1git-merge(1) 2============ 3 4NAME 5---- 6git-merge - Grand Unified Merge Driver 7 8 9SYNOPSIS 10-------- 11'git-merge' [-n] [--no-commit] [-s <strategy>]... <msg> <head> <remote> <remote>... 12 13 14DESCRIPTION 15----------- 16This is the top-level user interface to the merge machinery 17which drives multiple merge strategy scripts. 18 19 20OPTIONS 21------- 22include::merge-options.txt[] 23 24<msg>:: 25 The commit message to be used for the merge commit (in case 26 it is created). The `git-fmt-merge-msg` script can be used 27 to give a good default for automated `git-merge` invocations. 28 29<head>:: 30 our branch head commit. 31 32<remote>:: 33 other branch head merged into our branch. You need at 34 least one <remote>. Specifying more than one <remote> 35 obviously means you are trying an Octopus. 36 37include::merge-strategies.txt[] 38 39 40HOW MERGE WORKS 41--------------- 42 43A merge is always between the current `HEAD` and one or more 44remote branch heads, and the index file must exactly match the 45tree of `HEAD` commit (i.e. the contents of the last commit) when 46it happens. In other words, `git-diff --cached HEAD` must 47report no changes. 48 49[NOTE] 50This is a bit of lie. In certain special cases, your index are 51allowed to be different from the tree of `HEAD` commit. The most 52notable case is when your `HEAD` commit is already ahead of what 53is being merged, in which case your index can have arbitrary 54difference from your `HEAD` commit. Otherwise, your index entries 55are allowed have differences from your `HEAD` commit that match 56the result of trivial merge (e.g. you received the same patch 57from external source to produce the same result as what you are 58merging). For example, if a path did not exist in the common 59ancestor and your head commit but exists in the tree you are 60merging into your repository, and if you already happen to have 61that path exactly in your index, the merge does not have to 62fail. 63 64Otherwise, merge will refuse to do any harm to your repository 65(that is, it may fetch the objects from remote, and it may even 66update the local branch used to keep track of the remote branch 67with `git pull remote rbranch:lbranch`, but your working tree, 68`.git/HEAD` pointer and index file are left intact). 69 70You may have local modifications in the working tree files. In 71other words, `git-diff` is allowed to report changes. 72However, the merge uses your working tree as the working area, 73and in order to prevent the merge operation from losing such 74changes, it makes sure that they do not interfere with the 75merge. Those complex tables in read-tree documentation define 76what it means for a path to "interfere with the merge". And if 77your local modifications interfere with the merge, again, it 78stops before touching anything. 79 80So in the above two "failed merge" case, you do not have to 81worry about lossage of data --- you simply were not ready to do 82a merge, so no merge happened at all. You may want to finish 83whatever you were in the middle of doing, and retry the same 84pull after you are done and ready. 85 86When things cleanly merge, these things happen: 87 881. the results are updated both in the index file and in your 89 working tree, 902. index file is written out as a tree, 913. the tree gets committed, and 924. the `HEAD` pointer gets advanced. 93 94Because of 2., we require that the original state of the index 95file to match exactly the current `HEAD` commit; otherwise we 96will write out your local changes already registered in your 97index file along with the merge result, which is not good. 98Because 1. involves only the paths different between your 99branch and the remote branch you are pulling from during the 100merge (which is typically a fraction of the whole tree), you can 101have local modifications in your working tree as long as they do 102not overlap with what the merge updates. 103 104When there are conflicts, these things happen: 105 1061. `HEAD` stays the same. 107 1082. Cleanly merged paths are updated both in the index file and 109 in your working tree. 110 1113. For conflicting paths, the index file records up to three 112 versions; stage1 stores the version from the common ancestor, 113 stage2 from `HEAD`, and stage3 from the remote branch (you 114 can inspect the stages with `git-ls-files -u`). The working 115 tree files have the result of "merge" program; i.e. 3-way 116 merge result with familiar conflict markers `<<< === >>>`. 117 1184. No other changes are done. In particular, the local 119 modifications you had before you started merge will stay the 120 same and the index entries for them stay as they were, 121 i.e. matching `HEAD`. 122 123After seeing a conflict, you can do two things: 124 125 * Decide not to merge. The only clean-up you need are to reset 126 the index file to the `HEAD` commit to reverse 2. and to clean 127 up working tree changes made by 2. and 3.; `git-reset` can 128 be used for this. 129 130 * Resolve the conflicts. `git-diff` would report only the 131 conflicting paths because of the above 2. and 3.. Edit the 132 working tree files into a desirable shape, `git-update-index` 133 them, to make the index file contain what the merge result 134 should be, and run `git-commit` to commit the result. 135 136 137SEE ALSO 138-------- 139gitlink:git-fmt-merge-msg[1], gitlink:git-pull[1] 140 141 142Author 143------ 144Written by Junio C Hamano <junkio@cox.net> 145 146 147Documentation 148-------------- 149Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. 150 151GIT 152--- 153Part of the gitlink:git[7] suite