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git/Documentation/revisions.txt

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SPECIFYING REVISIONS
--------------------
A revision parameter '<rev>' typically, but not necessarily, names a
commit object. It uses what is called an 'extended SHA-1'
syntax. Here are various ways to spell object names. The
ones listed near the end of this list name trees and
blobs contained in a commit.
NOTE: This document shows the "raw" syntax as seen by git. The shell
and other UIs might require additional quoting to protect special
characters and to avoid word splitting.
'<sha1>', e.g. 'dae86e1950b1277e545cee180551750029cfe735', 'dae86e'::
The full SHA-1 object name (40-byte hexadecimal string), or
a leading substring that is unique within the repository.
E.g. dae86e1950b1277e545cee180551750029cfe735 and dae86e both
name the same commit object if there is no other object in
your repository whose object name starts with dae86e.
'<describeOutput>', e.g. 'v1.7.4.2-679-g3bee7fb'::
Output from `git describe`; i.e. a closest tag, optionally
followed by a dash and a number of commits, followed by a dash, a
'g', and an abbreviated object name.
'<refname>', e.g. 'master', 'heads/master', 'refs/heads/master'::
A symbolic ref name. E.g. 'master' typically means the commit
object referenced by 'refs/heads/master'. If you
happen to have both 'heads/master' and 'tags/master', you can
explicitly say 'heads/master' to tell Git which one you mean.
When ambiguous, a '<refname>' is disambiguated by taking the
first match in the following rules:
. If '$GIT_DIR/<refname>' exists, that is what you mean (this is usually
useful only for `HEAD`, `FETCH_HEAD`, `ORIG_HEAD`, `MERGE_HEAD`
and `CHERRY_PICK_HEAD`);
. otherwise, 'refs/<refname>' if it exists;
. otherwise, 'refs/tags/<refname>' if it exists;
. otherwise, 'refs/heads/<refname>' if it exists;
. otherwise, 'refs/remotes/<refname>' if it exists;
. otherwise, 'refs/remotes/<refname>/HEAD' if it exists.
+
`HEAD` names the commit on which you based the changes in the working tree.
`FETCH_HEAD` records the branch which you fetched from a remote repository
with your last `git fetch` invocation.
`ORIG_HEAD` is created by commands that move your `HEAD` in a drastic
way, to record the position of the `HEAD` before their operation, so that
you can easily change the tip of the branch back to the state before you ran
them.
`MERGE_HEAD` records the commit(s) which you are merging into your branch
when you run `git merge`.
`CHERRY_PICK_HEAD` records the commit which you are cherry-picking
when you run `git cherry-pick`.
+
Note that any of the 'refs/*' cases above may come either from
the `$GIT_DIR/refs` directory or from the `$GIT_DIR/packed-refs` file.
While the ref name encoding is unspecified, UTF-8 is preferred as
some output processing may assume ref names in UTF-8.
'@'::
'@' alone is a shortcut for `HEAD`.
'[<refname>]@{<date>}', e.g. 'master@\{yesterday\}', 'HEAD@{5 minutes ago}'::
A ref followed by the suffix '@' with a date specification
enclosed in a brace
pair (e.g. '\{yesterday\}', '{1 month 2 weeks 3 days 1 hour 1
second ago}' or '{1979-02-26 18:30:00}') specifies the value
of the ref at a prior point in time. This suffix may only be
used immediately following a ref name and the ref must have an
existing log ('$GIT_DIR/logs/<ref>'). Note that this looks up the state
of your *local* ref at a given time; e.g., what was in your local
'master' branch last week. If you want to look at commits made during
certain times, see `--since` and `--until`.
'<refname>@{<n>}', e.g. 'master@\{1\}'::
A ref followed by the suffix '@' with an ordinal specification
enclosed in a brace pair (e.g. '\{1\}', '\{15\}') specifies
the n-th prior value of that ref. For example 'master@\{1\}'
is the immediate prior value of 'master' while 'master@\{5\}'
is the 5th prior value of 'master'. This suffix may only be used
immediately following a ref name and the ref must have an existing
log ('$GIT_DIR/logs/<refname>').
'@{<n>}', e.g. '@\{1\}'::
You can use the '@' construct with an empty ref part to get at a
reflog entry of the current branch. For example, if you are on
branch 'blabla' then '@\{1\}' means the same as 'blabla@\{1\}'.
'@{-<n>}', e.g. '@{-1}'::
The construct '@{-<n>}' means the <n>th branch/commit checked out
before the current one.
'[<branchname>]@\{upstream\}', e.g. 'master@\{upstream\}', '@\{u\}'::
A branch B may be set up to build on top of a branch X (configured with
`branch.<name>.merge`) at a remote R (configured with
`branch.<name>.remote`). B@{u} refers to the remote-tracking branch for
the branch X taken from remote R, typically found at `refs/remotes/R/X`.
'[<branchname>]@\{push\}', e.g. 'master@\{push\}', '@\{push\}'::
The suffix '@\{push}' reports the branch "where we would push to" if
`git push` were run while `branchname` was checked out (or the current
`HEAD` if no branchname is specified). Like for '@\{upstream\}', we report
the remote-tracking branch that corresponds to that branch at the remote.
+
Here's an example to make it more clear:
+
------------------------------
$ git config push.default current
$ git config remote.pushdefault myfork
$ git switch -c mybranch origin/master
$ git rev-parse --symbolic-full-name @{upstream}
refs/remotes/origin/master
$ git rev-parse --symbolic-full-name @{push}
refs/remotes/myfork/mybranch
------------------------------
+
Note in the example that we set up a triangular workflow, where we pull
from one location and push to another. In a non-triangular workflow,
'@\{push}' is the same as '@\{upstream}', and there is no need for it.
+
This suffix is also accepted when spelled in uppercase, and means the same
thing no matter the case.
'<rev>{caret}[<n>]', e.g. 'HEAD{caret}, v1.5.1{caret}0'::
A suffix '{caret}' to a revision parameter means the first parent of
that commit object. '{caret}<n>' means the <n>th parent (i.e.
'<rev>{caret}'
is equivalent to '<rev>{caret}1'). As a special rule,
'<rev>{caret}0' means the commit itself and is used when '<rev>' is the
object name of a tag object that refers to a commit object.
'<rev>{tilde}[<n>]', e.g. 'HEAD{tilde}, master{tilde}3'::
A suffix '{tilde}' to a revision parameter means the first parent of
that commit object.
A suffix '{tilde}<n>' to a revision parameter means the commit
object that is the <n>th generation ancestor of the named
commit object, following only the first parents. I.e. '<rev>{tilde}3' is
equivalent to '<rev>{caret}{caret}{caret}' which is equivalent to
'<rev>{caret}1{caret}1{caret}1'. See below for an illustration of
the usage of this form.
'<rev>{caret}{<type>}', e.g. 'v0.99.8{caret}\{commit\}'::
A suffix '{caret}' followed by an object type name enclosed in
brace pair means dereference the object at '<rev>' recursively until
an object of type '<type>' is found or the object cannot be
dereferenced anymore (in which case, barf).
For example, if '<rev>' is a commit-ish, '<rev>{caret}\{commit\}'
describes the corresponding commit object.
Similarly, if '<rev>' is a tree-ish, '<rev>{caret}\{tree\}'
describes the corresponding tree object.
'<rev>{caret}0'
is a short-hand for '<rev>{caret}\{commit\}'.
+
'<rev>{caret}\{object\}' can be used to make sure '<rev>' names an
object that exists, without requiring '<rev>' to be a tag, and
without dereferencing '<rev>'; because a tag is already an object,
it does not have to be dereferenced even once to get to an object.
+
'<rev>{caret}\{tag\}' can be used to ensure that '<rev>' identifies an
existing tag object.
'<rev>{caret}{}', e.g. 'v0.99.8{caret}{}'::
A suffix '{caret}' followed by an empty brace pair
means the object could be a tag,
and dereference the tag recursively until a non-tag object is
found.
'<rev>{caret}{/<text>}', e.g. 'HEAD^{/fix nasty bug}'::
A suffix '{caret}' to a revision parameter, followed by a brace
pair that contains a text led by a slash,
is the same as the ':/fix nasty bug' syntax below except that
it returns the youngest matching commit which is reachable from
the '<rev>' before '{caret}'.
':/<text>', e.g. ':/fix nasty bug'::
A colon, followed by a slash, followed by a text, names
a commit whose commit message matches the specified regular expression.
This name returns the youngest matching commit which is
reachable from any ref, including HEAD.
The regular expression can match any part of the
commit message. To match messages starting with a string, one can use
e.g. ':/^foo'. The special sequence ':/!' is reserved for modifiers to what
is matched. ':/!-foo' performs a negative match, while ':/!!foo' matches a
literal '!' character, followed by 'foo'. Any other sequence beginning with
':/!' is reserved for now.
Depending on the given text, the shell's word splitting rules might
require additional quoting.
'<rev>:<path>', e.g. 'HEAD:README', 'master:./README'::
A suffix ':' followed by a path names the blob or tree
at the given path in the tree-ish object named by the part
before the colon.
A path starting with './' or '../' is relative to the current working directory.
The given path will be converted to be relative to the working tree's root directory.
This is most useful to address a blob or tree from a commit or tree that has
the same tree structure as the working tree.
':[<n>:]<path>', e.g. ':0:README', ':README'::
A colon, optionally followed by a stage number (0 to 3) and a
colon, followed by a path, names a blob object in the
index at the given path. A missing stage number (and the colon
that follows it) names a stage 0 entry. During a merge, stage
1 is the common ancestor, stage 2 is the target branch's version
(typically the current branch), and stage 3 is the version from
the branch which is being merged.
Here is an illustration, by Jon Loeliger. Both commit nodes B
and C are parents of commit node A. Parent commits are ordered
left-to-right.
........................................
G H I J
\ / \ /
D E F
\ | / \
\ | / |
\|/ |
B C
\ /
\ /
A
........................................
A = = A^0
B = A^ = A^1 = A~1
C = = A^2
D = A^^ = A^1^1 = A~2
E = B^2 = A^^2
F = B^3 = A^^3
G = A^^^ = A^1^1^1 = A~3
H = D^2 = B^^2 = A^^^2 = A~2^2
I = F^ = B^3^ = A^^3^
J = F^2 = B^3^2 = A^^3^2
SPECIFYING RANGES
-----------------
History traversing commands such as `git log` operate on a set
of commits, not just a single commit.
For these commands,
specifying a single revision, using the notation described in the
previous section, means the set of commits `reachable` from the given
commit.
Specifying several revisions means the set of commits reachable from
any of the given commits.
A commit's reachable set is the commit itself and the commits in
its ancestry chain.
There are several notations to specify a set of connected commits
(called a "revision range"), illustrated below.
Commit Exclusions
~~~~~~~~~~~~~~~~~
'{caret}<rev>' (caret) Notation::
To exclude commits reachable from a commit, a prefix '{caret}'
notation is used. E.g. '{caret}r1 r2' means commits reachable
from 'r2' but exclude the ones reachable from 'r1' (i.e. 'r1' and
its ancestors).
Dotted Range Notations
~~~~~~~~~~~~~~~~~~~~~~
The '..' (two-dot) Range Notation::
The '{caret}r1 r2' set operation appears so often that there is a shorthand
for it. When you have two commits 'r1' and 'r2' (named according
to the syntax explained in SPECIFYING REVISIONS above), you can ask
for commits that are reachable from r2 excluding those that are reachable
from r1 by '{caret}r1 r2' and it can be written as 'r1..r2'.
The '\...' (three-dot) Symmetric Difference Notation::
A similar notation 'r1\...r2' is called symmetric difference
of 'r1' and 'r2' and is defined as
'r1 r2 --not $(git merge-base --all r1 r2)'.
It is the set of commits that are reachable from either one of
'r1' (left side) or 'r2' (right side) but not from both.
In these two shorthand notations, you can omit one end and let it default to HEAD.
For example, 'origin..' is a shorthand for 'origin..HEAD' and asks "What
did I do since I forked from the origin branch?" Similarly, '..origin'
is a shorthand for 'HEAD..origin' and asks "What did the origin do since
I forked from them?" Note that '..' would mean 'HEAD..HEAD' which is an
empty range that is both reachable and unreachable from HEAD.
Commands that are specifically designed to take two distinct ranges
(e.g. "git range-diff R1 R2" to compare two ranges) do exist, but
they are exceptions. Unless otherwise noted, all "git" commands
that operate on a set of commits work on a single revision range.
In other words, writing two "two-dot range notation" next to each
other, e.g.
$ git log A..B C..D
does *not* specify two revision ranges for most commands. Instead
it will name a single connected set of commits, i.e. those that are
reachable from either B or D but are reachable from neither A or C.
In a linear history like this:
---A---B---o---o---C---D
because A and B are reachable from C, the revision range specified
by these two dotted ranges is a single commit D.
Other <rev>{caret} Parent Shorthand Notations
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Three other shorthands exist, particularly useful for merge commits,
for naming a set that is formed by a commit and its parent commits.
The 'r1{caret}@' notation means all parents of 'r1'.
The 'r1{caret}!' notation includes commit 'r1' but excludes all of its parents.
By itself, this notation denotes the single commit 'r1'.
The '<rev>{caret}-[<n>]' notation includes '<rev>' but excludes the <n>th
parent (i.e. a shorthand for '<rev>{caret}<n>..<rev>'), with '<n>' = 1 if
not given. This is typically useful for merge commits where you
can just pass '<commit>{caret}-' to get all the commits in the branch
that was merged in merge commit '<commit>' (including '<commit>'
itself).
While '<rev>{caret}<n>' was about specifying a single commit parent, these
three notations also consider its parents. For example you can say
'HEAD{caret}2{caret}@', however you cannot say 'HEAD{caret}@{caret}2'.
Revision Range Summary
----------------------
'<rev>'::
Include commits that are reachable from <rev> (i.e. <rev> and its
ancestors).
'{caret}<rev>'::
Exclude commits that are reachable from <rev> (i.e. <rev> and its
ancestors).
'<rev1>..<rev2>'::
Include commits that are reachable from <rev2> but exclude
those that are reachable from <rev1>. When either <rev1> or
<rev2> is omitted, it defaults to `HEAD`.
'<rev1>\...<rev2>'::
Include commits that are reachable from either <rev1> or
<rev2> but exclude those that are reachable from both. When
either <rev1> or <rev2> is omitted, it defaults to `HEAD`.
'<rev>{caret}@', e.g. 'HEAD{caret}@'::
A suffix '{caret}' followed by an at sign is the same as listing
all parents of '<rev>' (meaning, include anything reachable from
its parents, but not the commit itself).
'<rev>{caret}!', e.g. 'HEAD{caret}!'::
A suffix '{caret}' followed by an exclamation mark is the same
as giving commit '<rev>' and then all its parents prefixed with
'{caret}' to exclude them (and their ancestors).
'<rev>{caret}-<n>', e.g. 'HEAD{caret}-, HEAD{caret}-2'::
Equivalent to '<rev>{caret}<n>..<rev>', with '<n>' = 1 if not
given.
Here are a handful of examples using the Loeliger illustration above,
with each step in the notation's expansion and selection carefully
spelt out:
....
Args Expanded arguments Selected commits
D G H D
D F G H I J D F
^G D H D
^D B E I J F B
^D B C E I J F B C
C I J F C
B..C = ^B C C
B...C = B ^F C G H D E B C
B^- = B^..B
= ^B^1 B E I J F B
C^@ = C^1
= F I J F
B^@ = B^1 B^2 B^3
= D E F D G H E F I J
C^! = C ^C^@
= C ^C^1
= C ^F C
B^! = B ^B^@
= B ^B^1 ^B^2 ^B^3
= B ^D ^E ^F B
F^! D = F ^I ^J D G H D F
....