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 40If you tried a merge which resulted in a complex conflicts and 41would want to start over, you can recover with 42gitlink:git-reset[1]. 43 44 45HOW MERGE WORKS 46--------------- 47 48A merge is always between the current `HEAD` and one or more 49remote branch heads, and the index file must exactly match the 50tree of `HEAD` commit (i.e. the contents of the last commit) when 51it happens. In other words, `git-diff --cached HEAD` must 52report no changes. 53 54[NOTE] 55This is a bit of lie. In certain special cases, your index are 56allowed to be different from the tree of `HEAD` commit. The most 57notable case is when your `HEAD` commit is already ahead of what 58is being merged, in which case your index can have arbitrary 59difference from your `HEAD` commit. Otherwise, your index entries 60are allowed have differences from your `HEAD` commit that match 61the result of trivial merge (e.g. you received the same patch 62from external source to produce the same result as what you are 63merging). For example, if a path did not exist in the common 64ancestor and your head commit but exists in the tree you are 65merging into your repository, and if you already happen to have 66that path exactly in your index, the merge does not have to 67fail. 68 69Otherwise, merge will refuse to do any harm to your repository 70(that is, it may fetch the objects from remote, and it may even 71update the local branch used to keep track of the remote branch 72with `git pull remote rbranch:lbranch`, but your working tree, 73`.git/HEAD` pointer and index file are left intact). 74 75You may have local modifications in the working tree files. In 76other words, `git-diff` is allowed to report changes. 77However, the merge uses your working tree as the working area, 78and in order to prevent the merge operation from losing such 79changes, it makes sure that they do not interfere with the 80merge. Those complex tables in read-tree documentation define 81what it means for a path to "interfere with the merge". And if 82your local modifications interfere with the merge, again, it 83stops before touching anything. 84 85So in the above two "failed merge" case, you do not have to 86worry about loss of data --- you simply were not ready to do 87a merge, so no merge happened at all. You may want to finish 88whatever you were in the middle of doing, and retry the same 89pull after you are done and ready. 90 91When things cleanly merge, these things happen: 92 931. the results are updated both in the index file and in your 94 working tree, 952. index file is written out as a tree, 963. the tree gets committed, and 974. the `HEAD` pointer gets advanced. 98 99Because of 2., we require that the original state of the index 100file to match exactly the current `HEAD` commit; otherwise we 101will write out your local changes already registered in your 102index file along with the merge result, which is not good. 103Because 1. involves only the paths different between your 104branch and the remote branch you are pulling from during the 105merge (which is typically a fraction of the whole tree), you can 106have local modifications in your working tree as long as they do 107not overlap with what the merge updates. 108 109When there are conflicts, these things happen: 110 1111. `HEAD` stays the same. 112 1132. Cleanly merged paths are updated both in the index file and 114 in your working tree. 115 1163. For conflicting paths, the index file records up to three 117 versions; stage1 stores the version from the common ancestor, 118 stage2 from `HEAD`, and stage3 from the remote branch (you 119 can inspect the stages with `git-ls-files -u`). The working 120 tree files have the result of "merge" program; i.e. 3-way 121 merge result with familiar conflict markers `<<< === >>>`. 122 1234. No other changes are done. In particular, the local 124 modifications you had before you started merge will stay the 125 same and the index entries for them stay as they were, 126 i.e. matching `HEAD`. 127 128After seeing a conflict, you can do two things: 129 130 * Decide not to merge. The only clean-up you need are to reset 131 the index file to the `HEAD` commit to reverse 2. and to clean 132 up working tree changes made by 2. and 3.; `git-reset` can 133 be used for this. 134 135 * Resolve the conflicts. `git-diff` would report only the 136 conflicting paths because of the above 2. and 3.. Edit the 137 working tree files into a desirable shape, `git-update-index` 138 them, to make the index file contain what the merge result 139 should be, and run `git-commit` to commit the result. 140 141 142SEE ALSO 143-------- 144gitlink:git-fmt-merge-msg[1], gitlink:git-pull[1] 145 146 147Author 148------ 149Written by Junio C Hamano <junkio@cox.net> 150 151 152Documentation 153-------------- 154Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. 155 156GIT 157--- 158Part of the gitlink:git[7] suite