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 61 62HOW MERGE WORKS 63--------------- 64 65A merge is always between the current `HEAD` and one or more 66remote branch heads, and the index file must exactly match the 67tree of `HEAD` commit (i.e. the contents of the last commit) when 68it happens. In other words, `git-diff --cached HEAD` must 69report no changes. 70 71[NOTE] 72This is a bit of lie. In certain special cases, your index are 73allowed to be different from the tree of `HEAD` commit. The most 74notable case is when your `HEAD` commit is already ahead of what 75is being merged, in which case your index can have arbitrary 76difference from your `HEAD` commit. Otherwise, your index entries 77are allowed have differences from your `HEAD` commit that match 78the result of trivial merge (e.g. you received the same patch 79from external source to produce the same result as what you are 80merging). For example, if a path did not exist in the common 81ancestor and your head commit but exists in the tree you are 82merging into your repository, and if you already happen to have 83that path exactly in your index, the merge does not have to 84fail. 85 86Otherwise, merge will refuse to do any harm to your repository 87(that is, it may fetch the objects from remote, and it may even 88update the local branch used to keep track of the remote branch 89with `git pull remote rbranch:lbranch`, but your working tree, 90`.git/HEAD` pointer and index file are left intact). 91 92You may have local modifications in the working tree files. In 93other words, `git-diff` is allowed to report changes. 94However, the merge uses your working tree as the working area, 95and in order to prevent the merge operation from losing such 96changes, it makes sure that they do not interfere with the 97merge. Those complex tables in read-tree documentation define 98what it means for a path to "interfere with the merge". And if 99your local modifications interfere with the merge, again, it 100stops before touching anything. 101 102So in the above two "failed merge" case, you do not have to 103worry about loss of data --- you simply were not ready to do 104a merge, so no merge happened at all. You may want to finish 105whatever you were in the middle of doing, and retry the same 106pull after you are done and ready. 107 108When things cleanly merge, these things happen: 109 1101. The results are updated both in the index file and in your 111 working tree; 1122. Index file is written out as a tree; 1133. The tree gets committed; and 1144. The `HEAD` pointer gets advanced. 115 116Because of 2., we require that the original state of the index 117file to match exactly the current `HEAD` commit; otherwise we 118will write out your local changes already registered in your 119index file along with the merge result, which is not good. 120Because 1. involves only the paths different between your 121branch and the remote branch you are pulling from during the 122merge (which is typically a fraction of the whole tree), you can 123have local modifications in your working tree as long as they do 124not overlap with what the merge updates. 125 126When there are conflicts, these things happen: 127 1281. `HEAD` stays the same. 129 1302. Cleanly merged paths are updated both in the index file and 131 in your working tree. 132 1333. For conflicting paths, the index file records up to three 134 versions; stage1 stores the version from the common ancestor, 135 stage2 from `HEAD`, and stage3 from the remote branch (you 136 can inspect the stages with `git-ls-files -u`). The working 137 tree files have the result of "merge" program; i.e. 3-way 138 merge result with familiar conflict markers `<<< === >>>`. 139 1404. No other changes are done. In particular, the local 141 modifications you had before you started merge will stay the 142 same and the index entries for them stay as they were, 143 i.e. matching `HEAD`. 144 145After seeing a conflict, you can do two things: 146 147 * Decide not to merge. The only clean-up you need are to reset 148 the index file to the `HEAD` commit to reverse 2. and to clean 149 up working tree changes made by 2. and 3.; `git-reset` can 150 be used for this. 151 152 * Resolve the conflicts. `git-diff` would report only the 153 conflicting paths because of the above 2. and 3.. Edit the 154 working tree files into a desirable shape, `git-add` or `git-rm` 155 them, to make the index file contain what the merge result 156 should be, and run `git-commit` to commit the result. 157 158 159SEE ALSO 160-------- 161gitlink:git-fmt-merge-msg[1], gitlink:git-pull[1] 162 163 164Author 165------ 166Written by Junio C Hamano <junkio@cox.net> 167 168 169Documentation 170-------------- 171Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. 172 173GIT 174--- 175Part of the gitlink:git[7] suite