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 45linkgit: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 71commits (usually, branch head or tag), and the index file must 72exactly match the 73tree of `HEAD` commit (i.e. the contents of the last commit) when 74it happens. In other words, `git-diff --cached HEAD` must 75report no changes. 76 77[NOTE] 78This is a bit of a lie. In certain special cases, your index is 79allowed to be different from the tree of the `HEAD` commit. The most 80notable case is when your `HEAD` commit is already ahead of what 81is being merged, in which case your index can have arbitrary 82differences from your `HEAD` commit. Also, your index entries 83may have differences from your `HEAD` commit that match 84the result of a trivial merge (e.g. you received the same patch 85from an external source to produce the same result as what you are 86merging). For example, if a path did not exist in the common 87ancestor and your head commit but exists in the tree you are 88merging into your repository, and if you already happen to have 89that path exactly in your index, the merge does not have to 90fail. 91 92Otherwise, merge will refuse to do any harm to your repository 93(that is, it may fetch the objects from remote, and it may even 94update the local branch used to keep track of the remote branch 95with `git pull remote rbranch:lbranch`, but your working tree, 96`.git/HEAD` pointer and index file are left intact). 97 98You may have local modifications in the working tree files. In 99other words, `git-diff` is allowed to report changes. 100However, the merge uses your working tree as the working area, 101and in order to prevent the merge operation from losing such 102changes, it makes sure that they do not interfere with the 103merge. Those complex tables in read-tree documentation define 104what it means for a path to "interfere with the merge". And if 105your local modifications interfere with the merge, again, it 106stops before touching anything. 107 108So in the above two "failed merge" case, you do not have to 109worry about loss of data --- you simply were not ready to do 110a merge, so no merge happened at all. You may want to finish 111whatever you were in the middle of doing, and retry the same 112pull after you are done and ready. 113 114When things cleanly merge, these things happen: 115 1161. The results are updated both in the index file and in your 117 working tree; 1182. Index file is written out as a tree; 1193. The tree gets committed; and 1204. The `HEAD` pointer gets advanced. 121 122Because of 2., we require that the original state of the index 123file to match exactly the current `HEAD` commit; otherwise we 124will write out your local changes already registered in your 125index file along with the merge result, which is not good. 126Because 1. involves only the paths different between your 127branch and the remote branch you are pulling from during the 128merge (which is typically a fraction of the whole tree), you can 129have local modifications in your working tree as long as they do 130not overlap with what the merge updates. 131 132When there are conflicts, these things happen: 133 1341. `HEAD` stays the same. 135 1362. Cleanly merged paths are updated both in the index file and 137 in your working tree. 138 1393. For conflicting paths, the index file records up to three 140 versions; stage1 stores the version from the common ancestor, 141 stage2 from `HEAD`, and stage3 from the remote branch (you 142 can inspect the stages with `git-ls-files -u`). The working 143 tree files have the result of "merge" program; i.e. 3-way 144 merge result with familiar conflict markers `<<< === >>>`. 145 1464. No other changes are done. In particular, the local 147 modifications you had before you started merge will stay the 148 same and the index entries for them stay as they were, 149 i.e. matching `HEAD`. 150 151After seeing a conflict, you can do two things: 152 153 * Decide not to merge. The only clean-up you need are to reset 154 the index file to the `HEAD` commit to reverse 2. and to clean 155 up working tree changes made by 2. and 3.; `git-reset` can 156 be used for this. 157 158 * Resolve the conflicts. `git-diff` would report only the 159 conflicting paths because of the above 2. and 3.. Edit the 160 working tree files into a desirable shape, `git-add` or `git-rm` 161 them, to make the index file contain what the merge result 162 should be, and run `git-commit` to commit the result. 163 164 165SEE ALSO 166-------- 167linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1], 168linkgit:gitattributes[5] 169 170 171Author 172------ 173Written by Junio C Hamano <junkio@cox.net> 174 175 176Documentation 177-------------- 178Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. 179 180GIT 181--- 182Part of the linkgit:git[7] suite