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] [--summary] [--no-commit] [--squash] [-s <strategy>]... 13 [-m <msg>] <remote> <remote>... 14'git-merge' <msg> HEAD <remote>... 15 16DESCRIPTION 17----------- 18This is the top-level interface to the merge machinery 19which drives multiple merge strategy scripts. 20 21The second syntax (<msg> `HEAD` <remote>) is supported for 22historical reasons. Do not use it from the command line or in 23new scripts. It is the same as `git merge -m <msg> <remote>`. 24 25 26OPTIONS 27------- 28include::merge-options.txt[] 29 30-m <msg>:: 31 The commit message to be used for the merge commit (in case 32 it is created). The `git-fmt-merge-msg` script can be used 33 to give a good default for automated `git-merge` invocations. 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 40include::merge-strategies.txt[] 41 42 43If you tried a merge which resulted in a complex conflicts and 44would want to start over, you can recover with 45gitlink:git-reset[1]. 46 47CONFIGURATION 48------------- 49 50merge.summary:: 51 Whether to include summaries of merged commits in newly 52 created merge commit. False by default. 53 54merge.verbosity:: 55 Controls the amount of output shown by the recursive merge 56 strategy. Level 0 outputs nothing except a final error 57 message if conflicts were detected. Level 1 outputs only 58 conflicts, 2 outputs conflicts and file changes. Level 5 and 59 above outputs debugging information. The default is level 2. 60 Can be overridden by 'GIT_MERGE_VERBOSITY' environment variable. 61 62 63HOW MERGE WORKS 64--------------- 65 66A merge is always between the current `HEAD` and one or more 67remote branch heads, and the index file must exactly match the 68tree of `HEAD` commit (i.e. the contents of the last commit) when 69it happens. In other words, `git-diff --cached HEAD` must 70report no changes. 71 72[NOTE] 73This is a bit of lie. In certain special cases, your index are 74allowed to be different from the tree of `HEAD` commit. The most 75notable case is when your `HEAD` commit is already ahead of what 76is being merged, in which case your index can have arbitrary 77difference from your `HEAD` commit. Otherwise, your index entries 78are allowed have differences from your `HEAD` commit that match 79the result of trivial merge (e.g. you received the same patch 80from external source to produce the same result as what you are 81merging). For example, if a path did not exist in the common 82ancestor and your head commit but exists in the tree you are 83merging into your repository, and if you already happen to have 84that path exactly in your index, the merge does not have to 85fail. 86 87Otherwise, merge will refuse to do any harm to your repository 88(that is, it may fetch the objects from remote, and it may even 89update the local branch used to keep track of the remote branch 90with `git pull remote rbranch:lbranch`, but your working tree, 91`.git/HEAD` pointer and index file are left intact). 92 93You may have local modifications in the working tree files. In 94other words, `git-diff` is allowed to report changes. 95However, the merge uses your working tree as the working area, 96and in order to prevent the merge operation from losing such 97changes, it makes sure that they do not interfere with the 98merge. Those complex tables in read-tree documentation define 99what it means for a path to "interfere with the merge". And if 100your local modifications interfere with the merge, again, it 101stops before touching anything. 102 103So in the above two "failed merge" case, you do not have to 104worry about loss of data --- you simply were not ready to do 105a merge, so no merge happened at all. You may want to finish 106whatever you were in the middle of doing, and retry the same 107pull after you are done and ready. 108 109When things cleanly merge, these things happen: 110 1111. The results are updated both in the index file and in your 112 working tree; 1132. Index file is written out as a tree; 1143. The tree gets committed; and 1154. The `HEAD` pointer gets advanced. 116 117Because of 2., we require that the original state of the index 118file to match exactly the current `HEAD` commit; otherwise we 119will write out your local changes already registered in your 120index file along with the merge result, which is not good. 121Because 1. involves only the paths different between your 122branch and the remote branch you are pulling from during the 123merge (which is typically a fraction of the whole tree), you can 124have local modifications in your working tree as long as they do 125not overlap with what the merge updates. 126 127When there are conflicts, these things happen: 128 1291. `HEAD` stays the same. 130 1312. Cleanly merged paths are updated both in the index file and 132 in your working tree. 133 1343. For conflicting paths, the index file records up to three 135 versions; stage1 stores the version from the common ancestor, 136 stage2 from `HEAD`, and stage3 from the remote branch (you 137 can inspect the stages with `git-ls-files -u`). The working 138 tree files have the result of "merge" program; i.e. 3-way 139 merge result with familiar conflict markers `<<< === >>>`. 140 1414. No other changes are done. In particular, the local 142 modifications you had before you started merge will stay the 143 same and the index entries for them stay as they were, 144 i.e. matching `HEAD`. 145 146After seeing a conflict, you can do two things: 147 148 * Decide not to merge. The only clean-up you need are to reset 149 the index file to the `HEAD` commit to reverse 2. and to clean 150 up working tree changes made by 2. and 3.; `git-reset` can 151 be used for this. 152 153 * Resolve the conflicts. `git-diff` would report only the 154 conflicting paths because of the above 2. and 3.. Edit the 155 working tree files into a desirable shape, `git-add` or `git-rm` 156 them, to make the index file contain what the merge result 157 should be, and run `git-commit` to commit the result. 158 159 160SEE ALSO 161-------- 162gitlink:git-fmt-merge-msg[1], gitlink:git-pull[1] 163 164 165Author 166------ 167Written by Junio C Hamano <junkio@cox.net> 168 169 170Documentation 171-------------- 172Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. 173 174GIT 175--- 176Part of the gitlink:git[7] suite