644eb60bd0
Sometimes users are given a hash of an object and they want to
identify it further (ex.: Use verify-pack to find the largest blobs,
but what are these? or [1])
When describing commits, we try to anchor them to tags or refs, as these
are conceptually on a higher level than the commit. And if there is no ref
or tag that matches exactly, we're out of luck. So we employ a heuristic
to make up a name for the commit. These names are ambiguous, there might
be different tags or refs to anchor to, and there might be different
path in the DAG to travel to arrive at the commit precisely.
When describing a blob, we want to describe the blob from a higher layer
as well, which is a tuple of (commit, deep/path) as the tree objects
involved are rather uninteresting. The same blob can be referenced by
multiple commits, so how we decide which commit to use? This patch
implements a rather naive approach on this: As there are no back pointers
from blobs to commits in which the blob occurs, we'll start walking from
any tips available, listing the blobs in-order of the commit and once we
found the blob, we'll take the first commit that listed the blob. For
example
git describe --tags v0.99:Makefile
conversion-901-g7672db20c2:Makefile
tells us the Makefile as it was in v0.99 was introduced in commit 7672db20.
The walking is performed in reverse order to show the introduction of a
blob rather than its last occurrence.
[1] https://stackoverflow.com/questions/223678/which-commit-has-this-blob
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
206 lines
7.7 KiB
Plaintext
206 lines
7.7 KiB
Plaintext
git-describe(1)
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===============
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NAME
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----
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git-describe - Give an object a human readable name based on an available ref
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SYNOPSIS
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--------
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[verse]
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'git describe' [--all] [--tags] [--contains] [--abbrev=<n>] [<commit-ish>...]
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'git describe' [--all] [--tags] [--contains] [--abbrev=<n>] --dirty[=<mark>]
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'git describe' <blob>
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DESCRIPTION
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-----------
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The command finds the most recent tag that is reachable from a
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commit. If the tag points to the commit, then only the tag is
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shown. Otherwise, it suffixes the tag name with the number of
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additional commits on top of the tagged object and the
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abbreviated object name of the most recent commit.
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By default (without --all or --tags) `git describe` only shows
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annotated tags. For more information about creating annotated tags
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see the -a and -s options to linkgit:git-tag[1].
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If the given object refers to a blob, it will be described
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as `<commit-ish>:<path>`, such that the blob can be found
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at `<path>` in the `<commit-ish>`, which itself describes the
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first commit in which this blob occurs in a reverse revision walk
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from HEAD.
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OPTIONS
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-------
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<commit-ish>...::
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Commit-ish object names to describe. Defaults to HEAD if omitted.
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--dirty[=<mark>]::
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--broken[=<mark>]::
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Describe the state of the working tree. When the working
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tree matches HEAD, the output is the same as "git describe
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HEAD". If the working tree has local modification "-dirty"
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is appended to it. If a repository is corrupt and Git
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cannot determine if there is local modification, Git will
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error out, unless `--broken' is given, which appends
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the suffix "-broken" instead.
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--all::
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Instead of using only the annotated tags, use any ref
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found in `refs/` namespace. This option enables matching
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any known branch, remote-tracking branch, or lightweight tag.
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--tags::
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Instead of using only the annotated tags, use any tag
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found in `refs/tags` namespace. This option enables matching
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a lightweight (non-annotated) tag.
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--contains::
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Instead of finding the tag that predates the commit, find
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the tag that comes after the commit, and thus contains it.
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Automatically implies --tags.
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--abbrev=<n>::
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Instead of using the default 7 hexadecimal digits as the
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abbreviated object name, use <n> digits, or as many digits
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as needed to form a unique object name. An <n> of 0
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will suppress long format, only showing the closest tag.
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--candidates=<n>::
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Instead of considering only the 10 most recent tags as
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candidates to describe the input commit-ish consider
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up to <n> candidates. Increasing <n> above 10 will take
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slightly longer but may produce a more accurate result.
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An <n> of 0 will cause only exact matches to be output.
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--exact-match::
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Only output exact matches (a tag directly references the
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supplied commit). This is a synonym for --candidates=0.
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--debug::
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Verbosely display information about the searching strategy
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being employed to standard error. The tag name will still
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be printed to standard out.
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--long::
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Always output the long format (the tag, the number of commits
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and the abbreviated commit name) even when it matches a tag.
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This is useful when you want to see parts of the commit object name
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in "describe" output, even when the commit in question happens to be
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a tagged version. Instead of just emitting the tag name, it will
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describe such a commit as v1.2-0-gdeadbee (0th commit since tag v1.2
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that points at object deadbee....).
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--match <pattern>::
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Only consider tags matching the given `glob(7)` pattern,
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excluding the "refs/tags/" prefix. If used with `--all`, it also
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considers local branches and remote-tracking references matching the
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pattern, excluding respectively "refs/heads/" and "refs/remotes/"
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prefix; references of other types are never considered. If given
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multiple times, a list of patterns will be accumulated, and tags
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matching any of the patterns will be considered. Use `--no-match` to
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clear and reset the list of patterns.
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--exclude <pattern>::
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Do not consider tags matching the given `glob(7)` pattern, excluding
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the "refs/tags/" prefix. If used with `--all`, it also does not consider
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local branches and remote-tracking references matching the pattern,
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excluding respectively "refs/heads/" and "refs/remotes/" prefix;
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references of other types are never considered. If given multiple times,
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a list of patterns will be accumulated and tags matching any of the
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patterns will be excluded. When combined with --match a tag will be
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considered when it matches at least one --match pattern and does not
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match any of the --exclude patterns. Use `--no-exclude` to clear and
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reset the list of patterns.
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--always::
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Show uniquely abbreviated commit object as fallback.
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--first-parent::
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Follow only the first parent commit upon seeing a merge commit.
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This is useful when you wish to not match tags on branches merged
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in the history of the target commit.
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EXAMPLES
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--------
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With something like git.git current tree, I get:
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[torvalds@g5 git]$ git describe parent
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v1.0.4-14-g2414721
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i.e. the current head of my "parent" branch is based on v1.0.4,
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but since it has a few commits on top of that,
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describe has added the number of additional commits ("14") and
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an abbreviated object name for the commit itself ("2414721")
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at the end.
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The number of additional commits is the number
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of commits which would be displayed by "git log v1.0.4..parent".
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The hash suffix is "-g" + 7-char abbreviation for the tip commit
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of parent (which was `2414721b194453f058079d897d13c4e377f92dc6`).
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The "g" prefix stands for "git" and is used to allow describing the version of
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a software depending on the SCM the software is managed with. This is useful
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in an environment where people may use different SCMs.
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Doing a 'git describe' on a tag-name will just show the tag name:
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[torvalds@g5 git]$ git describe v1.0.4
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v1.0.4
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With --all, the command can use branch heads as references, so
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the output shows the reference path as well:
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[torvalds@g5 git]$ git describe --all --abbrev=4 v1.0.5^2
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tags/v1.0.0-21-g975b
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[torvalds@g5 git]$ git describe --all --abbrev=4 HEAD^
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heads/lt/describe-7-g975b
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With --abbrev set to 0, the command can be used to find the
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closest tagname without any suffix:
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[torvalds@g5 git]$ git describe --abbrev=0 v1.0.5^2
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tags/v1.0.0
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Note that the suffix you get if you type these commands today may be
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longer than what Linus saw above when he ran these commands, as your
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Git repository may have new commits whose object names begin with
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975b that did not exist back then, and "-g975b" suffix alone may not
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be sufficient to disambiguate these commits.
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SEARCH STRATEGY
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---------------
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For each commit-ish supplied, 'git describe' will first look for
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a tag which tags exactly that commit. Annotated tags will always
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be preferred over lightweight tags, and tags with newer dates will
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always be preferred over tags with older dates. If an exact match
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is found, its name will be output and searching will stop.
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If an exact match was not found, 'git describe' will walk back
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through the commit history to locate an ancestor commit which
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has been tagged. The ancestor's tag will be output along with an
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abbreviation of the input commit-ish's SHA-1. If `--first-parent` was
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specified then the walk will only consider the first parent of each
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commit.
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If multiple tags were found during the walk then the tag which
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has the fewest commits different from the input commit-ish will be
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selected and output. Here fewest commits different is defined as
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the number of commits which would be shown by `git log tag..input`
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will be the smallest number of commits possible.
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BUGS
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----
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Tree objects as well as tag objects not pointing at commits, cannot be described.
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When describing blobs, the lightweight tags pointing at blobs are ignored,
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but the blob is still described as <committ-ish>:<path> despite the lightweight
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tag being favorable.
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GIT
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---
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Part of the linkgit:git[1] suite
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