t3507: introduce pristine-detach helper
[git/git.git] / 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 `$GIT_DIR/<name>` exists, that is what you mean (this is usually
28 useful only for `HEAD`, `FETCH_HEAD`, `ORIG_HEAD` and `MERGE_HEAD`);
29
30 . otherwise, `refs/<name>` if exists;
31
32 . otherwise, `refs/tags/<name>` if exists;
33
34 . otherwise, `refs/heads/<name>` if exists;
35
36 . otherwise, `refs/remotes/<name>` if exists;
37
38 . otherwise, `refs/remotes/<name>/HEAD` if exists.
39 +
40 HEAD names the commit your changes in the working tree is based on.
41 FETCH_HEAD records the branch you fetched from a remote repository
42 with your last 'git fetch' invocation.
43 ORIG_HEAD is created by commands that moves your HEAD in a drastic
44 way, to record the position of the HEAD before their operation, so that
45 you can change the tip of the branch back to the state before you ran
46 them easily.
47 MERGE_HEAD records the commit(s) you are merging into your branch
48 when you run 'git merge'.
49 +
50 Note that any of the `refs/*` cases above may come either from
51 the `$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 suffix '{caret}' to a revision parameter followed by a brace
110 pair that contains a text led by a slash (e.g. `HEAD^{/fix nasty bug}`):
111 this is the same as `:/fix nasty bug` syntax below except that
112 it returns the youngest matching commit which is reachable from
113 the ref before '{caret}'.
114
115 * A colon, followed by a slash, followed by a text (e.g. `:/fix nasty bug`): this names
116 a commit whose commit message matches the specified regular expression.
117 This name returns the youngest matching commit which is
118 reachable from any ref. If the commit message starts with a
119 '!', you have to repeat that; the special sequence ':/!',
120 followed by something else than '!' is reserved for now.
121 The regular expression can match any part of the commit message. To
122 match messages starting with a string, one can use e.g. `:/^foo`.
123
124 * A suffix ':' followed by a path (e.g. `HEAD:README`); this names the blob or tree
125 at the given path in the tree-ish object named by the part
126 before the colon.
127 ':path' (with an empty part before the colon, e.g. `:README`)
128 is a special case of the syntax described next: content
129 recorded in the index at the given path.
130 A path starting with './' or '../' is relative to current working directory.
131 The given path will be converted to be relative to working tree's root directory.
132 This is most useful to address a blob or tree from a commit or tree that has
133 the same tree structure with the working tree.
134
135 * A colon, optionally followed by a stage number (0 to 3) and a
136 colon, followed by a path (e.g. `:0:README`); this names a blob object in the
137 index at the given path. Missing stage number (and the colon
138 that follows it, e.g. `:README`) names a stage 0 entry. During a merge, stage
139 1 is the common ancestor, stage 2 is the target branch's version
140 (typically the current branch), and stage 3 is the version from
141 the branch being merged.
142
143 Here is an illustration, by Jon Loeliger. Both commit nodes B
144 and C are parents of commit node A. Parent commits are ordered
145 left-to-right.
146
147 ........................................
148 G H I J
149 \ / \ /
150 D E F
151 \ | / \
152 \ | / |
153 \|/ |
154 B C
155 \ /
156 \ /
157 A
158 ........................................
159
160 A = = A^0
161 B = A^ = A^1 = A~1
162 C = A^2 = A^2
163 D = A^^ = A^1^1 = A~2
164 E = B^2 = A^^2
165 F = B^3 = A^^3
166 G = A^^^ = A^1^1^1 = A~3
167 H = D^2 = B^^2 = A^^^2 = A~2^2
168 I = F^ = B^3^ = A^^3^
169 J = F^2 = B^3^2 = A^^3^2
170
171
172 SPECIFYING RANGES
173 -----------------
174
175 History traversing commands such as 'git log' operate on a set
176 of commits, not just a single commit. To these commands,
177 specifying a single revision with the notation described in the
178 previous section means the set of commits reachable from that
179 commit, following the commit ancestry chain.
180
181 To exclude commits reachable from a commit, a prefix `{caret}`
182 notation is used. E.g. `{caret}r1 r2` means commits reachable
183 from `r2` but exclude the ones reachable from `r1`.
184
185 This set operation appears so often that there is a shorthand
186 for it. When you have two commits `r1` and `r2` (named according
187 to the syntax explained in SPECIFYING REVISIONS above), you can ask
188 for commits that are reachable from r2 excluding those that are reachable
189 from r1 by `{caret}r1 r2` and it can be written as `r1..r2`.
190
191 A similar notation `r1\...r2` is called symmetric difference
192 of `r1` and `r2` and is defined as
193 `r1 r2 --not $(git merge-base --all r1 r2)`.
194 It is the set of commits that are reachable from either one of
195 `r1` or `r2` but not from both.
196
197 Two other shorthands for naming a set that is formed by a commit
198 and its parent commits exist. The `r1{caret}@` notation means all
199 parents of `r1`. `r1{caret}!` includes commit `r1` but excludes
200 all of its parents.
201
202 Here are a handful of examples:
203
204 D G H D
205 D F G H I J D F
206 ^G D H D
207 ^D B E I J F B
208 B...C G H D E B C
209 ^D B C E I J F B C
210 C^@ I J F
211 F^! D G H D F