git-merge

GIT-MERGE(1)                      Git Manual                      GIT-MERGE(1)



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

SYNOPSIS
       git merge [-n] [--stat] [--no-commit] [--squash] [-s ]...
               [--[no-]rerere-autoupdate] [-m ] ...
       git merge  HEAD ...


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 ( HEAD ...) 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  ....

       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=
           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).

       --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.

       -X , --strategy-option=
           Pass merge strategy specific option through to the merge strategy.

       -m 
           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.

       ...
           Commits, usually other branch heads, to merge into our branch. You
           need at least one . Specifying more than one 
           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:

       ·   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 MERGE_HEAD versions.

       ·   Look at the diffs from each branch.  git log --merge -p  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 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..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..name
           Defines a human-readable name for a custom low-level merge driver.
           See gitattributes(5) for details.

       merge..driver
           Defines the command that implements a custom low-level merge
           driver. See gitattributes(5) for details.

       merge..recursive
           Names a low-level merge driver to be used when performing an
           internal merge between common ancestors. See gitattributes(5) for
           details.

       branch..mergeoptions
           Sets default options for merging into branch . 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 

DOCUMENTATION
       Documentation by Junio C Hamano and the git-list
       .

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



Git 1.7.0.4                       12/03/2010                      GIT-MERGE(1)