--------
[verse]
'git merge' [-n] [--stat] [--no-commit] [--squash] [-s <strategy>]...
- [-m <msg>] <commit>...
+ [--[no-]rerere-autoupdate] [-m <msg>] <commit>...
'git merge' <msg> HEAD <commit>...
DESCRIPTION
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.
-HOW MERGE WORKS
----------------
+PRE-MERGE CHECKS
+----------------
-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.)
+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 linkgit: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.
-Three kinds of merge can happen:
+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.)
-* The merged commit is already contained in `HEAD`. This is the
- simplest case, called "Already up-to-date."
+If all named commits are already ancestors of `HEAD`, 'git merge'
+will exit early with the message "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".
+FAST-FORWARD MERGE
+------------------
-* 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.
+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.
-The chosen merge strategy merges the two commits into a single
-new source tree.
-When things merge cleanly, this is what happens:
+This behavior can be suppressed with the `--no-ff` option.
-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.
+TRUE MERGE
+----------
-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 branch you are merging
-(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.
+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.
-When there are conflicts, the following happens:
+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.
-1. `HEAD` stays the same.
+When it is not obvious how to reconcile the changes, the following
+happens:
-2. Cleanly merged paths are updated both in the index file and
+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.
-
-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 other branch (you
+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 `<<< === >>>`.
-
-4. No other changes are done. In particular, the local
+ 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`.
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 their versions.
+ highlighting changes from both the `HEAD` and `MERGE_HEAD`
+ versions.
- * Look at the diffs
on their own. `git log --merge -p <path>`
- will show diffs first for the HEAD version and then
- their version.
+ * 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 their version.
+ common ancestor, `git show :2:filename` shows the `HEAD`
+ version, and `git show :3:filename` shows the `MERGE_HEAD`
+ version.
EXAMPLES