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 heads to merge 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 complex conflicts and 44want 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 60match the tree of `HEAD` commit (i.e. the contents of the last commit) 61when it starts out. In other words, `git diff --cached HEAD` must 62report no changes. (One exception is when the changed index 63entries are already in the same state that would result from 64the merge anyway.) 65 66Three kinds of merge can happen: 67 68* The merged commit is already contained in `HEAD`. This is the 69 simplest case, called "Already up-to-date." 70 71* `HEAD` is already contained in the merged commit. This is the 72 most common case especially when invoked from 'git pull': 73 you are tracking an upstream repository, have committed no local 74 changes and now you want to update to a newer upstream revision. 75 Your `HEAD` (and the index) is updated to point at the merged 76 commit, without creating an extra merge commit. This is 77 called "Fast-forward". 78 79* Both the merged commit and `HEAD` are independent and must be 80 tied together by a merge commit that has both of them as its parents. 81 The rest of this section describes this "True merge" case. 82 83The chosen merge strategy merges the two commits into a single 84new source tree. 85When things merge cleanly, this is what happens: 86 871. The results are updated both in the index file and in your 88 working tree; 892. Index file is written out as a tree; 903. The tree gets committed; and 914. The `HEAD` pointer gets advanced. 92 93Because of 2., we require that the original state of the index 94file matches exactly the current `HEAD` commit; otherwise we 95will write out your local changes already registered in your 96index file along with the merge result, which is not good. 97Because 1. involves only those paths differing between your 98branch and the remote branch you are pulling from during the 99merge (which is typically a fraction of the whole tree), you can 100have local modifications in your working tree as long as they do 101not overlap with what the merge updates. 102 103When there are conflicts, the following happens: 104 1051. `HEAD` stays the same. 106 1072. Cleanly merged paths are updated both in the index file and 108 in your working tree. 109 1103. For conflicting paths, the index file records up to three 111 versions; stage1 stores the version from the common ancestor, 112 stage2 from `HEAD`, and stage3 from the remote branch (you 113 can inspect the stages with `git ls-files -u`). The working 114 tree files contain the result of the "merge" program; i.e. 3-way 115 merge results with familiar conflict markers `<<< === >>>`. 116 1174. No other changes are done. In particular, the local 118 modifications you had before you started merge will stay the 119 same and the index entries for them stay as they were, 120 i.e. matching `HEAD`. 121 122HOW CONFLICTS ARE PRESENTED 123--------------------------- 124 125During a merge, the working tree files are updated to reflect the result 126of the merge. Among the changes made to the common ancestor's version, 127non-overlapping ones (that is, you changed an area of the file while the 128other side left that area intact, or vice versa) are incorporated in the 129final result verbatim. When both sides made changes to the same area, 130however, git cannot randomly pick one side over the other, and asks you to 131resolve it by leaving what both sides did to that area. 132 133By default, git uses the same style as that is used by "merge" program 134from the RCS suite to present such a conflicted hunk, like this: 135 136------------ 137Here are lines that are either unchanged from the common 138ancestor, or cleanly resolved because only one side changed. 139<<<<<<< yours:sample.txt 140Conflict resolution is hard; 141let's go shopping. 142======= 143Git makes conflict resolution easy. 144>>>>>>> theirs:sample.txt 145And here is another line that is cleanly resolved or unmodified. 146------------ 147 148The area where a pair of conflicting changes happened is marked with markers 149`<<<<<<<`, `=======`, and `>>>>>>>`. The part before the `=======` 150is typically your side, and the part afterwards is typically their side. 151 152The default format does not show what the original said in the conflicting 153area. You cannot tell how many lines are deleted and replaced with 154Barbie's remark on your side. The only thing you can tell is that your 155side wants to say it is hard and you'd prefer to go shopping, while the 156other side wants to claim it is easy. 157 158An alternative style can be used by setting the "merge.conflictstyle" 159configuration variable to "diff3". In "diff3" style, the above conflict 160may look like this: 161 162------------ 163Here are lines that are either unchanged from the common 164ancestor, or cleanly resolved because only one side changed. 165<<<<<<< yours:sample.txt 166Conflict resolution is hard; 167let's go shopping. 168||||||| 169Conflict resolution is hard. 170======= 171Git makes conflict resolution easy. 172>>>>>>> theirs:sample.txt 173And here is another line that is cleanly resolved or unmodified. 174------------ 175 176In addition to the `<<<<<<<`, `=======`, and `>>>>>>>` markers, it uses 177another `|||||||` marker that is followed by the original text. You can 178tell that the original just stated a fact, and your side simply gave in to 179that statement and gave up, while the other side tried to have a more 180positive attitude. You can sometimes come up with a better resolution by 181viewing the original. 182 183 184HOW TO RESOLVE CONFLICTS 185------------------------ 186 187After seeing a conflict, you can do two things: 188 189 * Decide not to merge. The only clean-ups you need are to reset 190 the index file to the `HEAD` commit to reverse 2. and to clean 191 up working tree changes made by 2. and 3.; 'git-reset --hard' can 192 be used for this. 193 194 * Resolve the conflicts. Git will mark the conflicts in 195 the working tree. Edit the files into shape and 196 'git-add' them to the index. Use 'git-commit' to seal the deal. 197 198You can work through the conflict with a number of tools: 199 200 * Use a mergetool. 'git mergetool' to launch a graphical 201 mergetool which will work you through the merge. 202 203 * Look at the diffs. 'git diff' will show a three-way diff, 204 highlighting changes from both the HEAD and remote versions. 205 206 * Look at the diffs on their own. 'git log --merge -p <path>' 207 will show diffs first for the HEAD version and then the 208 remote version. 209 210 * Look at the originals. 'git show :1:filename' shows the 211 common ancestor, 'git show :2:filename' shows the HEAD 212 version and 'git show :3:filename' shows the remote version. 213 214SEE ALSO 215-------- 216linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1], 217linkgit:gitattributes[5], 218linkgit:git-reset[1], 219linkgit:git-diff[1], linkgit:git-ls-files[1], 220linkgit:git-add[1], linkgit:git-rm[1], 221linkgit:git-mergetool[1] 222 223Author 224------ 225Written by Junio C Hamano <gitster@pobox.com> 226 227 228Documentation 229-------------- 230Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. 231 232GIT 233--- 234Part of the linkgit:git[1] suite