Documentation/git-merge.txt

   1 git-merge(1)
   2 ============
   3
   4 NAME
   5 ----
   6 git-merge - Join two or more development histories together
   7
   8
   9 SYNOPSIS
  10 --------
  11 [verse]
  12 'git merge' [-n] [--stat] [--no-commit] [--squash] [-s <strategy>]...
  13         [-m <msg>] <remote>...
  14 'git merge' <msg> HEAD <remote>...
  15
  16 DESCRIPTION
  17 -----------
  18 This is the top-level interface to the merge machinery
  19 which drives multiple merge strategy scripts.
  20
  21 The second syntax (<msg> `HEAD` <remote>) is supported for
  22 historical reasons.  Do not use it from the command line or in
  23 new scripts.  It is the same as `git merge -m <msg> <remote>`.
  24
  25
  26 OPTIONS
  27 -------
  28 include::merge-options.txt[]
  29
  30 -m <msg>::
  31         Set the commit message to be used for the merge commit (in
  32         case one is created). The 'git fmt-merge-msg' command can be
  33         used to give a good default for automated 'git merge'
  34         invocations.
  35
  36 <remote>...::
  37         Other branch heads to merge into our branch.  You need at
  38         least one <remote>.  Specifying more than one <remote>
  39         obviously means you are trying an Octopus.
  40
  41 include::merge-strategies.txt[]
  42
  43
  44 If you tried a merge which resulted in complex conflicts and
  45 want to start over, you can recover with 'git-reset'.
  46
  47 CONFIGURATION
  48 -------------
  49 include::merge-config.txt[]
  50
  51 branch.<name>.mergeoptions::
  52         Sets default options for merging into branch <name>. The syntax and
  53         supported options are the same as those of 'git merge', but option
  54         values containing whitespace characters are currently not supported.
  55
  56 HOW MERGE WORKS
  57 ---------------
  58
  59 A merge is always between the current `HEAD` and one or more
  60 commits (usually, branch head or tag), and the index file must
  61 match the tree of `HEAD` commit (i.e. the contents of the last commit)
  62 when it starts out.  In other words, `git diff --cached HEAD` must
  63 report no changes.  (One exception is when the changed index
  64 entries are already in the same state that would result from
  65 the merge anyway.)
  66
  67 Three kinds of merge can happen:
  68
  69 * The merged commit is already contained in `HEAD`. This is the
  70   simplest case, called "Already up-to-date."
  71
  72 * `HEAD` is already contained in the merged commit. This is the
  73   most common case especially when invoked from 'git pull':
  74   you are tracking an upstream repository, have committed no local
  75   changes and now you want to update to a newer upstream revision.
  76   Your `HEAD` (and the index) is updated to point at the merged
  77   commit, without creating an extra merge commit.  This is
  78   called "Fast-forward".
  79
  80 * Both the merged commit and `HEAD` are independent and must be
  81   tied together by a merge commit that has both of them as its parents.
  82   The rest of this section describes this "True merge" case.
  83
  84 The chosen merge strategy merges the two commits into a single
  85 new source tree.
  86 When things merge cleanly, this is what happens:
  87
  88 1. The results are updated both in the index file and in your
  89    working tree;
  90 2. Index file is written out as a tree;
  91 3. The tree gets committed; and
  92 4. The `HEAD` pointer gets advanced.
  93
  94 Because of 2., we require that the original state of the index
  95 file matches exactly the current `HEAD` commit; otherwise we
  96 will write out your local changes already registered in your
  97 index file along with the merge result, which is not good.
  98 Because 1. involves only those paths differing between your
  99 branch and the remote branch you are pulling from during the
 100 merge (which is typically a fraction of the whole tree), you can
 101 have local modifications in your working tree as long as they do
 102 not overlap with what the merge updates.
 103
 104 When there are conflicts, the following happens:
 105
 106 1. `HEAD` stays the same.
 107
 108 2. Cleanly merged paths are updated both in the index file and
 109    in your working tree.
 110
 111 3. For conflicting paths, the index file records up to three
 112    versions; stage1 stores the version from the common ancestor,
 113    stage2 from `HEAD`, and stage3 from the remote branch (you
 114    can inspect the stages with `git ls-files -u`).  The working
 115    tree files contain the result of the "merge" program; i.e. 3-way
 116    merge results with familiar conflict markers `<<< === >>>`.
 117
 118 4. No other changes are done.  In particular, the local
 119    modifications you had before you started merge will stay the
 120    same and the index entries for them stay as they were,
 121    i.e. matching `HEAD`.
 122
 123 HOW CONFLICTS ARE PRESENTED
 124 ---------------------------
 125
 126 During a merge, the working tree files are updated to reflect the result
 127 of the merge.  Among the changes made to the common ancestor's version,
 128 non-overlapping ones (that is, you changed an area of the file while the
 129 other side left that area intact, or vice versa) are incorporated in the
 130 final result verbatim.  When both sides made changes to the same area,
 131 however, git cannot randomly pick one side over the other, and asks you to
 132 resolve it by leaving what both sides did to that area.
 133
 134 By default, git uses the same style as that is used by "merge" program
 135 from the RCS suite to present such a conflicted hunk, like this:
 136
 137 ------------
 138 Here are lines that are either unchanged from the common
 139 ancestor, or cleanly resolved because only one side changed.
 140 <<<<<<< yours:sample.txt
 141 Conflict resolution is hard;
 142 let's go shopping.
 143 =======
 144 Git makes conflict resolution easy.
 145 >>>>>>> theirs:sample.txt
 146 And here is another line that is cleanly resolved or unmodified.
 147 ------------
 148
 149 The area where a pair of conflicting changes happened is marked with markers
 150 `<<<<<<<`, `=======`, and `>>>>>>>`.  The part before the `=======`
 151 is typically your side, and the part afterwards is typically their side.
 152
 153 The default format does not show what the original said in the conflicting
 154 area.  You cannot tell how many lines are deleted and replaced with
 155 Barbie's remark on your side.  The only thing you can tell is that your
 156 side wants to say it is hard and you'd prefer to go shopping, while the
 157 other side wants to claim it is easy.
 158
 159 An alternative style can be used by setting the "merge.conflictstyle"
 160 configuration variable to "diff3".  In "diff3" style, the above conflict
 161 may look like this:
 162
 163 ------------
 164 Here are lines that are either unchanged from the common
 165 ancestor, or cleanly resolved because only one side changed.
 166 <<<<<<< yours:sample.txt
 167 Conflict resolution is hard;
 168 let's go shopping.
 169 |||||||
 170 Conflict resolution is hard.
 171 =======
 172 Git makes conflict resolution easy.
 173 >>>>>>> theirs:sample.txt
 174 And here is another line that is cleanly resolved or unmodified.
 175 ------------
 176
 177 In addition to the `<<<<<<<`, `=======`, and `>>>>>>>` markers, it uses
 178 another `|||||||` marker that is followed by the original text.  You can
 179 tell that the original just stated a fact, and your side simply gave in to
 180 that statement and gave up, while the other side tried to have a more
 181 positive attitude.  You can sometimes come up with a better resolution by
 182 viewing the original.
 183
 184
 185 HOW TO RESOLVE CONFLICTS
 186 ------------------------
 187
 188 After seeing a conflict, you can do two things:
 189
 190  * Decide not to merge.  The only clean-ups you need are to reset
 191    the index file to the `HEAD` commit to reverse 2. and to clean
 192    up working tree changes made by 2. and 3.; 'git-reset --hard' can
 193    be used for this.
 194
 195  * Resolve the conflicts.  Git will mark the conflicts in
 196    the working tree.  Edit the files into shape and
 197    'git-add' them to the index.  Use 'git-commit' to seal the deal.
 198
 199 You can work through the conflict with a number of tools:
 200
 201  * Use a mergetool.  'git mergetool' to launch a graphical
 202    mergetool which will work you through the merge.
 203
 204  * Look at the diffs.  'git diff' will show a three-way diff,
 205    highlighting changes from both the HEAD and remote versions.
 206
 207  * Look at the diffs on their own. 'git log --merge -p <path>'
 208    will show diffs first for the HEAD version and then the
 209    remote version.
 210
 211  * Look at the originals.  'git show :1:filename' shows the
 212    common ancestor, 'git show :2:filename' shows the HEAD
 213    version and 'git show :3:filename' shows the remote version.
 214
 215
 216 EXAMPLES
 217 --------
 218
 219 * Merge branches `fixes` and `enhancements` on top of
 220   the current branch, making an octopus merge:
 221 +
 222 ------------------------------------------------
 223 $ git merge fixes enhancements
 224 ------------------------------------------------
 225
 226 * Merge branch `obsolete` into the current branch, using `ours`
 227   merge strategy:
 228 +
 229 ------------------------------------------------
 230 $ git merge -s ours obsolete
 231 ------------------------------------------------
 232
 233 * Merge branch `maint` into the current branch, but do not make
 234   a new commit automatically:
 235 +
 236 ------------------------------------------------
 237 $ git merge --no-commit maint
 238 ------------------------------------------------
 239 +
 240 This can be used when you want to include further changes to the
 241 merge, or want to write your own merge commit message.
 242 +
 243 You should refrain from abusing this option to sneak substantial
 244 changes into a merge commit.  Small fixups like bumping
 245 release/version name would be acceptable.
 246
 247
 248 SEE ALSO
 249 --------
 250 linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],
 251 linkgit:gitattributes[5],
 252 linkgit:git-reset[1],
 253 linkgit:git-diff[1], linkgit:git-ls-files[1],
 254 linkgit:git-add[1], linkgit:git-rm[1],
 255 linkgit:git-mergetool[1]
 256
 257 Author
 258 ------
 259 Written by Junio C Hamano <gitster@pobox.com>
 260
 261
 262 Documentation
 263 --------------
 264 Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
 265
 266 GIT
 267 ---
 268 Part of the linkgit:git[1] suite