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] [--stat] [--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 'git-reset'. 45 46CONFIGURATION 47------------- 48include::merge-config.txt[] 49 50branch.<name>.mergeoptions:: 51 Sets default options for merging into branch <name>. The syntax and 52 supported options are equal to that of 'git-merge', but option values 53 containing whitespace characters are currently not supported. 54 55HOW MERGE WORKS 56--------------- 57 58A merge is always between the current `HEAD` and one or more 59commits (usually, branch head or tag), and the index file must 60exactly match the 61tree of `HEAD` commit (i.e. the contents of the last commit) when 62it happens. In other words, `git diff --cached HEAD` must 63report no changes. 64 65[NOTE] 66This is a bit of a lie. In certain special cases, your index is 67allowed to be different from the tree of the `HEAD` commit. The most 68notable case is when your `HEAD` commit is already ahead of what 69is being merged, in which case your index can have arbitrary 70differences from your `HEAD` commit. Also, your index entries 71may have differences from your `HEAD` commit that match 72the result of a trivial merge (e.g. you received the same patch 73from an external source to produce the same result as what you are 74merging). For example, if a path did not exist in the common 75ancestor and your head commit but exists in the tree you are 76merging into your repository, and if you already happen to have 77that path exactly in your index, the merge does not have to 78fail. 79 80Otherwise, merge will refuse to do any harm to your repository 81(that is, it may fetch the objects from remote, and it may even 82update the local branch used to keep track of the remote branch 83with `git pull remote rbranch:lbranch`, but your working tree, 84`.git/HEAD` pointer and index file are left intact). 85 86You may have local modifications in the working tree files. In 87other words, 'git-diff' is allowed to report changes. 88However, the merge uses your working tree as the working area, 89and in order to prevent the merge operation from losing such 90changes, it makes sure that they do not interfere with the 91merge. Those complex tables in read-tree documentation define 92what it means for a path to "interfere with the merge". And if 93your local modifications interfere with the merge, again, it 94stops before touching anything. 95 96So in the above two "failed merge" case, you do not have to 97worry about loss of data --- you simply were not ready to do 98a merge, so no merge happened at all. You may want to finish 99whatever you were in the middle of doing, and retry the same 100pull after you are done and ready. 101 102When things cleanly merge, these things happen: 103 1041. The results are updated both in the index file and in your 105 working tree; 1062. Index file is written out as a tree; 1073. The tree gets committed; and 1084. The `HEAD` pointer gets advanced. 109 110Because of 2., we require that the original state of the index 111file to match exactly the current `HEAD` commit; otherwise we 112will write out your local changes already registered in your 113index file along with the merge result, which is not good. 114Because 1. involves only the paths different between your 115branch and the remote branch you are pulling from during the 116merge (which is typically a fraction of the whole tree), you can 117have local modifications in your working tree as long as they do 118not overlap with what the merge updates. 119 120When there are conflicts, these things happen: 121 1221. `HEAD` stays the same. 123 1242. Cleanly merged paths are updated both in the index file and 125 in your working tree. 126 1273. For conflicting paths, the index file records up to three 128 versions; stage1 stores the version from the common ancestor, 129 stage2 from `HEAD`, and stage3 from the remote branch (you 130 can inspect the stages with `git ls-files -u`). The working 131 tree files have the result of "merge" program; i.e. 3-way 132 merge result with familiar conflict markers `<<< === >>>`. 133 1344. No other changes are done. In particular, the local 135 modifications you had before you started merge will stay the 136 same and the index entries for them stay as they were, 137 i.e. matching `HEAD`. 138 139After seeing a conflict, you can do two things: 140 141 * Decide not to merge. The only clean-up you need are to reset 142 the index file to the `HEAD` commit to reverse 2. and to clean 143 up working tree changes made by 2. and 3.; 'git-reset' can 144 be used for this. 145 146 * Resolve the conflicts. `git diff` would report only the 147 conflicting paths because of the above 2. and 3. Edit the 148 working tree files into a desirable shape, 'git-add' or 'git-rm' 149 them, to make the index file contain what the merge result 150 should be, and run 'git-commit' to commit the result. 151 152 153SEE ALSO 154-------- 155linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1], 156linkgit:gitattributes[5], 157linkgit:git-reset[1], 158linkgit:git-diff[1], linkgit:git-ls-files[1], 159linkgit:git-add[1], linkgit:git-rm[1], 160linkgit:git-mergetool[1] 161 162Author 163------ 164Written by Junio C Hamano <junkio@cox.net> 165 166 167Documentation 168-------------- 169Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. 170 171GIT 172--- 173Part of the linkgit:git[1] suite