merge(third_party/git): Merge squashed git subtree at v2.23.0 r/373

Merge commit '1b593e1ea4d2af0f6444d9a7788d5d99abd6fde5' as 'third_party/git'

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+git-show-ref(1)
+===============
+
+NAME
+----
+git-show-ref - List references in a local repository
+
+SYNOPSIS
+--------
+[verse]
+'git show-ref' [-q|--quiet] [--verify] [--head] [-d|--dereference]
+	     [-s|--hash[=<n>]] [--abbrev[=<n>]] [--tags]
+	     [--heads] [--] [<pattern>...]
+'git show-ref' --exclude-existing[=<pattern>]
+
+DESCRIPTION
+-----------
+
+Displays references available in a local repository along with the associated
+commit IDs. Results can be filtered using a pattern and tags can be
+dereferenced into object IDs. Additionally, it can be used to test whether a
+particular ref exists.
+
+By default, shows the tags, heads, and remote refs.
+
+The --exclude-existing form is a filter that does the inverse. It reads
+refs from stdin, one ref per line, and shows those that don't exist in
+the local repository.
+
+Use of this utility is encouraged in favor of directly accessing files under
+the `.git` directory.
+
+OPTIONS
+-------
+
+--head::
+
+	Show the HEAD reference, even if it would normally be filtered out.
+
+--heads::
+--tags::
+
+	Limit to "refs/heads" and "refs/tags", respectively.  These options
+	are not mutually exclusive; when given both, references stored in
+	"refs/heads" and "refs/tags" are displayed.
+
+-d::
+--dereference::
+
+	Dereference tags into object IDs as well. They will be shown with "{caret}{}"
+	appended.
+
+-s::
+--hash[=<n>]::
+
+	Only show the SHA-1 hash, not the reference name. When combined with
+	--dereference the dereferenced tag will still be shown after the SHA-1.
+
+--verify::
+
+	Enable stricter reference checking by requiring an exact ref path.
+	Aside from returning an error code of 1, it will also print an error
+	message if `--quiet` was not specified.
+
+--abbrev[=<n>]::
+
+	Abbreviate the object name.  When using `--hash`, you do
+	not have to say `--hash --abbrev`; `--hash=n` would do.
+
+-q::
+--quiet::
+
+	Do not print any results to stdout. When combined with `--verify` this
+	can be used to silently check if a reference exists.
+
+--exclude-existing[=<pattern>]::
+
+	Make 'git show-ref' act as a filter that reads refs from stdin of the
+	form "`^(?:<anything>\s)?<refname>(?:\^{})?$`"
+	and performs the following actions on each:
+	(1) strip "{caret}{}" at the end of line if any;
+	(2) ignore if pattern is provided and does not head-match refname;
+	(3) warn if refname is not a well-formed refname and skip;
+	(4) ignore if refname is a ref that exists in the local repository;
+	(5) otherwise output the line.
+
+
+<pattern>...::
+
+	Show references matching one or more patterns. Patterns are matched from
+	the end of the full name, and only complete parts are matched, e.g.
+	'master' matches 'refs/heads/master', 'refs/remotes/origin/master',
+	'refs/tags/jedi/master' but not 'refs/heads/mymaster' or
+	'refs/remotes/master/jedi'.
+
+OUTPUT
+------
+
+The output is in the format: '<SHA-1 ID>' '<space>' '<reference name>'.
+
+-----------------------------------------------------------------------------
+$ git show-ref --head --dereference
+832e76a9899f560a90ffd62ae2ce83bbeff58f54 HEAD
+832e76a9899f560a90ffd62ae2ce83bbeff58f54 refs/heads/master
+832e76a9899f560a90ffd62ae2ce83bbeff58f54 refs/heads/origin
+3521017556c5de4159da4615a39fa4d5d2c279b5 refs/tags/v0.99.9c
+6ddc0964034342519a87fe013781abf31c6db6ad refs/tags/v0.99.9c^{}
+055e4ae3ae6eb344cbabf2a5256a49ea66040131 refs/tags/v1.0rc4
+423325a2d24638ddcc82ce47be5e40be550f4507 refs/tags/v1.0rc4^{}
+...
+-----------------------------------------------------------------------------
+
+When using --hash (and not --dereference) the output format is: '<SHA-1 ID>'
+
+-----------------------------------------------------------------------------
+$ git show-ref --heads --hash
+2e3ba0114a1f52b47df29743d6915d056be13278
+185008ae97960c8d551adcd9e23565194651b5d1
+03adf42c988195b50e1a1935ba5fcbc39b2b029b
+...
+-----------------------------------------------------------------------------
+
+EXAMPLES
+--------
+
+To show all references called "master", whether tags or heads or anything
+else, and regardless of how deep in the reference naming hierarchy they are,
+use:
+
+-----------------------------------------------------------------------------
+	git show-ref master
+-----------------------------------------------------------------------------
+
+This will show "refs/heads/master" but also "refs/remote/other-repo/master",
+if such references exists.
+
+When using the `--verify` flag, the command requires an exact path:
+
+-----------------------------------------------------------------------------
+	git show-ref --verify refs/heads/master
+-----------------------------------------------------------------------------
+
+will only match the exact branch called "master".
+
+If nothing matches, 'git show-ref' will return an error code of 1,
+and in the case of verification, it will show an error message.
+
+For scripting, you can ask it to be quiet with the "--quiet" flag, which
+allows you to do things like
+
+-----------------------------------------------------------------------------
+	git show-ref --quiet --verify -- "refs/heads/$headname" ||
+		echo "$headname is not a valid branch"
+-----------------------------------------------------------------------------
+
+to check whether a particular branch exists or not (notice how we don't
+actually want to show any results, and we want to use the full refname for it
+in order to not trigger the problem with ambiguous partial matches).
+
+To show only tags, or only proper branch heads, use "--tags" and/or "--heads"
+respectively (using both means that it shows tags and heads, but not other
+random references under the refs/ subdirectory).
+
+To do automatic tag object dereferencing, use the "-d" or "--dereference"
+flag, so you can do
+
+-----------------------------------------------------------------------------
+	git show-ref --tags --dereference
+-----------------------------------------------------------------------------
+
+to get a listing of all tags together with what they dereference.
+
+FILES
+-----
+`.git/refs/*`, `.git/packed-refs`
+
+SEE ALSO
+--------
+linkgit:git-for-each-ref[1],
+linkgit:git-ls-remote[1],
+linkgit:git-update-ref[1],
+linkgit:gitrepository-layout[5]
+
+GIT
+---
+Part of the linkgit:git[1] suite