Documentation/git-merge.txt - git - Git at Google

 git-merge(1)
 ============

 NAME
 ----
 git-merge - Join two or more development histories together


 SYNOPSIS
 --------
 [verse]
 'git merge' [-n] [--stat] [--no-commit] [--squash] [-s <strategy>]...
 	[-m <msg>] <remote> <remote>...
 'git merge' <msg> HEAD <remote>...

 DESCRIPTION
 -----------
 This is the top-level interface to the merge machinery
 which drives multiple merge strategy scripts.

 The second syntax (<msg> `HEAD` <remote>) 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> <remote>`.


 OPTIONS
 -------
 include::merge-options.txt[]

 -m <msg>::
 	The commit message to be used for the merge commit (in case
 	it is created). The 'git-fmt-merge-msg' script can be used
 	to give a good default for automated 'git-merge' invocations.

 <remote>...::
 	Other branch heads to merge into our branch.  You need at
 	least one <remote>.  Specifying more than one <remote>
 	obviously means you are trying an Octopus.

 include::merge-strategies.txt[]


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

 CONFIGURATION
 -------------
 include::merge-config.txt[]

 branch.<name>.mergeoptions::
 	Sets default options for merging into branch <name>. The syntax and
 	supported options are equal to that of 'git-merge', but option values
 	containing whitespace characters are currently not supported.

 HOW MERGE WORKS
 ---------------

 A merge is always between the current `HEAD` and one or more
 commits (usually, branch head or tag), and the index file must
 match the tree of `HEAD` commit (i.e. the contents of the last commit)
 when it starts out.  In other words, `git diff --cached HEAD` must
 report no changes.  (One exception is when the changed index
 entries are already in the same state that would result from
 the merge anyway.)

 Three kinds of merge can happen:

 * The merged commit is already contained in `HEAD`. This is the
   simplest case, called "Already up-to-date."

 * `HEAD` is already contained in the merged commit. This is the
   most common case especially when invoked from 'git pull':
   you are tracking an upstream repository, have committed no local
   changes and now you want to update to a newer upstream revision.
   Your `HEAD` (and the index) is updated to point at the merged
   commit, without creating an extra merge commit.  This is
   called "Fast-forward".

 * Both the merged commit and `HEAD` are independent and must be
   tied together by a merge commit that has both of them as its parents.
   The rest of this section describes this "True merge" case.

 The chosen merge strategy merges the two commits into a single
 new source tree.
 When things merge cleanly, this is what happens:

 1. The results are updated both in the index file and in your
    working tree;
 2. Index file is written out as a tree;
 3. The tree gets committed; and
 4. The `HEAD` pointer gets advanced.

 Because of 2., we require that the original state of the index
 file matches exactly the current `HEAD` commit; otherwise we
 will write out your local changes already registered in your
 index file along with the merge result, which is not good.
 Because 1. involves only those paths differing between your
 branch and the remote branch you are pulling from during the
 merge (which is typically a fraction of the whole tree), you can
 have local modifications in your working tree as long as they do
 not overlap with what the merge updates.

 When there are conflicts, the following happens:

 1. `HEAD` stays the same.

 2. Cleanly merged paths are updated both in the index file and
    in your working tree.

 3. For conflicting paths, the index file records up to three
    versions; stage1 stores the version from the common ancestor,
    stage2 from `HEAD`, and stage3 from the remote branch (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 `<<< === >>>`.

 4. No other changes are done.  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`.

 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:

  * 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.

  * 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 remote versions.

  * Look at the diffs on their own. 'git log --merge -p <path>'
    will show diffs first for the HEAD version and then the
    remote 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 remote version.

 SEE ALSO
 --------
 linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],
 linkgit:gitattributes[5],
 linkgit:git-reset[1],
 linkgit:git-diff[1], linkgit:git-ls-files[1],
 linkgit:git-add[1], linkgit:git-rm[1],
 linkgit:git-mergetool[1]

 Author
 ------
 Written by Junio C Hamano <gitster@pobox.com>


 Documentation
 --------------
 Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.

 GIT
 ---
 Part of the linkgit:git[1] suite
	git-merge(1)
	============

	NAME
	----
	git-merge - Join two or more development histories together


	SYNOPSIS
	--------
	[verse]
	'git merge' [-n] [--stat] [--no-commit] [--squash] [-s <strategy>]...
	[-m <msg>] <remote> <remote>...
	'git merge' <msg> HEAD <remote>...

	DESCRIPTION
	-----------
	This is the top-level interface to the merge machinery
	which drives multiple merge strategy scripts.

	The second syntax (<msg> `HEAD` <remote>) 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> <remote>`.


	OPTIONS
	-------
	include::merge-options.txt[]

	-m <msg>::
	The commit message to be used for the merge commit (in case
	it is created). The 'git-fmt-merge-msg' script can be used
	to give a good default for automated 'git-merge' invocations.

	<remote>...::
	Other branch heads to merge into our branch. You need at
	least one <remote>. Specifying more than one <remote>
	obviously means you are trying an Octopus.

	include::merge-strategies.txt[]


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

	CONFIGURATION
	-------------
	include::merge-config.txt[]

	branch.<name>.mergeoptions::
	Sets default options for merging into branch <name>. The syntax and
	supported options are equal to that of 'git-merge', but option values
	containing whitespace characters are currently not supported.

	HOW MERGE WORKS
	---------------

	A merge is always between the current `HEAD` and one or more
	commits (usually, branch head or tag), and the index file must
	match the tree of `HEAD` commit (i.e. the contents of the last commit)
	when it starts out. In other words, `git diff --cached HEAD` must
	report no changes. (One exception is when the changed index
	entries are already in the same state that would result from
	the merge anyway.)

	Three kinds of merge can happen:

	* The merged commit is already contained in `HEAD`. This is the
	simplest case, called "Already up-to-date."

	* `HEAD` is already contained in the merged commit. This is the
	most common case especially when invoked from 'git pull':
	you are tracking an upstream repository, have committed no local
	changes and now you want to update to a newer upstream revision.
	Your `HEAD` (and the index) is updated to point at the merged
	commit, without creating an extra merge commit. This is
	called "Fast-forward".

	* Both the merged commit and `HEAD` are independent and must be
	tied together by a merge commit that has both of them as its parents.
	The rest of this section describes this "True merge" case.

	The chosen merge strategy merges the two commits into a single
	new source tree.
	When things merge cleanly, this is what happens:

	1. The results are updated both in the index file and in your
	working tree;
	2. Index file is written out as a tree;
	3. The tree gets committed; and
	4. The `HEAD` pointer gets advanced.

	Because of 2., we require that the original state of the index
	file matches exactly the current `HEAD` commit; otherwise we
	will write out your local changes already registered in your
	index file along with the merge result, which is not good.
	Because 1. involves only those paths differing between your
	branch and the remote branch you are pulling from during the
	merge (which is typically a fraction of the whole tree), you can
	have local modifications in your working tree as long as they do
	not overlap with what the merge updates.

	When there are conflicts, the following happens:

	1. `HEAD` stays the same.

	2. Cleanly merged paths are updated both in the index file and
	in your working tree.

	3. For conflicting paths, the index file records up to three
	versions; stage1 stores the version from the common ancestor,
	stage2 from `HEAD`, and stage3 from the remote branch (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 `<<< === >>>`.

	4. No other changes are done. 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`.

	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:

	* 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.

	* 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 remote versions.

	* Look at the diffs on their own. 'git log --merge -p <path>'
	will show diffs first for the HEAD version and then the
	remote 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 remote version.

	SEE ALSO
	--------
	linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],
	linkgit:gitattributes[5],
	linkgit:git-reset[1],
	linkgit:git-diff[1], linkgit:git-ls-files[1],
	linkgit:git-add[1], linkgit:git-rm[1],
	linkgit:git-mergetool[1]

	Author
	------
	Written by Junio C Hamano <gitster@pobox.com>


	Documentation
	--------------
	Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.

	GIT
	---
	Part of the linkgit:git[1] suite