git-merge(1) ============ NAME ---- git-merge - Grand Unified Merge Driver SYNOPSIS -------- 'git-merge' [-n] [--no-commit] [-s ]... ... DESCRIPTION ----------- This is the top-level user interface to the merge machinery which drives multiple merge strategy scripts. OPTIONS ------- include::merge-options.txt[] :: 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. :: our branch head commit. :: other branch head merged into our branch. You need at least one . Specifying more than one obviously means you are trying an Octopus. include::merge-strategies.txt[] If you tried a merge which resulted in a complex conflicts and would want to start over, you can recover with gitlink:git-reset[1]. HOW MERGE WORKS --------------- A merge is always between the current `HEAD` and one or more remote branch heads, and the index file must exactly match the tree of `HEAD` commit (i.e. the contents of the last commit) when it happens. In other words, `git-diff --cached HEAD` must report no changes. [NOTE] This is a bit of lie. In certain special cases, your index are allowed to be different from the tree of `HEAD` commit. The most notable case is when your `HEAD` commit is already ahead of what is being merged, in which case your index can have arbitrary difference from your `HEAD` commit. Otherwise, your index entries are allowed have differences from your `HEAD` commit that match the result of trivial merge (e.g. you received the same patch from external source to produce the same result as what you are merging). For example, if a path did not exist in the common ancestor and your head commit but exists in the tree you are merging into your repository, and if you already happen to have that path exactly in your index, the merge does not have to fail. Otherwise, merge will refuse to do any harm to your repository (that is, it may fetch the objects from remote, and it may even update the local branch used to keep track of the remote branch with `git pull remote rbranch:lbranch`, but your working tree, `.git/HEAD` pointer and index file are left intact). You may have local modifications in the working tree files. In other words, `git-diff` is allowed to report changes. However, the merge uses your working tree as the working area, and in order to prevent the merge operation from losing such changes, it makes sure that they do not interfere with the merge. Those complex tables in read-tree documentation define what it means for a path to "interfere with the merge". And if your local modifications interfere with the merge, again, it stops before touching anything. So in the above two "failed merge" case, you do not have to worry about lossage of data --- you simply were not ready to do a merge, so no merge happened at all. You may want to finish whatever you were in the middle of doing, and retry the same pull after you are done and ready. When things cleanly merge, these things happen: 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 to match 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 the paths different 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, these things happen: 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 have the result of "merge" program; i.e. 3-way merge result 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`. After seeing a conflict, you can do two things: * Decide not to merge. The only clean-up 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` can be used for this. * Resolve the conflicts. `git-diff` would report only the conflicting paths because of the above 2. and 3.. Edit the working tree files into a desirable shape, `git-update-index` them, to make the index file contain what the merge result should be, and run `git-commit` to commit the result. SEE ALSO -------- gitlink:git-fmt-merge-msg[1], gitlink:git-pull[1] Author ------ Written by Junio C Hamano Documentation -------------- Documentation by Junio C Hamano and the git-list . GIT --- Part of the gitlink:git[7] suite