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 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 46CONFIGURATION 47------------- 48 49merge.summary:: 50 Whether to include summaries of merged commits in newly 51 created merge commit. False by default. 52 53merge.verbosity:: 54 Controls the amount of output shown by the recursive merge 55 strategy. Level 0 outputs nothing except a final error 56 message if conflicts were detected. Level 1 outputs only 57 conflicts, 2 outputs conflicts and file changes. Level 5 and 58 above outputs debugging information. The default is level 2. 59 Can be overridden by 'GIT_MERGE_VERBOSITY' environment variable. 60 61branch.<name>.mergeoptions:: 62 Sets default options for merging into branch <name>. The syntax and 63 supported options are equal to that of git-merge, but option values 64 containing whitespace characters are currently not supported. 65 66HOW MERGE WORKS 67--------------- 68 69A merge is always between the current `HEAD` and one or more 70remote branch heads, and the index file must exactly match the 71tree of `HEAD` commit (i.e. the contents of the last commit) when 72it happens. In other words, `git-diff --cached HEAD` must 73report no changes. 74 75[NOTE] 76This is a bit of lie. In certain special cases, your index are 77allowed to be different from the tree of `HEAD` commit. The most 78notable case is when your `HEAD` commit is already ahead of what 79is being merged, in which case your index can have arbitrary 80difference from your `HEAD` commit. Otherwise, your index entries 81are allowed have differences from your `HEAD` commit that match 82the result of trivial merge (e.g. you received the same patch 83from external source to produce the same result as what you are 84merging). For example, if a path did not exist in the common 85ancestor and your head commit but exists in the tree you are 86merging into your repository, and if you already happen to have 87that path exactly in your index, the merge does not have to 88fail. 89 90Otherwise, merge will refuse to do any harm to your repository 91(that is, it may fetch the objects from remote, and it may even 92update the local branch used to keep track of the remote branch 93with `git pull remote rbranch:lbranch`, but your working tree, 94`.git/HEAD` pointer and index file are left intact). 95 96You may have local modifications in the working tree files. In 97other words, `git-diff` is allowed to report changes. 98However, the merge uses your working tree as the working area, 99and in order to prevent the merge operation from losing such 100changes, it makes sure that they do not interfere with the 101merge. Those complex tables in read-tree documentation define 102what it means for a path to "interfere with the merge". And if 103your local modifications interfere with the merge, again, it 104stops before touching anything. 105 106So in the above two "failed merge" case, you do not have to 107worry about loss of data --- you simply were not ready to do 108a merge, so no merge happened at all. You may want to finish 109whatever you were in the middle of doing, and retry the same 110pull after you are done and ready. 111 112When things cleanly merge, these things happen: 113 1141. The results are updated both in the index file and in your 115 working tree; 1162. Index file is written out as a tree; 1173. The tree gets committed; and 1184. The `HEAD` pointer gets advanced. 119 120Because of 2., we require that the original state of the index 121file to match exactly the current `HEAD` commit; otherwise we 122will write out your local changes already registered in your 123index file along with the merge result, which is not good. 124Because 1. involves only the paths different between your 125branch and the remote branch you are pulling from during the 126merge (which is typically a fraction of the whole tree), you can 127have local modifications in your working tree as long as they do 128not overlap with what the merge updates. 129 130When there are conflicts, these things happen: 131 1321. `HEAD` stays the same. 133 1342. Cleanly merged paths are updated both in the index file and 135 in your working tree. 136 1373. For conflicting paths, the index file records up to three 138 versions; stage1 stores the version from the common ancestor, 139 stage2 from `HEAD`, and stage3 from the remote branch (you 140 can inspect the stages with `git-ls-files -u`). The working 141 tree files have the result of "merge" program; i.e. 3-way 142 merge result with familiar conflict markers `<<< === >>>`. 143 1444. No other changes are done. In particular, the local 145 modifications you had before you started merge will stay the 146 same and the index entries for them stay as they were, 147 i.e. matching `HEAD`. 148 149After seeing a conflict, you can do two things: 150 151 * Decide not to merge. The only clean-up you need are to reset 152 the index file to the `HEAD` commit to reverse 2. and to clean 153 up working tree changes made by 2. and 3.; `git-reset` can 154 be used for this. 155 156 * Resolve the conflicts. `git-diff` would report only the 157 conflicting paths because of the above 2. and 3.. Edit the 158 working tree files into a desirable shape, `git-add` or `git-rm` 159 them, to make the index file contain what the merge result 160 should be, and run `git-commit` to commit the result. 161 162 163SEE ALSO 164-------- 165gitlink:git-fmt-merge-msg[1], gitlink:git-pull[1] 166 167 168Author 169------ 170Written by Junio C Hamano <junkio@cox.net> 171 172 173Documentation 174-------------- 175Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. 176 177GIT 178--- 179Part of the gitlink:git[7] suite