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235 lines
8.1 KiB
235 lines
8.1 KiB
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>] <remote>... |
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'git merge' <msg> HEAD <remote>... |
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DESCRIPTION |
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----------- |
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This is the top-level interface to the merge machinery |
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which drives multiple merge strategy scripts. |
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The second syntax (<msg> `HEAD` <remote>) 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> <remote>`. |
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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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<remote>...:: |
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Other branch heads to merge into our branch. You need at |
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least one <remote>. Specifying more than one <remote> |
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obviously means you are trying an Octopus. |
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include::merge-strategies.txt[] |
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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'. |
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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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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, branch head or tag), and the index file must |
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match the tree of `HEAD` commit (i.e. the contents of the last commit) |
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when it starts out. In other words, `git diff --cached HEAD` must |
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report no changes. (One exception is when the changed index |
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entries are already in the same state that would result from |
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the merge anyway.) |
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Three kinds of merge can happen: |
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* The merged commit is already contained in `HEAD`. This is the |
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simplest case, called "Already up-to-date." |
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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 remote branch you are pulling from during the |
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merge (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 remote 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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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 remote 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 the |
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remote 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 the remote version. |
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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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