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:
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:
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
version.
o 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
o Merge branches fixes and enhancements on top of the current branch,
making an octopus merge:
$ git merge fixes enhancements
o Merge branch obsolete into the current branch, using ours merge
strategy:
$ git merge -s ours obsolete
o 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[1]>
DOCUMENTATION
Documentation by Junio C Hamano and the git-list
<git@vger.kernel.org[2]>.
GIT
Part of the git(1) suite
NOTES
1. gitster@pobox.com
mailto:gitster@pobox.com
2. git@vger.kernel.org
mailto:git@vger.kernel.org