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 'git merge' --abort
  17
  18 DESCRIPTION
  19 -----------
  20 Incorporates changes from the named commits (since the time their
  21 histories diverged from the current branch) into the current
  22 branch.  This command is used by 'git pull' to incorporate changes
  23 from another repository and can be used by hand to merge changes
  24 from one branch into another.
  25
  26 Assume the following history exists and the current branch is
  27 "`master`":
  28
  29 ------------
  30           A---B---C topic
  31          /
  32     D---E---F---G master
  33 ------------
  34
  35 Then "`git merge topic`" will replay the changes made on the
  36 `topic` branch since it diverged from `master` (i.e., `E`) until
  37 its current commit (`C`) on top of `master`, and record the result
  38 in a new commit along with the names of the two parent commits and
  39 a log message from the user describing the changes.
  40
  41 ------------
  42           A---B---C topic
  43          /         \
  44     D---E---F---G---H master
  45 ------------
  46
  47 The second syntax (<msg> `HEAD` <commit>...) is supported for
  48 historical reasons.  Do not use it from the command line or in
  49 new scripts.  It is the same as `git merge -m <msg> <commit>...`.
  50
  51 The third syntax ("`git merge --abort`") can only be run after the
  52 merge has resulted in conflicts. 'git merge --abort' will abort the
  53 merge process and try to reconstruct the pre-merge state. However,
  54 if there were uncommitted changes when the merge started (and
  55 especially if those changes were further modified after the merge
  56 was started), 'git merge --abort' will in some cases be unable to
  57 reconstruct the original (pre-merge) changes. Therefore:
  58
  59 *Warning*: Running 'git merge' with uncommitted changes is
  60 discouraged: while possible, it leaves you in a state that is hard to
  61 back out of in the case of a conflict.
  62
  63
  64 OPTIONS
  65 -------
  66 include::merge-options.txt[]
  67
  68 -m <msg>::
  69         Set the commit message to be used for the merge commit (in
  70         case one is created).
  71 +
  72 If `--log` is specified, a shortlog of the commits being merged
  73 will be appended to the specified message.
  74 +
  75 The 'git fmt-merge-msg' command can be
  76 used to give a good default for automated 'git merge'
  77 invocations.
  78
  79 --rerere-autoupdate::
  80 --no-rerere-autoupdate::
  81         Allow the rerere mechanism to update the index with the
  82         result of auto-conflict resolution if possible.
  83
  84 --abort::
  85         Abort the current conflict resolution process, and
  86         try to reconstruct the pre-merge state.
  87 +
  88 If there were uncommitted worktree changes present when the merge
  89 started, 'git merge --abort' will in some cases be unable to
  90 reconstruct these changes. It is therefore recommended to always
  91 commit or stash your changes before running 'git merge'.
  92 +
  93 'git merge --abort' is equivalent to 'git reset --merge' when
  94 `MERGE_HEAD` is present.
  95
  96 <commit>...::
  97         Commits, usually other branch heads, to merge into our branch.
  98         Specifying more than one commit will create a merge with
  99         more than two parents (affectionately called an Octopus merge).
 100 +
 101 If no commit is given from the command line, and if `merge.defaultToUpstream`
 102 configuration variable is set, merge the remote tracking branches
 103 that the current branch is configured to use as its upstream.
 104 See also the configuration section of this manual page.
 105
 106
 107 PRE-MERGE CHECKS
 108 ----------------
 109
 110 Before applying outside changes, you should get your own work in
 111 good shape and committed locally, so it will not be clobbered if
 112 there are conflicts.  See also linkgit:git-stash[1].
 113 'git pull' and 'git merge' will stop without doing anything when
 114 local uncommitted changes overlap with files that 'git pull'/'git
 115 merge' may need to update.
 116
 117 To avoid recording unrelated changes in the merge commit,
 118 'git pull' and 'git merge' will also abort if there are any changes
 119 registered in the index relative to the `HEAD` commit.  (One
 120 exception is when the changed index entries are in the state that
 121 would result from the merge already.)
 122
 123 If all named commits are already ancestors of `HEAD`, 'git merge'
 124 will exit early with the message "Already up-to-date."
 125
 126 FAST-FORWARD MERGE
 127 ------------------
 128
 129 Often the current branch head is an ancestor of the named commit.
 130 This is the most common case especially when invoked from 'git
 131 pull': you are tracking an upstream repository, you have committed
 132 no local changes, and now you want to update to a newer upstream
 133 revision.  In this case, a new commit is not needed to store the
 134 combined history; instead, the `HEAD` (along with the index) is
 135 updated to point at the named commit, without creating an extra
 136 merge commit.
 137
 138 This behavior can be suppressed with the `--no-ff` option.
 139
 140 TRUE MERGE
 141 ----------
 142
 143 Except in a fast-forward merge (see above), the branches to be
 144 merged must be tied together by a merge commit that has both of them
 145 as its parents.
 146
 147 A merged version reconciling the changes from all branches to be
 148 merged is committed, and your `HEAD`, index, and working tree are
 149 updated to it.  It is possible to have modifications in the working
 150 tree as long as they do not overlap; the update will preserve them.
 151
 152 When it is not obvious how to reconcile the changes, the following
 153 happens:
 154
 155 1. The `HEAD` pointer stays the same.
 156 2. The `MERGE_HEAD` ref is set to point to the other branch head.
 157 3. Paths that merged cleanly are updated both in the index file and
 158    in your working tree.
 159 4. For conflicting paths, the index file records up to three
 160    versions: stage 1 stores the version from the common ancestor,
 161    stage 2 from `HEAD`, and stage 3 from `MERGE_HEAD` (you
 162    can inspect the stages with `git ls-files -u`).  The working
 163    tree files contain the result of the "merge" program; i.e. 3-way
 164    merge results with familiar conflict markers `<<<` `===` `>>>`.
 165 5. No other changes are made.  In particular, the local
 166    modifications you had before you started merge will stay the
 167    same and the index entries for them stay as they were,
 168    i.e. matching `HEAD`.
 169
 170 If you tried a merge which resulted in complex conflicts and
 171 want to start over, you can recover with `git merge --abort`.
 172
 173 HOW CONFLICTS ARE PRESENTED
 174 ---------------------------
 175
 176 During a merge, the working tree files are updated to reflect the result
 177 of the merge.  Among the changes made to the common ancestor's version,
 178 non-overlapping ones (that is, you changed an area of the file while the
 179 other side left that area intact, or vice versa) are incorporated in the
 180 final result verbatim.  When both sides made changes to the same area,
 181 however, git cannot randomly pick one side over the other, and asks you to
 182 resolve it by leaving what both sides did to that area.
 183
 184 By default, git uses the same style as that is used by "merge" program
 185 from the RCS suite to present such a conflicted hunk, 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 Git makes conflict resolution easy.
 195 >>>>>>> theirs:sample.txt
 196 And here is another line that is cleanly resolved or unmodified.
 197 ------------
 198
 199 The area where a pair of conflicting changes happened is marked with markers
 200 `<<<<<<<`, `=======`, and `>>>>>>>`.  The part before the `=======`
 201 is typically your side, and the part afterwards is typically their side.
 202
 203 The default format does not show what the original said in the conflicting
 204 area.  You cannot tell how many lines are deleted and replaced with
 205 Barbie's remark on your side.  The only thing you can tell is that your
 206 side wants to say it is hard and you'd prefer to go shopping, while the
 207 other side wants to claim it is easy.
 208
 209 An alternative style can be used by setting the "merge.conflictstyle"
 210 configuration variable to "diff3".  In "diff3" style, the above conflict
 211 may look like this:
 212
 213 ------------
 214 Here are lines that are either unchanged from the common
 215 ancestor, or cleanly resolved because only one side changed.
 216 <<<<<<< yours:sample.txt
 217 Conflict resolution is hard;
 218 let's go shopping.
 219 |||||||
 220 Conflict resolution is hard.
 221 =======
 222 Git makes conflict resolution easy.
 223 >>>>>>> theirs:sample.txt
 224 And here is another line that is cleanly resolved or unmodified.
 225 ------------
 226
 227 In addition to the `<<<<<<<`, `=======`, and `>>>>>>>` markers, it uses
 228 another `|||||||` marker that is followed by the original text.  You can
 229 tell that the original just stated a fact, and your side simply gave in to
 230 that statement and gave up, while the other side tried to have a more
 231 positive attitude.  You can sometimes come up with a better resolution by
 232 viewing the original.
 233
 234
 235 HOW TO RESOLVE CONFLICTS
 236 ------------------------
 237
 238 After seeing a conflict, you can do two things:
 239
 240  * Decide not to merge.  The only clean-ups you need are to reset
 241    the index file to the `HEAD` commit to reverse 2. and to clean
 242    up working tree changes made by 2. and 3.; `git merge --abort`
 243    can be used for this.
 244
 245  * Resolve the conflicts.  Git will mark the conflicts in
 246    the working tree.  Edit the files into shape and
 247    'git add' them to the index.  Use 'git commit' to seal the deal.
 248
 249 You can work through the conflict with a number of tools:
 250
 251  * Use a mergetool.  `git mergetool` to launch a graphical
 252    mergetool which will work you through the merge.
 253
 254  * Look at the diffs.  `git diff` will show a three-way diff,
 255    highlighting changes from both the `HEAD` and `MERGE_HEAD`
 256    versions.
 257
 258  * Look at the diffs from each branch. `git log --merge -p <path>`
 259    will show diffs first for the `HEAD` version and then the
 260    `MERGE_HEAD` version.
 261
 262  * Look at the originals.  `git show :1:filename` shows the
 263    common ancestor, `git show :2:filename` shows the `HEAD`
 264    version, and `git show :3:filename` shows the `MERGE_HEAD`
 265    version.
 266
 267
 268 EXAMPLES
 269 --------
 270
 271 * Merge branches `fixes` and `enhancements` on top of
 272   the current branch, making an octopus merge:
 273 +
 274 ------------------------------------------------
 275 $ git merge fixes enhancements
 276 ------------------------------------------------
 277
 278 * Merge branch `obsolete` into the current branch, using `ours`
 279   merge strategy:
 280 +
 281 ------------------------------------------------
 282 $ git merge -s ours obsolete
 283 ------------------------------------------------
 284
 285 * Merge branch `maint` into the current branch, but do not make
 286   a new commit automatically:
 287 +
 288 ------------------------------------------------
 289 $ git merge --no-commit maint
 290 ------------------------------------------------
 291 +
 292 This can be used when you want to include further changes to the
 293 merge, or want to write your own merge commit message.
 294 +
 295 You should refrain from abusing this option to sneak substantial
 296 changes into a merge commit.  Small fixups like bumping
 297 release/version name would be acceptable.
 298
 299
 300 include::merge-strategies.txt[]
 301
 302 CONFIGURATION
 303 -------------
 304 include::merge-config.txt[]
 305
 306 branch.<name>.mergeoptions::
 307         Sets default options for merging into branch <name>. The syntax and
 308         supported options are the same as those of 'git merge', but option
 309         values containing whitespace characters are currently not supported.
 310
 311 SEE ALSO
 312 --------
 313 linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],
 314 linkgit:gitattributes[5],
 315 linkgit:git-reset[1],
 316 linkgit:git-diff[1], linkgit:git-ls-files[1],
 317 linkgit:git-add[1], linkgit:git-rm[1],
 318 linkgit:git-mergetool[1]
 319
 320 GIT
 321 ---
 322 Part of the linkgit:git[1] suite