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]
  13         [-s <strategy>] [-X <strategy-option>]
  14         [--[no-]rerere-autoupdate] [-m <msg>] <commit>...
  15 'git merge' <msg> HEAD <commit>...
  16
  17 DESCRIPTION
  18 -----------
  19 Incorporates changes from the named commits (since the time their
  20 histories diverged from the current branch) into the current
  21 branch.  This command is used by 'git pull' to incorporate changes
  22 from another repository and can be used by hand to merge changes
  23 from one branch into another.
  24
  25 Assume the following history exists and the current branch is
  26 "`master`":
  27
  28 ------------
  29           A---B---C topic
  30          /
  31     D---E---F---G master
  32 ------------
  33
  34 Then "`git merge topic`" will replay the changes made on the
  35 `topic` branch since it diverged from `master` (i.e., `E`) until
  36 its current commit (`C`) on top of `master`, and record the result
  37 in a new commit along with the names of the two parent commits and
  38 a log message from the user describing the changes.
  39
  40 ------------
  41           A---B---C topic
  42          /         \
  43     D---E---F---G---H master
  44 ------------
  45
  46 The second syntax (<msg> `HEAD` <commit>...) is supported for
  47 historical reasons.  Do not use it from the command line or in
  48 new scripts.  It is the same as `git merge -m <msg> <commit>...`.
  49
  50 *Warning*: Running 'git merge' with uncommitted changes is
  51 discouraged: while possible, it leaves you in a state that is hard to
  52 back out of in the case of a conflict.
  53
  54
  55 OPTIONS
  56 -------
  57 include::merge-options.txt[]
  58
  59 -m <msg>::
  60         Set the commit message to be used for the merge commit (in
  61         case one is created).
  62 +
  63 If `--log` is specified, a shortlog of the commits being merged
  64 will be appended to the specified message.
  65 +
  66 The 'git fmt-merge-msg' command can be
  67 used to give a good default for automated 'git merge'
  68 invocations.
  69
  70 --rerere-autoupdate::
  71 --no-rerere-autoupdate::
  72         Allow the rerere mechanism to update the index with the
  73         result of auto-conflict resolution if possible.
  74
  75 <commit>...::
  76         Commits, usually other branch heads, to merge into our branch.
  77         You need at least one <commit>.  Specifying more than one
  78         <commit> obviously means you are trying an Octopus.
  79
  80
  81 PRE-MERGE CHECKS
  82 ----------------
  83
  84 Before applying outside changes, you should get your own work in
  85 good shape and committed locally, so it will not be clobbered if
  86 there are conflicts.  See also linkgit:git-stash[1].
  87 'git pull' and 'git merge' will stop without doing anything when
  88 local uncommitted changes overlap with files that 'git pull'/'git
  89 merge' may need to update.
  90
  91 To avoid recording unrelated changes in the merge commit,
  92 'git pull' and 'git merge' will also abort if there are any changes
  93 registered in the index relative to the `HEAD` commit.  (One
  94 exception is when the changed index entries are in the state that
  95 would result from the merge already.)
  96
  97 If all named commits are already ancestors of `HEAD`, 'git merge'
  98 will exit early with the message "Already up-to-date."
  99
 100 FAST-FORWARD MERGE
 101 ------------------
 102
 103 Often the current branch head is an ancestor of the named commit.
 104 This is the most common case especially when invoked from 'git
 105 pull': you are tracking an upstream repository, you have committed
 106 no local changes, and now you want to update to a newer upstream
 107 revision.  In this case, a new commit is not needed to store the
 108 combined history; instead, the `HEAD` (along with the index) is
 109 updated to point at the named commit, without creating an extra
 110 merge commit.
 111
 112 This behavior can be suppressed with the `--no-ff` option.
 113
 114 TRUE MERGE
 115 ----------
 116
 117 Except in a fast-forward merge (see above), the branches to be
 118 merged must be tied together by a merge commit that has both of them
 119 as its parents.
 120
 121 A merged version reconciling the changes from all branches to be
 122 merged is committed, and your `HEAD`, index, and working tree are
 123 updated to it.  It is possible to have modifications in the working
 124 tree as long as they do not overlap; the update will preserve them.
 125
 126 When it is not obvious how to reconcile the changes, the following
 127 happens:
 128
 129 1. The `HEAD` pointer stays the same.
 130 2. The `MERGE_HEAD` ref is set to point to the other branch head.
 131 3. Paths that merged cleanly are updated both in the index file and
 132    in your working tree.
 133 4. For conflicting paths, the index file records up to three
 134    versions: stage 1 stores the version from the common ancestor,
 135    stage 2 from `HEAD`, and stage 3 from `MERGE_HEAD` (you
 136    can inspect the stages with `git ls-files -u`).  The working
 137    tree files contain the result of the "merge" program; i.e. 3-way
 138    merge results with familiar conflict markers `<<<` `===` `>>>`.
 139 5. No other changes are made.  In particular, the local
 140    modifications you had before you started merge will stay the
 141    same and the index entries for them stay as they were,
 142    i.e. matching `HEAD`.
 143
 144 If you tried a merge which resulted in complex conflicts and
 145 want to start over, you can recover with `git reset --merge`.
 146
 147 HOW CONFLICTS ARE PRESENTED
 148 ---------------------------
 149
 150 During a merge, the working tree files are updated to reflect the result
 151 of the merge.  Among the changes made to the common ancestor's version,
 152 non-overlapping ones (that is, you changed an area of the file while the
 153 other side left that area intact, or vice versa) are incorporated in the
 154 final result verbatim.  When both sides made changes to the same area,
 155 however, git cannot randomly pick one side over the other, and asks you to
 156 resolve it by leaving what both sides did to that area.
 157
 158 By default, git uses the same style as that is used by "merge" program
 159 from the RCS suite to present such a conflicted hunk, like this:
 160
 161 ------------
 162 Here are lines that are either unchanged from the common
 163 ancestor, or cleanly resolved because only one side changed.
 164 <<<<<<< yours:sample.txt
 165 Conflict resolution is hard;
 166 let's go shopping.
 167 =======
 168 Git makes conflict resolution easy.
 169 >>>>>>> theirs:sample.txt
 170 And here is another line that is cleanly resolved or unmodified.
 171 ------------
 172
 173 The area where a pair of conflicting changes happened is marked with markers
 174 `<<<<<<<`, `=======`, and `>>>>>>>`.  The part before the `=======`
 175 is typically your side, and the part afterwards is typically their side.
 176
 177 The default format does not show what the original said in the conflicting
 178 area.  You cannot tell how many lines are deleted and replaced with
 179 Barbie's remark on your side.  The only thing you can tell is that your
 180 side wants to say it is hard and you'd prefer to go shopping, while the
 181 other side wants to claim it is easy.
 182
 183 An alternative style can be used by setting the "merge.conflictstyle"
 184 configuration variable to "diff3".  In "diff3" style, the above conflict
 185 may look like this:
 186
 187 ------------
 188 Here are lines that are either unchanged from the common
 189 ancestor, or cleanly resolved because only one side changed.
 190 <<<<<<< yours:sample.txt
 191 Conflict resolution is hard;
 192 let's go shopping.
 193 |||||||
 194 Conflict resolution is hard.
 195 =======
 196 Git makes conflict resolution easy.
 197 >>>>>>> theirs:sample.txt
 198 And here is another line that is cleanly resolved or unmodified.
 199 ------------
 200
 201 In addition to the `<<<<<<<`, `=======`, and `>>>>>>>` markers, it uses
 202 another `|||||||` marker that is followed by the original text.  You can
 203 tell that the original just stated a fact, and your side simply gave in to
 204 that statement and gave up, while the other side tried to have a more
 205 positive attitude.  You can sometimes come up with a better resolution by
 206 viewing the original.
 207
 208
 209 HOW TO RESOLVE CONFLICTS
 210 ------------------------
 211
 212 After seeing a conflict, you can do two things:
 213
 214  * Decide not to merge.  The only clean-ups you need are to reset
 215    the index file to the `HEAD` commit to reverse 2. and to clean
 216    up working tree changes made by 2. and 3.; `git-reset --hard` can
 217    be used for this.
 218
 219  * Resolve the conflicts.  Git will mark the conflicts in
 220    the working tree.  Edit the files into shape and
 221    'git add' them to the index.  Use 'git commit' to seal the deal.
 222
 223 You can work through the conflict with a number of tools:
 224
 225  * Use a mergetool.  `git mergetool` to launch a graphical
 226    mergetool which will work you through the merge.
 227
 228  * Look at the diffs.  `git diff` will show a three-way diff,
 229    highlighting changes from both the `HEAD` and `MERGE_HEAD`
 230    versions.
 231
 232  * Look at the diffs from each branch. `git log --merge -p <path>`
 233    will show diffs first for the `HEAD` version and then the
 234    `MERGE_HEAD` version.
 235
 236  * Look at the originals.  `git show :1:filename` shows the
 237    common ancestor, `git show :2:filename` shows the `HEAD`
 238    version, and `git show :3:filename` shows the `MERGE_HEAD`
 239    version.
 240
 241
 242 EXAMPLES
 243 --------
 244
 245 * Merge branches `fixes` and `enhancements` on top of
 246   the current branch, making an octopus merge:
 247 +
 248 ------------------------------------------------
 249 $ git merge fixes enhancements
 250 ------------------------------------------------
 251
 252 * Merge branch `obsolete` into the current branch, using `ours`
 253   merge strategy:
 254 +
 255 ------------------------------------------------
 256 $ git merge -s ours obsolete
 257 ------------------------------------------------
 258
 259 * Merge branch `maint` into the current branch, but do not make
 260   a new commit automatically:
 261 +
 262 ------------------------------------------------
 263 $ git merge --no-commit maint
 264 ------------------------------------------------
 265 +
 266 This can be used when you want to include further changes to the
 267 merge, or want to write your own merge commit message.
 268 +
 269 You should refrain from abusing this option to sneak substantial
 270 changes into a merge commit.  Small fixups like bumping
 271 release/version name would be acceptable.
 272
 273
 274 include::merge-strategies.txt[]
 275
 276 CONFIGURATION
 277 -------------
 278 include::merge-config.txt[]
 279
 280 branch.<name>.mergeoptions::
 281         Sets default options for merging into branch <name>. The syntax and
 282         supported options are the same as those of 'git merge', but option
 283         values containing whitespace characters are currently not supported.
 284
 285 SEE ALSO
 286 --------
 287 linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],
 288 linkgit:gitattributes[5],
 289 linkgit:git-reset[1],
 290 linkgit:git-diff[1], linkgit:git-ls-files[1],
 291 linkgit:git-add[1], linkgit:git-rm[1],
 292 linkgit:git-mergetool[1]
 293
 294 Author
 295 ------
 296 Written by Junio C Hamano <gitster@pobox.com>
 297
 298
 299 Documentation
 300 --------------
 301 Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
 302
 303 GIT
 304 ---
 305 Part of the linkgit:git[1] suite