30f2bade84
A merge-based operation in git can fail in two ways: one that stops before touching anything, or one that goes ahead and results in conflicts. As the 'git merge' manual explains: | 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. Unfortunately, the placement of this sentence makes it easy to skip over, and its formulation leaves the important point, that any other attempted merge will be gracefully aborted, unspoken. So give this point its own section and expand upon it. Probably this could be simplified somewhat: after all, a change registered in the index is just a special kind of local uncommited change, so the second added paragraph is only a special case of the first. It seemed more helpful to be explicit here. Inspired by <http://gitster.livejournal.com/25801.html>. Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Thomas Rast <trast@student.ethz.ch>
308 lines
10 KiB
Plaintext
308 lines
10 KiB
Plaintext
git-merge(1)
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============
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NAME
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----
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git-merge - Join two or more development histories together
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SYNOPSIS
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--------
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[verse]
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'git merge' [-n] [--stat] [--no-commit] [--squash] [-s <strategy>]...
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[-m <msg>] <commit>...
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'git merge' <msg> HEAD <commit>...
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DESCRIPTION
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-----------
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Incorporates changes from the named commits (since the time their
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histories diverged from the current branch) into the current
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branch. This command is used by 'git pull' to incorporate changes
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from another repository and can be used by hand to merge changes
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from one branch into another.
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Assume the following history exists and the current branch is
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"`master`":
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------------
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A---B---C topic
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/
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D---E---F---G master
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------------
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Then "`git merge topic`" will replay the changes made on the
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`topic` branch since it diverged from `master` (i.e., `E`) until
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its current commit (`C`) on top of `master`, and record the result
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in a new commit along with the names of the two parent commits and
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a log message from the user describing the changes.
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------------
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A---B---C topic
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/ \
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D---E---F---G---H master
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------------
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The second syntax (<msg> `HEAD` <commit>...) is supported for
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historical reasons. Do not use it from the command line or in
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new scripts. It is the same as `git merge -m <msg> <commit>...`.
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*Warning*: Running 'git merge' with uncommitted changes is
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discouraged: while possible, it leaves you in a state that is hard to
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back out of in the case of a conflict.
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OPTIONS
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-------
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include::merge-options.txt[]
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-m <msg>::
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Set the commit message to be used for the merge commit (in
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case one is created). The 'git fmt-merge-msg' command can be
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used to give a good default for automated 'git merge'
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invocations.
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<commit>...::
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Commits, usually other branch heads, to merge into our branch.
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You need at least one <commit>. Specifying more than one
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<commit> obviously means you are trying an Octopus.
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PRE-MERGE CHECKS
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----------------
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Before applying outside changes, you should get your own work in
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good shape and committed locally, so it will not be clobbered if
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there are conflicts. See also linkgit:git-stash[1].
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'git pull' and 'git merge' will stop without doing anything when
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local uncommitted changes overlap with files that 'git pull'/'git
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merge' may need to update.
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To avoid recording unrelated changes in the merge commit,
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'git pull' and 'git merge' will also abort if there are any changes
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registered in the index relative to the `HEAD` commit. (One
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exception is when the changed index entries are in the state that
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would result from the merge already.)
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If all named commits are already ancestors of `HEAD`, 'git merge'
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will exit early with the message "Already up-to-date."
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HOW MERGE WORKS
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---------------
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A merge is always between the current `HEAD` and one or more
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commits (usually a branch head or tag).
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Two kinds of merge can happen:
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* `HEAD` is already contained in the merged commit. This is the
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most common case especially when invoked from 'git pull':
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you are tracking an upstream repository, have committed no local
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changes and now you want to update to a newer upstream revision.
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Your `HEAD` (and the index) is updated to point at the merged
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commit, without creating an extra merge commit. This is
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called "Fast-forward".
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* Both the merged commit and `HEAD` are independent and must be
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tied together by a merge commit that has both of them as its parents.
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The rest of this section describes this "True merge" case.
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The chosen merge strategy merges the two commits into a single
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new source tree.
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When things merge cleanly, this is what happens:
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1. The results are updated both in the index file and in your
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working tree;
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2. Index file is written out as a tree;
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3. The tree gets committed; and
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4. The `HEAD` pointer gets advanced.
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Because of 2., we require that the original state of the index
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file matches exactly the current `HEAD` commit; otherwise we
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will write out your local changes already registered in your
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index file along with the merge result, which is not good.
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Because 1. involves only those paths differing between your
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branch and the branch you are merging
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(which is typically a fraction of the whole tree), you can
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have local modifications in your working tree as long as they do
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not overlap with what the merge updates.
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When there are conflicts, the following happens:
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1. `HEAD` stays the same.
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2. Cleanly merged paths are updated both in the index file and
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in your working tree.
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3. For conflicting paths, the index file records up to three
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versions; stage1 stores the version from the common ancestor,
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stage2 from `HEAD`, and stage3 from the other branch (you
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can inspect the stages with `git ls-files -u`). The working
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tree files contain the result of the "merge" program; i.e. 3-way
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merge results with familiar conflict markers `<<< === >>>`.
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4. No other changes are done. In particular, the local
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modifications you had before you started merge will stay the
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same and the index entries for them stay as they were,
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i.e. matching `HEAD`.
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If you tried a merge which resulted in complex conflicts and
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want to start over, you can recover with `git reset --merge`.
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HOW CONFLICTS ARE PRESENTED
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---------------------------
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During a merge, the working tree files are updated to reflect the result
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of the merge. Among the changes made to the common ancestor's version,
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non-overlapping ones (that is, you changed an area of the file while the
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other side left that area intact, or vice versa) are incorporated in the
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final result verbatim. When both sides made changes to the same area,
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however, git cannot randomly pick one side over the other, and asks you to
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resolve it by leaving what both sides did to that area.
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By default, git uses the same style as that is used by "merge" program
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from the RCS suite to present such a conflicted hunk, like this:
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------------
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Here are lines that are either unchanged from the common
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ancestor, or cleanly resolved because only one side changed.
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<<<<<<< yours:sample.txt
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Conflict resolution is hard;
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let's go shopping.
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=======
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Git makes conflict resolution easy.
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>>>>>>> theirs:sample.txt
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And here is another line that is cleanly resolved or unmodified.
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------------
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The area where a pair of conflicting changes happened is marked with markers
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`<<<<<<<`, `=======`, and `>>>>>>>`. The part before the `=======`
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is typically your side, and the part afterwards is typically their side.
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The default format does not show what the original said in the conflicting
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area. You cannot tell how many lines are deleted and replaced with
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Barbie's remark on your side. The only thing you can tell is that your
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side wants to say it is hard and you'd prefer to go shopping, while the
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other side wants to claim it is easy.
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An alternative style can be used by setting the "merge.conflictstyle"
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configuration variable to "diff3". In "diff3" style, the above conflict
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may look like this:
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------------
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Here are lines that are either unchanged from the common
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ancestor, or cleanly resolved because only one side changed.
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<<<<<<< yours:sample.txt
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Conflict resolution is hard;
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let's go shopping.
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|||||||
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Conflict resolution is hard.
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=======
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Git makes conflict resolution easy.
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>>>>>>> theirs:sample.txt
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And here is another line that is cleanly resolved or unmodified.
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------------
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In addition to the `<<<<<<<`, `=======`, and `>>>>>>>` markers, it uses
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another `|||||||` marker that is followed by the original text. You can
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tell that the original just stated a fact, and your side simply gave in to
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that statement and gave up, while the other side tried to have a more
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positive attitude. You can sometimes come up with a better resolution by
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viewing the original.
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HOW TO RESOLVE CONFLICTS
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------------------------
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After seeing a conflict, you can do two things:
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* Decide not to merge. The only clean-ups you need are to reset
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the index file to the `HEAD` commit to reverse 2. and to clean
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up working tree changes made by 2. and 3.; `git-reset --hard` can
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be used for this.
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* Resolve the conflicts. Git will mark the conflicts in
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the working tree. Edit the files into shape and
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'git add' them to the index. Use 'git commit' to seal the deal.
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You can work through the conflict with a number of tools:
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* Use a mergetool. `git mergetool` to launch a graphical
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mergetool which will work you through the merge.
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* Look at the diffs. `git diff` will show a three-way diff,
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highlighting changes from both the HEAD and their versions.
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* Look at the diffs on their own. `git log --merge -p <path>`
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will show diffs first for the HEAD version and then
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their version.
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* Look at the originals. `git show :1:filename` shows the
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common ancestor, `git show :2:filename` shows the HEAD
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version and `git show :3:filename` shows their version.
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EXAMPLES
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--------
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* Merge branches `fixes` and `enhancements` on top of
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the current branch, making an octopus merge:
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+
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------------------------------------------------
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$ git merge fixes enhancements
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------------------------------------------------
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* Merge branch `obsolete` into the current branch, using `ours`
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merge strategy:
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+
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------------------------------------------------
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$ git merge -s ours obsolete
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------------------------------------------------
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* Merge branch `maint` into the current branch, but do not make
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a new commit automatically:
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+
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------------------------------------------------
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$ git merge --no-commit maint
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------------------------------------------------
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+
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This can be used when you want to include further changes to the
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merge, or want to write your own merge commit message.
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+
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You should refrain from abusing this option to sneak substantial
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changes into a merge commit. Small fixups like bumping
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release/version name would be acceptable.
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include::merge-strategies.txt[]
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CONFIGURATION
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-------------
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include::merge-config.txt[]
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branch.<name>.mergeoptions::
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Sets default options for merging into branch <name>. The syntax and
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supported options are the same as those of 'git merge', but option
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values containing whitespace characters are currently not supported.
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SEE ALSO
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--------
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linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],
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linkgit:gitattributes[5],
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linkgit:git-reset[1],
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linkgit:git-diff[1], linkgit:git-ls-files[1],
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linkgit:git-add[1], linkgit:git-rm[1],
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linkgit:git-mergetool[1]
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Author
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------
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Written by Junio C Hamano <gitster@pobox.com>
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Documentation
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--------------
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Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
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GIT
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---
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Part of the linkgit:git[1] suite
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