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         You need at least one <commit>.  Specifying more than one
  99         <commit> obviously means you are trying an Octopus.
 100
 101
 102 PRE-MERGE CHECKS
 103 ----------------
 104
 105 Before applying outside changes, you should get your own work in
 106 good shape and committed locally, so it will not be clobbered if
 107 there are conflicts.  See also linkgit:git-stash[1].
 108 'git pull' and 'git merge' will stop without doing anything when
 109 local uncommitted changes overlap with files that 'git pull'/'git
 110 merge' may need to update.
 111
 112 To avoid recording unrelated changes in the merge commit,
 113 'git pull' and 'git merge' will also abort if there are any changes
 114 registered in the index relative to the `HEAD` commit.  (One
 115 exception is when the changed index entries are in the state that
 116 would result from the merge already.)
 117
 118 If all named commits are already ancestors of `HEAD`, 'git merge'
 119 will exit early with the message "Already up-to-date."
 120
 121 FAST-FORWARD MERGE
 122 ------------------
 123
 124 Often the current branch head is an ancestor of the named commit.
 125 This is the most common case especially when invoked from 'git
 126 pull': you are tracking an upstream repository, you have committed
 127 no local changes, and now you want to update to a newer upstream
 128 revision.  In this case, a new commit is not needed to store the
 129 combined history; instead, the `HEAD` (along with the index) is
 130 updated to point at the named commit, without creating an extra
 131 merge commit.
 132
 133 This behavior can be suppressed with the `--no-ff` option.
 134
 135 TRUE MERGE
 136 ----------
 137
 138 Except in a fast-forward merge (see above), the branches to be
 139 merged must be tied together by a merge commit that has both of them
 140 as its parents.
 141
 142 A merged version reconciling the changes from all branches to be
 143 merged is committed, and your `HEAD`, index, and working tree are
 144 updated to it.  It is possible to have modifications in the working
 145 tree as long as they do not overlap; the update will preserve them.
 146
 147 When it is not obvious how to reconcile the changes, the following
 148 happens:
 149
 150 1. The `HEAD` pointer stays the same.
 151 2. The `MERGE_HEAD` ref is set to point to the other branch head.
 152 3. Paths that merged cleanly are updated both in the index file and
 153    in your working tree.
 154 4. For conflicting paths, the index file records up to three
 155    versions: stage 1 stores the version from the common ancestor,
 156    stage 2 from `HEAD`, and stage 3 from `MERGE_HEAD` (you
 157    can inspect the stages with `git ls-files -u`).  The working
 158    tree files contain the result of the "merge" program; i.e. 3-way
 159    merge results with familiar conflict markers `<<<` `===` `>>>`.
 160 5. No other changes are made.  In particular, the local
 161    modifications you had before you started merge will stay the
 162    same and the index entries for them stay as they were,
 163    i.e. matching `HEAD`.
 164
 165 If you tried a merge which resulted in complex conflicts and
 166 want to start over, you can recover with `git merge --abort`.
 167
 168 HOW CONFLICTS ARE PRESENTED
 169 ---------------------------
 170
 171 During a merge, the working tree files are updated to reflect the result
 172 of the merge.  Among the changes made to the common ancestor's version,
 173 non-overlapping ones (that is, you changed an area of the file while the
 174 other side left that area intact, or vice versa) are incorporated in the
 175 final result verbatim.  When both sides made changes to the same area,
 176 however, git cannot randomly pick one side over the other, and asks you to
 177 resolve it by leaving what both sides did to that area.
 178
 179 By default, git uses the same style as that is used by "merge" program
 180 from the RCS suite to present such a conflicted hunk, like this:
 181
 182 ------------
 183 Here are lines that are either unchanged from the common
 184 ancestor, or cleanly resolved because only one side changed.
 185 <<<<<<< yours:sample.txt
 186 Conflict resolution is hard;
 187 let's go shopping.
 188 =======
 189 Git makes conflict resolution easy.
 190 >>>>>>> theirs:sample.txt
 191 And here is another line that is cleanly resolved or unmodified.
 192 ------------
 193
 194 The area where a pair of conflicting changes happened is marked with markers
 195 `<<<<<<<`, `=======`, and `>>>>>>>`.  The part before the `=======`
 196 is typically your side, and the part afterwards is typically their side.
 197
 198 The default format does not show what the original said in the conflicting
 199 area.  You cannot tell how many lines are deleted and replaced with
 200 Barbie's remark on your side.  The only thing you can tell is that your
 201 side wants to say it is hard and you'd prefer to go shopping, while the
 202 other side wants to claim it is easy.
 203
 204 An alternative style can be used by setting the "merge.conflictstyle"
 205 configuration variable to "diff3".  In "diff3" style, the above conflict
 206 may look like this:
 207
 208 ------------
 209 Here are lines that are either unchanged from the common
 210 ancestor, or cleanly resolved because only one side changed.
 211 <<<<<<< yours:sample.txt
 212 Conflict resolution is hard;
 213 let's go shopping.
 214 |||||||
 215 Conflict resolution is hard.
 216 =======
 217 Git makes conflict resolution easy.
 218 >>>>>>> theirs:sample.txt
 219 And here is another line that is cleanly resolved or unmodified.
 220 ------------
 221
 222 In addition to the `<<<<<<<`, `=======`, and `>>>>>>>` markers, it uses
 223 another `|||||||` marker that is followed by the original text.  You can
 224 tell that the original just stated a fact, and your side simply gave in to
 225 that statement and gave up, while the other side tried to have a more
 226 positive attitude.  You can sometimes come up with a better resolution by
 227 viewing the original.
 228
 229
 230 HOW TO RESOLVE CONFLICTS
 231 ------------------------
 232
 233 After seeing a conflict, you can do two things:
 234
 235  * Decide not to merge.  The only clean-ups you need are to reset
 236    the index file to the `HEAD` commit to reverse 2. and to clean
 237    up working tree changes made by 2. and 3.; `git merge --abort`
 238    can be used for this.
 239
 240  * Resolve the conflicts.  Git will mark the conflicts in
 241    the working tree.  Edit the files into shape and
 242    'git add' them to the index.  Use 'git commit' to seal the deal.
 243
 244 You can work through the conflict with a number of tools:
 245
 246  * Use a mergetool.  `git mergetool` to launch a graphical
 247    mergetool which will work you through the merge.
 248
 249  * Look at the diffs.  `git diff` will show a three-way diff,
 250    highlighting changes from both the `HEAD` and `MERGE_HEAD`
 251    versions.
 252
 253  * Look at the diffs from each branch. `git log --merge -p <path>`
 254    will show diffs first for the `HEAD` version and then the
 255    `MERGE_HEAD` version.
 256
 257  * Look at the originals.  `git show :1:filename` shows the
 258    common ancestor, `git show :2:filename` shows the `HEAD`
 259    version, and `git show :3:filename` shows the `MERGE_HEAD`
 260    version.
 261
 262
 263 EXAMPLES
 264 --------
 265
 266 * Merge branches `fixes` and `enhancements` on top of
 267   the current branch, making an octopus merge:
 268 +
 269 ------------------------------------------------
 270 $ git merge fixes enhancements
 271 ------------------------------------------------
 272
 273 * Merge branch `obsolete` into the current branch, using `ours`
 274   merge strategy:
 275 +
 276 ------------------------------------------------
 277 $ git merge -s ours obsolete
 278 ------------------------------------------------
 279
 280 * Merge branch `maint` into the current branch, but do not make
 281   a new commit automatically:
 282 +
 283 ------------------------------------------------
 284 $ git merge --no-commit maint
 285 ------------------------------------------------
 286 +
 287 This can be used when you want to include further changes to the
 288 merge, or want to write your own merge commit message.
 289 +
 290 You should refrain from abusing this option to sneak substantial
 291 changes into a merge commit.  Small fixups like bumping
 292 release/version name would be acceptable.
 293
 294
 295 include::merge-strategies.txt[]
 296
 297 CONFIGURATION
 298 -------------
 299 include::merge-config.txt[]
 300
 301 branch.<name>.mergeoptions::
 302         Sets default options for merging into branch <name>. The syntax and
 303         supported options are the same as those of 'git merge', but option
 304         values containing whitespace characters are currently not supported.
 305
 306 SEE ALSO
 307 --------
 308 linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],
 309 linkgit:gitattributes[5],
 310 linkgit:git-reset[1],
 311 linkgit:git-diff[1], linkgit:git-ls-files[1],
 312 linkgit:git-add[1], linkgit:git-rm[1],
 313 linkgit:git-mergetool[1]
 314
 315 Author
 316 ------
 317 Written by Junio C Hamano <gitster@pobox.com>
 318
 319
 320 Documentation
 321 --------------
 322 Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
 323
 324 GIT
 325 ---
 326 Part of the linkgit:git[1] suite