Documentation/revisions.txt

   1 SPECIFYING REVISIONS
   2 --------------------
   3
   4 A revision parameter typically, but not necessarily, names a
   5 commit object.  They use what is called an 'extended SHA1'
   6 syntax.  Here are various ways to spell object names.  The
   7 ones listed near the end of this list are to name trees and
   8 blobs contained in a commit.
   9
  10 * The full SHA1 object name (40-byte hexadecimal string), or
  11   a substring of such that is unique within the repository.
  12   E.g. dae86e1950b1277e545cee180551750029cfe735 and dae86e both
  13   name the same commit object if there are no other object in
  14   your repository whose object name starts with dae86e.
  15
  16 * An output from 'git describe'; i.e. a closest tag, optionally
  17   followed by a dash and a number of commits, followed by a dash, a
  18   `g`, and an abbreviated object name.
  19
  20 * A symbolic ref name.  E.g. 'master' typically means the commit
  21   object referenced by refs/heads/master.  If you
  22   happen to have both heads/master and tags/master, you can
  23   explicitly say 'heads/master' to tell git which one you mean.
  24   When ambiguous, a `<name>` is disambiguated by taking the
  25   first match in the following rules:
  26
  27   . if `$GIT_DIR/<name>` exists, that is what you mean (this is usually
  28     useful only for `HEAD`, `FETCH_HEAD`, `ORIG_HEAD`, `MERGE_HEAD`
  29     and `CHERRY_PICK_HEAD`);
  30
  31   . otherwise, `refs/<name>` if exists;
  32
  33   . otherwise, `refs/tags/<name>` if exists;
  34
  35   . otherwise, `refs/heads/<name>` if exists;
  36
  37   . otherwise, `refs/remotes/<name>` if exists;
  38
  39   . otherwise, `refs/remotes/<name>/HEAD` if exists.
  40 +
  41 HEAD names the commit your changes in the working tree is based on.
  42 FETCH_HEAD records the branch you fetched from a remote repository
  43 with your last 'git fetch' invocation.
  44 ORIG_HEAD is created by commands that moves your HEAD in a drastic
  45 way, to record the position of the HEAD before their operation, so that
  46 you can change the tip of the branch back to the state before you ran
  47 them easily.
  48 MERGE_HEAD records the commit(s) you are merging into your branch
  49 when you run 'git merge'.
  50 CHERRY_PICK_HEAD records the commit you are cherry-picking
  51 when you run 'git cherry-pick'.
  52 +
  53 Note that any of the `refs/*` cases above may come either from
  54 the `$GIT_DIR/refs` directory or from the `$GIT_DIR/packed-refs` file.
  55
  56 * A ref followed by the suffix '@' with a date specification
  57   enclosed in a brace
  58   pair (e.g. '\{yesterday\}', '\{1 month 2 weeks 3 days 1 hour 1
  59   second ago\}' or '\{1979-02-26 18:30:00\}') to specify the value
  60   of the ref at a prior point in time.  This suffix may only be
  61   used immediately following a ref name and the ref must have an
  62   existing log ($GIT_DIR/logs/<ref>). Note that this looks up the state
  63   of your *local* ref at a given time; e.g., what was in your local
  64   `master` branch last week. If you want to look at commits made during
  65   certain times, see `--since` and `--until`.
  66
  67 * A ref followed by the suffix '@' with an ordinal specification
  68   enclosed in a brace pair (e.g. '\{1\}', '\{15\}') to specify
  69   the n-th prior value of that ref.  For example 'master@\{1\}'
  70   is the immediate prior value of 'master' while 'master@\{5\}'
  71   is the 5th prior value of 'master'. This suffix may only be used
  72   immediately following a ref name and the ref must have an existing
  73   log ($GIT_DIR/logs/<ref>).
  74
  75 * You can use the '@' construct with an empty ref part to get at a
  76   reflog of the current branch. For example, if you are on the
  77   branch 'blabla', then '@\{1\}' means the same as 'blabla@\{1\}'.
  78
  79 * The special construct '@\{-<n>\}' means the <n>th branch checked out
  80   before the current one.
  81
  82 * The suffix '@\{upstream\}' to a ref (short form 'ref@\{u\}') refers to
  83   the branch the ref is set to build on top of.  Missing ref defaults
  84   to the current branch.
  85
  86 * A suffix '{caret}' to a revision parameter (e.g. 'HEAD{caret}') means the first parent of
  87   that commit object.  '{caret}<n>' means the <n>th parent (i.e.
  88   'rev{caret}'
  89   is equivalent to 'rev{caret}1').  As a special rule,
  90   'rev{caret}0' means the commit itself and is used when 'rev' is the
  91   object name of a tag object that refers to a commit object.
  92
  93 * A suffix '{tilde}<n>' to a revision parameter means the commit
  94   object that is the <n>th generation grand-parent of the named
  95   commit object, following only the first parent.  I.e. rev~3 is
  96   equivalent to rev{caret}{caret}{caret} which is equivalent to
  97   rev{caret}1{caret}1{caret}1.  See below for a illustration of
  98   the usage of this form.
  99
 100 * A suffix '{caret}' followed by an object type name enclosed in
 101   brace pair (e.g. `v0.99.8{caret}\{commit\}`) means the object
 102   could be a tag, and dereference the tag recursively until an
 103   object of that type is found or the object cannot be
 104   dereferenced anymore (in which case, barf).  `rev{caret}0`
 105   introduced earlier is a short-hand for `rev{caret}\{commit\}`.
 106
 107 * A suffix '{caret}' followed by an empty brace pair
 108   (e.g. `v0.99.8{caret}\{\}`) means the object could be a tag,
 109   and dereference the tag recursively until a non-tag object is
 110   found.
 111
 112 * A suffix '{caret}' to a revision parameter followed by a brace
 113   pair that contains a text led by a slash (e.g. `HEAD^{/fix nasty bug}`):
 114   this is the same as `:/fix nasty bug` syntax below except that
 115   it returns the youngest matching commit which is reachable from
 116   the ref before '{caret}'.
 117
 118 * A colon, followed by a slash, followed by a text (e.g. `:/fix nasty bug`): this names
 119   a commit whose commit message matches the specified regular expression.
 120   This name returns the youngest matching commit which is
 121   reachable from any ref.  If the commit message starts with a
 122   '!', you have to repeat that;  the special sequence ':/!',
 123   followed by something else than '!' is reserved for now.
 124   The regular expression can match any part of the commit message. To
 125   match messages starting with a string, one can use e.g. `:/^foo`.
 126
 127 * A suffix ':' followed by a path (e.g. `HEAD:README`); this names the blob or tree
 128   at the given path in the tree-ish object named by the part
 129   before the colon.
 130   ':path' (with an empty part before the colon, e.g. `:README`)
 131   is a special case of the syntax described next: content
 132   recorded in the index at the given path.
 133   A path starting with './' or '../' is relative to current working directory.
 134   The given path will be converted to be relative to working tree's root directory.
 135   This is most useful to address a blob or tree from a commit or tree that has
 136   the same tree structure with the working tree.
 137
 138 * A colon, optionally followed by a stage number (0 to 3) and a
 139   colon, followed by a path (e.g. `:0:README`); this names a blob object in the
 140   index at the given path. Missing stage number (and the colon
 141   that follows it, e.g. `:README`) names a stage 0 entry. During a merge, stage
 142   1 is the common ancestor, stage 2 is the target branch's version
 143   (typically the current branch), and stage 3 is the version from
 144   the branch being merged.
 145
 146 Here is an illustration, by Jon Loeliger.  Both commit nodes B
 147 and C are parents of commit node A.  Parent commits are ordered
 148 left-to-right.
 149
 150 ........................................
 151 G   H   I   J
 152  \ /     \ /
 153   D   E   F
 154    \  |  / \
 155     \ | /   |
 156      \|/    |
 157       B     C
 158        \   /
 159         \ /
 160          A
 161 ........................................
 162
 163     A =      = A^0
 164     B = A^   = A^1     = A~1
 165     C = A^2  = A^2
 166     D = A^^  = A^1^1   = A~2
 167     E = B^2  = A^^2
 168     F = B^3  = A^^3
 169     G = A^^^ = A^1^1^1 = A~3
 170     H = D^2  = B^^2    = A^^^2  = A~2^2
 171     I = F^   = B^3^    = A^^3^
 172     J = F^2  = B^3^2   = A^^3^2
 173
 174
 175 SPECIFYING RANGES
 176 -----------------
 177
 178 History traversing commands such as 'git log' operate on a set
 179 of commits, not just a single commit.  To these commands,
 180 specifying a single revision with the notation described in the
 181 previous section means the set of commits reachable from that
 182 commit, following the commit ancestry chain.
 183
 184 To exclude commits reachable from a commit, a prefix `{caret}`
 185 notation is used.  E.g. `{caret}r1 r2` means commits reachable
 186 from `r2` but exclude the ones reachable from `r1`.
 187
 188 This set operation appears so often that there is a shorthand
 189 for it.  When you have two commits `r1` and `r2` (named according
 190 to the syntax explained in SPECIFYING REVISIONS above), you can ask
 191 for commits that are reachable from r2 excluding those that are reachable
 192 from r1 by `{caret}r1 r2` and it can be written as `r1..r2`.
 193
 194 A similar notation `r1\...r2` is called symmetric difference
 195 of `r1` and `r2` and is defined as
 196 `r1 r2 --not $(git merge-base --all r1 r2)`.
 197 It is the set of commits that are reachable from either one of
 198 `r1` or `r2` but not from both.
 199
 200 Two other shorthands for naming a set that is formed by a commit
 201 and its parent commits exist.  The `r1{caret}@` notation means all
 202 parents of `r1`.  `r1{caret}!` includes commit `r1` but excludes
 203 all of its parents.
 204
 205 Here are a handful of examples:
 206
 207    D                G H D
 208    D F              G H I J D F
 209    ^G D             H D
 210    ^D B             E I J F B
 211    B...C            G H D E B C
 212    ^D B C           E I J F B C
 213    C^@              I J F
 214    F^! D            G H D F