1git-merge(1) 2============ 3 4NAME 5---- 6git-merge - Join two or more development histories together 7 8 9SYNOPSIS 10-------- 11[verse] 12'git-merge' [-n] [--no-commit] [--squash] [-s <strategy>]... 13 -m=<msg> <remote> <remote>... 14 15DESCRIPTION 16----------- 17This is the top-level interface to the merge machinery 18which drives multiple merge strategy scripts. 19 20 21OPTIONS 22------- 23include::merge-options.txt[] 24 25<msg>:: 26 The commit message to be used for the merge commit (in case 27 it is created). The `git-fmt-merge-msg` script can be used 28 to give a good default for automated `git-merge` invocations. 29 30<head>:: 31 Our branch head commit. This has to be `HEAD`, so new 32 syntax does not require it 33 34<remote>:: 35 Other branch head merged into our branch. You need at 36 least one <remote>. Specifying more than one <remote> 37 obviously means you are trying an Octopus. 38 39include::merge-strategies.txt[] 40 41 42If you tried a merge which resulted in a complex conflicts and 43would want to start over, you can recover with 44gitlink:git-reset[1]. 45 46 47HOW MERGE WORKS 48--------------- 49 50A merge is always between the current `HEAD` and one or more 51remote branch heads, and the index file must exactly match the 52tree of `HEAD` commit (i.e. the contents of the last commit) when 53it happens. In other words, `git-diff --cached HEAD` must 54report no changes. 55 56[NOTE] 57This is a bit of lie. In certain special cases, your index are 58allowed to be different from the tree of `HEAD` commit. The most 59notable case is when your `HEAD` commit is already ahead of what 60is being merged, in which case your index can have arbitrary 61difference from your `HEAD` commit. Otherwise, your index entries 62are allowed have differences from your `HEAD` commit that match 63the result of trivial merge (e.g. you received the same patch 64from external source to produce the same result as what you are 65merging). For example, if a path did not exist in the common 66ancestor and your head commit but exists in the tree you are 67merging into your repository, and if you already happen to have 68that path exactly in your index, the merge does not have to 69fail. 70 71Otherwise, merge will refuse to do any harm to your repository 72(that is, it may fetch the objects from remote, and it may even 73update the local branch used to keep track of the remote branch 74with `git pull remote rbranch:lbranch`, but your working tree, 75`.git/HEAD` pointer and index file are left intact). 76 77You may have local modifications in the working tree files. In 78other words, `git-diff` is allowed to report changes. 79However, the merge uses your working tree as the working area, 80and in order to prevent the merge operation from losing such 81changes, it makes sure that they do not interfere with the 82merge. Those complex tables in read-tree documentation define 83what it means for a path to "interfere with the merge". And if 84your local modifications interfere with the merge, again, it 85stops before touching anything. 86 87So in the above two "failed merge" case, you do not have to 88worry about loss of data --- you simply were not ready to do 89a merge, so no merge happened at all. You may want to finish 90whatever you were in the middle of doing, and retry the same 91pull after you are done and ready. 92 93When things cleanly merge, these things happen: 94 951. the results are updated both in the index file and in your 96 working tree, 972. index file is written out as a tree, 983. the tree gets committed, and 994. the `HEAD` pointer gets advanced. 100 101Because of 2., we require that the original state of the index 102file to match exactly the current `HEAD` commit; otherwise we 103will write out your local changes already registered in your 104index file along with the merge result, which is not good. 105Because 1. involves only the paths different between your 106branch and the remote branch you are pulling from during the 107merge (which is typically a fraction of the whole tree), you can 108have local modifications in your working tree as long as they do 109not overlap with what the merge updates. 110 111When there are conflicts, these things happen: 112 1131. `HEAD` stays the same. 114 1152. Cleanly merged paths are updated both in the index file and 116 in your working tree. 117 1183. For conflicting paths, the index file records up to three 119 versions; stage1 stores the version from the common ancestor, 120 stage2 from `HEAD`, and stage3 from the remote branch (you 121 can inspect the stages with `git-ls-files -u`). The working 122 tree files have the result of "merge" program; i.e. 3-way 123 merge result with familiar conflict markers `<<< === >>>`. 124 1254. No other changes are done. In particular, the local 126 modifications you had before you started merge will stay the 127 same and the index entries for them stay as they were, 128 i.e. matching `HEAD`. 129 130After seeing a conflict, you can do two things: 131 132 * Decide not to merge. The only clean-up you need are to reset 133 the index file to the `HEAD` commit to reverse 2. and to clean 134 up working tree changes made by 2. and 3.; `git-reset` can 135 be used for this. 136 137 * Resolve the conflicts. `git-diff` would report only the 138 conflicting paths because of the above 2. and 3.. Edit the 139 working tree files into a desirable shape, `git-update-index` 140 them, to make the index file contain what the merge result 141 should be, and run `git-commit` to commit the result. 142 143 144SEE ALSO 145-------- 146gitlink:git-fmt-merge-msg[1], gitlink:git-pull[1] 147 148 149Author 150------ 151Written by Junio C Hamano <junkio@cox.net> 152 153 154Documentation 155-------------- 156Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. 157 158GIT 159--- 160Part of the gitlink:git[7] suite