Add new @ shortcut for HEAD
[git/git.git] / Documentation / revisions.txt
1 SPECIFYING REVISIONS
2 --------------------
3
4 A revision parameter '<rev>' typically, but not necessarily, names a
5 commit object. It uses what is called an 'extended SHA-1'
6 syntax. Here are various ways to spell object names. The
7 ones listed near the end of this list name trees and
8 blobs contained in a commit.
9
10 '<sha1>', e.g. 'dae86e1950b1277e545cee180551750029cfe735', 'dae86e'::
11 The full SHA-1 object name (40-byte hexadecimal string), or
12 a leading substring that is unique within the repository.
13 E.g. dae86e1950b1277e545cee180551750029cfe735 and dae86e both
14 name the same commit object if there is no other object in
15 your repository whose object name starts with dae86e.
16
17 '<describeOutput>', e.g. 'v1.7.4.2-679-g3bee7fb'::
18 Output from `git describe`; i.e. a closest tag, optionally
19 followed by a dash and a number of commits, followed by a dash, a
20 'g', and an abbreviated object name.
21
22 '<refname>', e.g. 'master', 'heads/master', 'refs/heads/master'::
23 A symbolic ref name. E.g. 'master' typically means the commit
24 object referenced by 'refs/heads/master'. If you
25 happen to have both 'heads/master' and 'tags/master', you can
26 explicitly say 'heads/master' to tell Git which one you mean.
27 When ambiguous, a '<refname>' is disambiguated by taking the
28 first match in the following rules:
29
30 . If '$GIT_DIR/<refname>' exists, that is what you mean (this is usually
31 useful only for 'HEAD', 'FETCH_HEAD', 'ORIG_HEAD', 'MERGE_HEAD'
32 and 'CHERRY_PICK_HEAD');
33
34 . otherwise, 'refs/<refname>' if it exists;
35
36 . otherwise, 'refs/tags/<refname>' if it exists;
37
38 . otherwise, 'refs/heads/<refname>' if it exists;
39
40 . otherwise, 'refs/remotes/<refname>' if it exists;
41
42 . otherwise, 'refs/remotes/<refname>/HEAD' if it exists.
43 +
44 'HEAD' names the commit on which you based the changes in the working tree.
45 'FETCH_HEAD' records the branch which you fetched from a remote repository
46 with your last `git fetch` invocation.
47 'ORIG_HEAD' is created by commands that move your 'HEAD' in a drastic
48 way, to record the position of the 'HEAD' before their operation, so that
49 you can easily change the tip of the branch back to the state before you ran
50 them.
51 'MERGE_HEAD' records the commit(s) which you are merging into your branch
52 when you run `git merge`.
53 'CHERRY_PICK_HEAD' records the commit which you are cherry-picking
54 when you run `git cherry-pick`.
55 +
56 Note that any of the 'refs/*' cases above may come either from
57 the '$GIT_DIR/refs' directory or from the '$GIT_DIR/packed-refs' file.
58 While the ref name encoding is unspecified, UTF-8 is preferred as
59 some output processing may assume ref names in UTF-8.
60
61 '@'::
62 '@' alone is a shortcut for 'HEAD'.
63
64 '<refname>@\{<date>\}', e.g. 'master@\{yesterday\}', 'HEAD@\{5 minutes ago\}'::
65 A ref followed by the suffix '@' with a date specification
66 enclosed in a brace
67 pair (e.g. '\{yesterday\}', '\{1 month 2 weeks 3 days 1 hour 1
68 second ago\}' or '\{1979-02-26 18:30:00\}') specifies the value
69 of the ref at a prior point in time. This suffix may only be
70 used immediately following a ref name and the ref must have an
71 existing log ('$GIT_DIR/logs/<ref>'). Note that this looks up the state
72 of your *local* ref at a given time; e.g., what was in your local
73 'master' branch last week. If you want to look at commits made during
74 certain times, see '--since' and '--until'.
75
76 '<refname>@\{<n>\}', e.g. 'master@\{1\}'::
77 A ref followed by the suffix '@' with an ordinal specification
78 enclosed in a brace pair (e.g. '\{1\}', '\{15\}') specifies
79 the n-th prior value of that ref. For example 'master@\{1\}'
80 is the immediate prior value of 'master' while 'master@\{5\}'
81 is the 5th prior value of 'master'. This suffix may only be used
82 immediately following a ref name and the ref must have an existing
83 log ('$GIT_DIR/logs/<refname>').
84
85 '@\{<n>\}', e.g. '@\{1\}'::
86 You can use the '@' construct with an empty ref part to get at a
87 reflog entry of the current branch. For example, if you are on
88 branch 'blabla' then '@\{1\}' means the same as 'blabla@\{1\}'.
89
90 '@\{-<n>\}', e.g. '@\{-1\}'::
91 The construct '@\{-<n>\}' means the <n>th branch checked out
92 before the current one.
93
94 '<branchname>@\{upstream\}', e.g. 'master@\{upstream\}', '@\{u\}'::
95 The suffix '@\{upstream\}' to a branchname (short form '<branchname>@\{u\}')
96 refers to the branch that the branch specified by branchname is set to build on
97 top of. A missing branchname defaults to the current one.
98
99 '<rev>{caret}', e.g. 'HEAD{caret}, v1.5.1{caret}0'::
100 A suffix '{caret}' to a revision parameter means the first parent of
101 that commit object. '{caret}<n>' means the <n>th parent (i.e.
102 '<rev>{caret}'
103 is equivalent to '<rev>{caret}1'). As a special rule,
104 '<rev>{caret}0' means the commit itself and is used when '<rev>' is the
105 object name of a tag object that refers to a commit object.
106
107 '<rev>{tilde}<n>', e.g. 'master{tilde}3'::
108 A suffix '{tilde}<n>' to a revision parameter means the commit
109 object that is the <n>th generation ancestor of the named
110 commit object, following only the first parents. I.e. '<rev>{tilde}3' is
111 equivalent to '<rev>{caret}{caret}{caret}' which is equivalent to
112 '<rev>{caret}1{caret}1{caret}1'. See below for an illustration of
113 the usage of this form.
114
115 '<rev>{caret}\{<type>\}', e.g. 'v0.99.8{caret}\{commit\}'::
116 A suffix '{caret}' followed by an object type name enclosed in
117 brace pair means the object
118 could be a tag, and dereference the tag recursively until an
119 object of that type is found or the object cannot be
120 dereferenced anymore (in which case, barf). '<rev>{caret}0'
121 is a short-hand for '<rev>{caret}\{commit\}'.
122 +
123 'rev{caret}\{object\}' can be used to make sure 'rev' names an
124 object that exists, without requiring 'rev' to be a tag, and
125 without dereferencing 'rev'; because a tag is already an object,
126 it does not have to be dereferenced even once to get to an object.
127
128 '<rev>{caret}\{\}', e.g. 'v0.99.8{caret}\{\}'::
129 A suffix '{caret}' followed by an empty brace pair
130 means the object could be a tag,
131 and dereference the tag recursively until a non-tag object is
132 found.
133
134 '<rev>{caret}\{/<text>\}', e.g. 'HEAD^{/fix nasty bug}'::
135 A suffix '{caret}' to a revision parameter, followed by a brace
136 pair that contains a text led by a slash,
137 is the same as the ':/fix nasty bug' syntax below except that
138 it returns the youngest matching commit which is reachable from
139 the '<rev>' before '{caret}'.
140
141 ':/<text>', e.g. ':/fix nasty bug'::
142 A colon, followed by a slash, followed by a text, names
143 a commit whose commit message matches the specified regular expression.
144 This name returns the youngest matching commit which is
145 reachable from any ref. If the commit message starts with a
146 '!' you have to repeat that; the special sequence ':/!',
147 followed by something else than '!', is reserved for now.
148 The regular expression can match any part of the commit message. To
149 match messages starting with a string, one can use e.g. ':/^foo'.
150
151 '<rev>:<path>', e.g. 'HEAD:README', ':README', 'master:./README'::
152 A suffix ':' followed by a path names the blob or tree
153 at the given path in the tree-ish object named by the part
154 before the colon.
155 ':path' (with an empty part before the colon)
156 is a special case of the syntax described next: content
157 recorded in the index at the given path.
158 A path starting with './' or '../' is relative to the current working directory.
159 The given path will be converted to be relative to the working tree's root directory.
160 This is most useful to address a blob or tree from a commit or tree that has
161 the same tree structure as the working tree.
162
163 ':<n>:<path>', e.g. ':0:README', ':README'::
164 A colon, optionally followed by a stage number (0 to 3) and a
165 colon, followed by a path, names a blob object in the
166 index at the given path. A missing stage number (and the colon
167 that follows it) names a stage 0 entry. During a merge, stage
168 1 is the common ancestor, stage 2 is the target branch's version
169 (typically the current branch), and stage 3 is the version from
170 the branch which is being merged.
171
172 Here is an illustration, by Jon Loeliger. Both commit nodes B
173 and C are parents of commit node A. Parent commits are ordered
174 left-to-right.
175
176 ........................................
177 G H I J
178 \ / \ /
179 D E F
180 \ | / \
181 \ | / |
182 \|/ |
183 B C
184 \ /
185 \ /
186 A
187 ........................................
188
189 A = = A^0
190 B = A^ = A^1 = A~1
191 C = A^2 = A^2
192 D = A^^ = A^1^1 = A~2
193 E = B^2 = A^^2
194 F = B^3 = A^^3
195 G = A^^^ = A^1^1^1 = A~3
196 H = D^2 = B^^2 = A^^^2 = A~2^2
197 I = F^ = B^3^ = A^^3^
198 J = F^2 = B^3^2 = A^^3^2
199
200
201 SPECIFYING RANGES
202 -----------------
203
204 History traversing commands such as `git log` operate on a set
205 of commits, not just a single commit. To these commands,
206 specifying a single revision with the notation described in the
207 previous section means the set of commits reachable from that
208 commit, following the commit ancestry chain.
209
210 To exclude commits reachable from a commit, a prefix '{caret}'
211 notation is used. E.g. '{caret}r1 r2' means commits reachable
212 from 'r2' but exclude the ones reachable from 'r1'.
213
214 This set operation appears so often that there is a shorthand
215 for it. When you have two commits 'r1' and 'r2' (named according
216 to the syntax explained in SPECIFYING REVISIONS above), you can ask
217 for commits that are reachable from r2 excluding those that are reachable
218 from r1 by '{caret}r1 r2' and it can be written as 'r1..r2'.
219
220 A similar notation 'r1\...r2' is called symmetric difference
221 of 'r1' and 'r2' and is defined as
222 'r1 r2 --not $(git merge-base --all r1 r2)'.
223 It is the set of commits that are reachable from either one of
224 'r1' or 'r2' but not from both.
225
226 In these two shorthands, you can omit one end and let it default to HEAD.
227 For example, 'origin..' is a shorthand for 'origin..HEAD' and asks "What
228 did I do since I forked from the origin branch?" Similarly, '..origin'
229 is a shorthand for 'HEAD..origin' and asks "What did the origin do since
230 I forked from them?" Note that '..' would mean 'HEAD..HEAD' which is an
231 empty range that is both reachable and unreachable from HEAD.
232
233 Two other shorthands for naming a set that is formed by a commit
234 and its parent commits exist. The 'r1{caret}@' notation means all
235 parents of 'r1'. 'r1{caret}!' includes commit 'r1' but excludes
236 all of its parents.
237
238 To summarize:
239
240 '<rev>'::
241 Include commits that are reachable from (i.e. ancestors of)
242 <rev>.
243
244 '{caret}<rev>'::
245 Exclude commits that are reachable from (i.e. ancestors of)
246 <rev>.
247
248 '<rev1>..<rev2>'::
249 Include commits that are reachable from <rev2> but exclude
250 those that are reachable from <rev1>. When either <rev1> or
251 <rev2> is omitted, it defaults to 'HEAD'.
252
253 '<rev1>\...<rev2>'::
254 Include commits that are reachable from either <rev1> or
255 <rev2> but exclude those that are reachable from both. When
256 either <rev1> or <rev2> is omitted, it defaults to 'HEAD'.
257
258 '<rev>{caret}@', e.g. 'HEAD{caret}@'::
259 A suffix '{caret}' followed by an at sign is the same as listing
260 all parents of '<rev>' (meaning, include anything reachable from
261 its parents, but not the commit itself).
262
263 '<rev>{caret}!', e.g. 'HEAD{caret}!'::
264 A suffix '{caret}' followed by an exclamation mark is the same
265 as giving commit '<rev>' and then all its parents prefixed with
266 '{caret}' to exclude them (and their ancestors).
267
268 Here are a handful of examples:
269
270 D G H D
271 D F G H I J D F
272 ^G D H D
273 ^D B E I J F B
274 B..C C
275 B...C G H D E B C
276 ^D B C E I J F B C
277 C I J F C
278 C^@ I J F
279 C^! C
280 F^! D G H D F