhancements
.ft
o Merge branch obsolete into the current branch, using ours merge
strategy:
.ft C
$ git merge -s ours obsolete
.ft
o Merge branch maint into the current branch, but do not make a new
commit automatically:
.ft C
$ git merge --no-commit maint
.ft
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
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changes into a merge commit. Small fixups like bumping release/ver-
sion name would be acceptable.
MERGE STRATEGIES
The merge mechanism (git-merge and git-pull commands) allows the back-
end 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.
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
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GIT-MERGE(1)GIT-MERGE(1)
checkin/checkout attributes" in gitattributes(5) for
details.
no-renormalize
Disables the renormalize option. This overrides the
merge.renormalize configuration variable.
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.
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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.renormalize
Tell git that canonical representation of files in the reposi-
tory has changed over time (e.g. earlier commits record text
files with CRLF line endings, but recent ones use LF line end-
ings). 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 resolution program is used by git-merge-
tool(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 corre-
sponding 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.
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GIT-MERGE(1)GIT-MERGE(1)
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 ALSOgit-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: mailto:gitster@pobox.com>
DOCUMENTATION
Documentation by Junio C Hamano and the git-list <git@vger.kernel.org:
mailto:git@vger.kernel.org>.
GIT
Part of the git(1) suite
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