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[git/git.git] / Documentation / revisions.txt
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1SPECIFYING REVISIONS
2--------------------
3
4A revision parameter typically, but not necessarily, names a
5commit object. They use what is called an 'extended SHA1'
6syntax. Here are various ways to spell object names. The
7ones listed near the end of this list are to name trees and
8blobs 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 `$GIT_DIR/<name>` exists, that is what you mean (this is usually
28 useful only for `HEAD`, `FETCH_HEAD`, `ORIG_HEAD` and `MERGE_HEAD`);
29
30 . otherwise, `refs/<name>` if exists;
31
32 . otherwise, `refs/tags/<name>` if exists;
33
34 . otherwise, `refs/heads/<name>` if exists;
35
36 . otherwise, `refs/remotes/<name>` if exists;
37
38 . otherwise, `refs/remotes/<name>/HEAD` if exists.
39+
40HEAD names the commit your changes in the working tree is based on.
41FETCH_HEAD records the branch you fetched from a remote repository
42with your last 'git fetch' invocation.
43ORIG_HEAD is created by commands that moves your HEAD in a drastic
44way, to record the position of the HEAD before their operation, so that
45you can change the tip of the branch back to the state before you ran
46them easily.
47MERGE_HEAD records the commit(s) you are merging into your branch
48when you run 'git merge'.
49+
50Note that any of the `refs/*` cases above may come either from
51the `$GIT_DIR/refs` directory or from the `$GIT_DIR/packed-refs` file.
52
53* A ref followed by the suffix '@' with a date specification
54 enclosed in a brace
55 pair (e.g. '\{yesterday\}', '\{1 month 2 weeks 3 days 1 hour 1
56 second ago\}' or '\{1979-02-26 18:30:00\}') to specify the value
57 of the ref at a prior point in time. This suffix may only be
58 used immediately following a ref name and the ref must have an
59 existing log ($GIT_DIR/logs/<ref>). Note that this looks up the state
60 of your *local* ref at a given time; e.g., what was in your local
61 `master` branch last week. If you want to look at commits made during
62 certain times, see `--since` and `--until`.
63
64* A ref followed by the suffix '@' with an ordinal specification
65 enclosed in a brace pair (e.g. '\{1\}', '\{15\}') to specify
66 the n-th prior value of that ref. For example 'master@\{1\}'
67 is the immediate prior value of 'master' while 'master@\{5\}'
68 is the 5th prior value of 'master'. This suffix may only be used
69 immediately following a ref name and the ref must have an existing
70 log ($GIT_DIR/logs/<ref>).
71
72* You can use the '@' construct with an empty ref part to get at a
73 reflog of the current branch. For example, if you are on the
74 branch 'blabla', then '@\{1\}' means the same as 'blabla@\{1\}'.
75
76* The special construct '@\{-<n>\}' means the <n>th branch checked out
77 before the current one.
78
79* The suffix '@\{upstream\}' to a ref (short form 'ref@\{u\}') refers to
80 the branch the ref is set to build on top of. Missing ref defaults
81 to the current branch.
82
83* A suffix '{caret}' to a revision parameter (e.g. 'HEAD{caret}') means the first parent of
84 that commit object. '{caret}<n>' means the <n>th parent (i.e.
85 'rev{caret}'
86 is equivalent to 'rev{caret}1'). As a special rule,
87 'rev{caret}0' means the commit itself and is used when 'rev' is the
88 object name of a tag object that refers to a commit object.
89
90* A suffix '{tilde}<n>' to a revision parameter means the commit
91 object that is the <n>th generation grand-parent of the named
92 commit object, following only the first parent. I.e. rev~3 is
93 equivalent to rev{caret}{caret}{caret} which is equivalent to
94 rev{caret}1{caret}1{caret}1. See below for a illustration of
95 the usage of this form.
96
97* A suffix '{caret}' followed by an object type name enclosed in
98 brace pair (e.g. `v0.99.8{caret}\{commit\}`) means the object
99 could be a tag, and dereference the tag recursively until an
100 object of that type is found or the object cannot be
101 dereferenced anymore (in which case, barf). `rev{caret}0`
102 introduced earlier is a short-hand for `rev{caret}\{commit\}`.
103
104* A suffix '{caret}' followed by an empty brace pair
105 (e.g. `v0.99.8{caret}\{\}`) means the object could be a tag,
106 and dereference the tag recursively until a non-tag object is
107 found.
108
109* A colon, followed by a slash, followed by a text (e.g. `:/fix nasty bug`): this names
110 a commit whose commit message starts with the specified text.
111 This name returns the youngest matching commit which is
112 reachable from any ref. If the commit message starts with a
113 '!', you have to repeat that; the special sequence ':/!',
114 followed by something else than '!' is reserved for now.
115
116* A suffix ':' followed by a path (e.g. `HEAD:README`); this names the blob or tree
117 at the given path in the tree-ish object named by the part
118 before the colon.
119 ':path' (with an empty part before the colon, e.g. `:README`)
120 is a special case of the syntax described next: content
121 recorded in the index at the given path.
122
123* A colon, optionally followed by a stage number (0 to 3) and a
124 colon, followed by a path (e.g. `:0:README`); this names a blob object in the
125 index at the given path. Missing stage number (and the colon
126 that follows it, e.g. `:README`) names a stage 0 entry. During a merge, stage
127 1 is the common ancestor, stage 2 is the target branch's version
128 (typically the current branch), and stage 3 is the version from
129 the branch being merged.
130
131Here is an illustration, by Jon Loeliger. Both commit nodes B
132and C are parents of commit node A. Parent commits are ordered
133left-to-right.
134
135........................................
136G H I J
137 \ / \ /
138 D E F
139 \ | / \
140 \ | / |
141 \|/ |
142 B C
143 \ /
144 \ /
145 A
146........................................
147
148 A = = A^0
149 B = A^ = A^1 = A~1
150 C = A^2 = A^2
151 D = A^^ = A^1^1 = A~2
152 E = B^2 = A^^2
153 F = B^3 = A^^3
154 G = A^^^ = A^1^1^1 = A~3
155 H = D^2 = B^^2 = A^^^2 = A~2^2
156 I = F^ = B^3^ = A^^3^
157 J = F^2 = B^3^2 = A^^3^2
158
159
160SPECIFYING RANGES
161-----------------
162
163History traversing commands such as 'git log' operate on a set
164of commits, not just a single commit. To these commands,
165specifying a single revision with the notation described in the
166previous section means the set of commits reachable from that
167commit, following the commit ancestry chain.
168
169To exclude commits reachable from a commit, a prefix `{caret}`
170notation is used. E.g. `{caret}r1 r2` means commits reachable
171from `r2` but exclude the ones reachable from `r1`.
172
173This set operation appears so often that there is a shorthand
174for it. When you have two commits `r1` and `r2` (named according
175to the syntax explained in SPECIFYING REVISIONS above), you can ask
176for commits that are reachable from r2 excluding those that are reachable
177from r1 by `{caret}r1 r2` and it can be written as `r1..r2`.
178
179A similar notation `r1\...r2` is called symmetric difference
180of `r1` and `r2` and is defined as
181`r1 r2 --not $(git merge-base --all r1 r2)`.
182It is the set of commits that are reachable from either one of
183`r1` or `r2` but not from both.
184
185Two other shorthands for naming a set that is formed by a commit
186and its parent commits exist. The `r1{caret}@` notation means all
187parents of `r1`. `r1{caret}!` includes commit `r1` but excludes
188all of its parents.
189
190Here are a handful of examples:
191
192 D G H D
193 D F G H I J D F
194 ^G D H D
195 ^D B E I J F B
196 B...C G H D E B C
197 ^D B C E I J F B C
198 C^@ I J F
199 F^! D G H D F