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 62branch.<name>.mergeoptions:: 63 Sets default options for merging into branch <name>. The syntax and 64 supported options are equal to that of git-merge, but option values 65 containing whitespace characters are currently not supported. 66 67HOW MERGE WORKS 68--------------- 69 70A merge is always between the current `HEAD` and one or more 71remote branch heads, and the index file must exactly match the 72tree of `HEAD` commit (i.e. the contents of the last commit) when 73it happens. In other words, `git-diff --cached HEAD` must 74report no changes. 75 76[NOTE] 77This is a bit of lie. In certain special cases, your index are 78allowed to be different from the tree of `HEAD` commit. The most 79notable case is when your `HEAD` commit is already ahead of what 80is being merged, in which case your index can have arbitrary 81difference from your `HEAD` commit. Otherwise, your index entries 82are allowed have differences from your `HEAD` commit that match 83the result of trivial merge (e.g. you received the same patch 84from external source to produce the same result as what you are 85merging). For example, if a path did not exist in the common 86ancestor and your head commit but exists in the tree you are 87merging into your repository, and if you already happen to have 88that path exactly in your index, the merge does not have to 89fail. 90 91Otherwise, merge will refuse to do any harm to your repository 92(that is, it may fetch the objects from remote, and it may even 93update the local branch used to keep track of the remote branch 94with `git pull remote rbranch:lbranch`, but your working tree, 95`.git/HEAD` pointer and index file are left intact). 96 97You may have local modifications in the working tree files. In 98other words, `git-diff` is allowed to report changes. 99However, the merge uses your working tree as the working area, 100and in order to prevent the merge operation from losing such 101changes, it makes sure that they do not interfere with the 102merge. Those complex tables in read-tree documentation define 103what it means for a path to "interfere with the merge". And if 104your local modifications interfere with the merge, again, it 105stops before touching anything. 106 107So in the above two "failed merge" case, you do not have to 108worry about loss of data --- you simply were not ready to do 109a merge, so no merge happened at all. You may want to finish 110whatever you were in the middle of doing, and retry the same 111pull after you are done and ready. 112 113When things cleanly merge, these things happen: 114 1151. The results are updated both in the index file and in your 116 working tree; 1172. Index file is written out as a tree; 1183. The tree gets committed; and 1194. The `HEAD` pointer gets advanced. 120 121Because of 2., we require that the original state of the index 122file to match exactly the current `HEAD` commit; otherwise we 123will write out your local changes already registered in your 124index file along with the merge result, which is not good. 125Because 1. involves only the paths different between your 126branch and the remote branch you are pulling from during the 127merge (which is typically a fraction of the whole tree), you can 128have local modifications in your working tree as long as they do 129not overlap with what the merge updates. 130 131When there are conflicts, these things happen: 132 1331. `HEAD` stays the same. 134 1352. Cleanly merged paths are updated both in the index file and 136 in your working tree. 137 1383. For conflicting paths, the index file records up to three 139 versions; stage1 stores the version from the common ancestor, 140 stage2 from `HEAD`, and stage3 from the remote branch (you 141 can inspect the stages with `git-ls-files -u`). The working 142 tree files have the result of "merge" program; i.e. 3-way 143 merge result with familiar conflict markers `<<< === >>>`. 144 1454. No other changes are done. In particular, the local 146 modifications you had before you started merge will stay the 147 same and the index entries for them stay as they were, 148 i.e. matching `HEAD`. 149 150After seeing a conflict, you can do two things: 151 152 * Decide not to merge. The only clean-up you need are to reset 153 the index file to the `HEAD` commit to reverse 2. and to clean 154 up working tree changes made by 2. and 3.; `git-reset` can 155 be used for this. 156 157 * Resolve the conflicts. `git-diff` would report only the 158 conflicting paths because of the above 2. and 3.. Edit the 159 working tree files into a desirable shape, `git-add` or `git-rm` 160 them, to make the index file contain what the merge result 161 should be, and run `git-commit` to commit the result. 162 163 164SEE ALSO 165-------- 166gitlink:git-fmt-merge-msg[1], gitlink:git-pull[1] 167 168 169Author 170------ 171Written by Junio C Hamano <junkio@cox.net> 172 173 174Documentation 175-------------- 176Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. 177 178GIT 179--- 180Part of the gitlink:git[7] suite