1git-merge(1) 2============ 3 4NAME 5---- 6git-merge - Grand Unified Merge Driver 7 8 9SYNOPSIS 10-------- 11[verse] 12'git-merge' [-n] [--no-commit] [--squash] [-s <strategy>]... 13 [--reflog-action=<action>] 14 -m=<msg> <remote> <remote>... 15 16DESCRIPTION 17----------- 18This is the top-level interface to the merge machinery 19which drives multiple merge strategy scripts. 20 21 22OPTIONS 23------- 24include::merge-options.txt[] 25 26<msg>:: 27 The commit message to be used for the merge commit (in case 28 it is created). The `git-fmt-merge-msg` script can be used 29 to give a good default for automated `git-merge` invocations. 30 31<head>:: 32 Our branch head commit. This has to be `HEAD`, so new 33 syntax does not require it 34 35<remote>:: 36 Other branch head merged into our branch. You need at 37 least one <remote>. Specifying more than one <remote> 38 obviously means you are trying an Octopus. 39 40--reflog-action=<action>:: 41 This is used internally when `git-pull` calls this command 42 to record that the merge was created by `pull` command 43 in the `ref-log` entry that results from the merge. 44 45include::merge-strategies.txt[] 46 47 48If you tried a merge which resulted in a complex conflicts and 49would want to start over, you can recover with 50gitlink:git-reset[1]. 51 52 53HOW MERGE WORKS 54--------------- 55 56A merge is always between the current `HEAD` and one or more 57remote branch heads, and the index file must exactly match the 58tree of `HEAD` commit (i.e. the contents of the last commit) when 59it happens. In other words, `git-diff --cached HEAD` must 60report no changes. 61 62[NOTE] 63This is a bit of lie. In certain special cases, your index are 64allowed to be different from the tree of `HEAD` commit. The most 65notable case is when your `HEAD` commit is already ahead of what 66is being merged, in which case your index can have arbitrary 67difference from your `HEAD` commit. Otherwise, your index entries 68are allowed have differences from your `HEAD` commit that match 69the result of trivial merge (e.g. you received the same patch 70from external source to produce the same result as what you are 71merging). For example, if a path did not exist in the common 72ancestor and your head commit but exists in the tree you are 73merging into your repository, and if you already happen to have 74that path exactly in your index, the merge does not have to 75fail. 76 77Otherwise, merge will refuse to do any harm to your repository 78(that is, it may fetch the objects from remote, and it may even 79update the local branch used to keep track of the remote branch 80with `git pull remote rbranch:lbranch`, but your working tree, 81`.git/HEAD` pointer and index file are left intact). 82 83You may have local modifications in the working tree files. In 84other words, `git-diff` is allowed to report changes. 85However, the merge uses your working tree as the working area, 86and in order to prevent the merge operation from losing such 87changes, it makes sure that they do not interfere with the 88merge. Those complex tables in read-tree documentation define 89what it means for a path to "interfere with the merge". And if 90your local modifications interfere with the merge, again, it 91stops before touching anything. 92 93So in the above two "failed merge" case, you do not have to 94worry about loss of data --- you simply were not ready to do 95a merge, so no merge happened at all. You may want to finish 96whatever you were in the middle of doing, and retry the same 97pull after you are done and ready. 98 99When things cleanly merge, these things happen: 100 1011. the results are updated both in the index file and in your 102 working tree, 1032. index file is written out as a tree, 1043. the tree gets committed, and 1054. the `HEAD` pointer gets advanced. 106 107Because of 2., we require that the original state of the index 108file to match exactly the current `HEAD` commit; otherwise we 109will write out your local changes already registered in your 110index file along with the merge result, which is not good. 111Because 1. involves only the paths different between your 112branch and the remote branch you are pulling from during the 113merge (which is typically a fraction of the whole tree), you can 114have local modifications in your working tree as long as they do 115not overlap with what the merge updates. 116 117When there are conflicts, these things happen: 118 1191. `HEAD` stays the same. 120 1212. Cleanly merged paths are updated both in the index file and 122 in your working tree. 123 1243. For conflicting paths, the index file records up to three 125 versions; stage1 stores the version from the common ancestor, 126 stage2 from `HEAD`, and stage3 from the remote branch (you 127 can inspect the stages with `git-ls-files -u`). The working 128 tree files have the result of "merge" program; i.e. 3-way 129 merge result with familiar conflict markers `<<< === >>>`. 130 1314. No other changes are done. In particular, the local 132 modifications you had before you started merge will stay the 133 same and the index entries for them stay as they were, 134 i.e. matching `HEAD`. 135 136After seeing a conflict, you can do two things: 137 138 * Decide not to merge. The only clean-up you need are to reset 139 the index file to the `HEAD` commit to reverse 2. and to clean 140 up working tree changes made by 2. and 3.; `git-reset` can 141 be used for this. 142 143 * Resolve the conflicts. `git-diff` would report only the 144 conflicting paths because of the above 2. and 3.. Edit the 145 working tree files into a desirable shape, `git-update-index` 146 them, to make the index file contain what the merge result 147 should be, and run `git-commit` to commit the result. 148 149 150SEE ALSO 151-------- 152gitlink:git-fmt-merge-msg[1], gitlink:git-pull[1] 153 154 155Author 156------ 157Written by Junio C Hamano <junkio@cox.net> 158 159 160Documentation 161-------------- 162Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. 163 164GIT 165--- 166Part of the gitlink:git[7] suite