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>]
[--[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 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.
--edit, --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 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 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.
-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 commits being merged have good and
trusted GPG signatures and abort the merge in case they do not.
--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.
-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.
--[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, and if
merge.defaultToUpstream configuration variable is set, 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.
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 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. 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.
rename-threshold=<n>
Controls the similarity threshold used for rename
detection. See also
git-diff(1)-M.
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.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.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
•bc3
•codecompare
•deltawalker
•diffuse
•ecmerge
•emerge
•gvimdiff
•gvimdiff2
•kdiff3
•meld
•opendiff
•p4merge
•tkdiff
•tortoisemerge
•vimdiff
•vimdiff2
•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.