Documentation/git-rev-parse.txt - jrn/git - Git at Google

 git-rev-parse(1)
 ================

 NAME
 ----
 git-rev-parse - Pick out and massage parameters


 SYNOPSIS
 --------
 'git rev-parse' [ --option ] <args>...

 DESCRIPTION
 -----------

 Many git porcelainish commands take mixture of flags
 (i.e. parameters that begin with a dash '-') and parameters
 meant for the underlying 'git-rev-list' command they use internally
 and flags and parameters for the other commands they use
 downstream of 'git-rev-list'.  This command is used to
 distinguish between them.


 OPTIONS
 -------
 --parseopt::
 	Use 'git-rev-parse' in option parsing mode (see PARSEOPT section below).

 --keep-dash-dash::
 	Only meaningful in `--parseopt` mode. Tells the option parser to echo
 	out the first `--` met instead of skipping it.

 --revs-only::
 	Do not output flags and parameters not meant for
 	'git-rev-list' command.

 --no-revs::
 	Do not output flags and parameters meant for
 	'git-rev-list' command.

 --flags::
 	Do not output non-flag parameters.

 --no-flags::
 	Do not output flag parameters.

 --default <arg>::
 	If there is no parameter given by the user, use `<arg>`
 	instead.

 --verify::
 	The parameter given must be usable as a single, valid
 	object name.  Otherwise barf and abort.

 -q::
 --quiet::
 	Only meaningful in `--verify` mode. Do not output an error
 	message if the first argument is not a valid object name;
 	instead exit with non-zero status silently.

 --sq::
 	Usually the output is made one line per flag and
 	parameter.  This option makes output a single line,
 	properly quoted for consumption by shell.  Useful when
 	you expect your parameter to contain whitespaces and
 	newlines (e.g. when using pickaxe `-S` with
 	'git-diff-\*').

 --not::
 	When showing object names, prefix them with '{caret}' and
 	strip '{caret}' prefix from the object names that already have
 	one.

 --symbolic::
 	Usually the object names are output in SHA1 form (with
 	possible '{caret}' prefix); this option makes them output in a
 	form as close to the original input as possible.

 --symbolic-full-name::
 	This is similar to \--symbolic, but it omits input that
 	are not refs (i.e. branch or tag names; or more
 	explicitly disambiguating "heads/master" form, when you
 	want to name the "master" branch when there is an
 	unfortunately named tag "master"), and show them as full
 	refnames (e.g. "refs/heads/master").

 --all::
 	Show all refs found in `$GIT_DIR/refs`.

 --branches::
 	Show branch refs found in `$GIT_DIR/refs/heads`.

 --tags::
 	Show tag refs found in `$GIT_DIR/refs/tags`.

 --remotes::
 	Show tag refs found in `$GIT_DIR/refs/remotes`.

 --show-prefix::
 	When the command is invoked from a subdirectory, show the
 	path of the current directory relative to the top-level
 	directory.

 --show-cdup::
 	When the command is invoked from a subdirectory, show the
 	path of the top-level directory relative to the current
 	directory (typically a sequence of "../", or an empty string).

 --git-dir::
 	Show `$GIT_DIR` if defined else show the path to the .git directory.

 --is-inside-git-dir::
 	When the current working directory is below the repository
 	directory print "true", otherwise "false".

 --is-inside-work-tree::
 	When the current working directory is inside the work tree of the
 	repository print "true", otherwise "false".

 --is-bare-repository::
 	When the repository is bare print "true", otherwise "false".

 --short::
 --short=number::
 	Instead of outputting the full SHA1 values of object names try to
 	abbreviate them to a shorter unique name. When no length is specified
 	7 is used. The minimum length is 4.

 --since=datestring::
 --after=datestring::
 	Parse the date string, and output the corresponding
 	--max-age= parameter for 'git-rev-list'.

 --until=datestring::
 --before=datestring::
 	Parse the date string, and output the corresponding
 	--min-age= parameter for 'git-rev-list'.

 <args>...::
 	Flags and parameters to be parsed.


 SPECIFYING REVISIONS
 --------------------

 A revision parameter typically, but not necessarily, names a
 commit object.  They use what is called an 'extended SHA1'
 syntax.  Here are various ways to spell object names.  The
 ones listed near the end of this list are to name trees and
 blobs contained in a commit.

 * The full SHA1 object name (40-byte hexadecimal string), or
   a substring of such that is unique within the repository.
   E.g. dae86e1950b1277e545cee180551750029cfe735 and dae86e both
   name the same commit object if there are no other object in
   your repository whose object name starts with dae86e.

 * An 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.

 * A symbolic ref name.  E.g. 'master' typically means the commit
   object referenced by $GIT_DIR/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 `<name>` is disambiguated by taking the
   first match in the following rules:

   . if `$GIT_DIR/<name>` exists, that is what you mean (this is usually
     useful only for `HEAD`, `FETCH_HEAD`, `ORIG_HEAD` and `MERGE_HEAD`);

   . otherwise, `$GIT_DIR/refs/<name>` if exists;

   . otherwise, `$GIT_DIR/refs/tags/<name>` if exists;

   . otherwise, `$GIT_DIR/refs/heads/<name>` if exists;

   . otherwise, `$GIT_DIR/refs/remotes/<name>` if exists;

   . otherwise, `$GIT_DIR/refs/remotes/<name>/HEAD` if exists.
 +
 HEAD names the commit your changes in the working tree is based on.
 FETCH_HEAD records the branch you fetched from a remote repository
 with your last 'git-fetch' invocation.
 ORIG_HEAD is created by commands that moves your HEAD in a drastic
 way, to record the position of the HEAD before their operation, so that
 you can change the tip of the branch back to the state before you ran
 them easily.
 MERGE_HEAD records the commit(s) you are merging into your branch
 when you run 'git-merge'.

 * 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\}') to specify 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`.

 * A ref followed by the suffix '@' with an ordinal specification
   enclosed in a brace pair (e.g. '\{1\}', '\{15\}') to specify
   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/<ref>).

 * You can use the '@' construct with an empty ref part to get at a
   reflog of the current branch. For example, if you are on the
   branch 'blabla', then '@\{1\}' means the same as 'blabla@\{1\}'.

 * The special construct '@\{-<n>\}' means the <n>th branch checked out
   before the current one.

 * 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.

 * A suffix '{tilde}<n>' to a revision parameter means the commit
   object that is the <n>th generation grand-parent of the named
   commit object, following only the first parent.  I.e. rev~3 is
   equivalent to rev{caret}{caret}{caret} which is equivalent to
   rev{caret}1{caret}1{caret}1.  See below for a illustration of
   the usage of this form.

 * A suffix '{caret}' followed by an object type name enclosed in
   brace pair (e.g. `v0.99.8{caret}\{commit\}`) means the object
   could be a tag, and dereference the tag recursively until an
   object of that type is found or the object cannot be
   dereferenced anymore (in which case, barf).  `rev{caret}0`
   introduced earlier is a short-hand for `rev{caret}\{commit\}`.

 * A suffix '{caret}' followed by an empty brace pair
   (e.g. `v0.99.8{caret}\{\}`) means the object could be a tag,
   and dereference the tag recursively until a non-tag object is
   found.

 * A colon, followed by a slash, followed by a text: this names
   a commit whose commit message starts with the specified text.
   This name returns the youngest matching commit which is
   reachable from any ref.  If the commit message starts with a
   '!', you have to repeat that;  the special sequence ':/!',
   followed by something else than '!' is reserved for now.

 * A suffix ':' followed by a path; this names the blob or tree
   at the given path in the tree-ish object named by the part
   before the colon.

 * A colon, optionally followed by a stage number (0 to 3) and a
   colon, followed by a path; this names a blob object in the
   index at the given path.  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 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  = 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.  To these commands,
 specifying a single revision with the notation described in the
 previous section means the set of commits reachable from that
 commit, following the commit ancestry chain.

 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`.

 This 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`.

 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` or `r2` but not from both.

 Two other shorthands for naming a set that is formed by a commit
 and its parent commits exist.  The `r1{caret}@` notation means all
 parents of `r1`.  `r1{caret}!` includes commit `r1` but excludes
 all of its parents.

 Here are a handful of examples:

    D                G H D
    D F              G H I J D F
    ^G D             H D
    ^D B             E I J F B
    B...C            G H D E B C
    ^D B C           E I J F B C
    C^@              I J F
    F^! D            G H D F

 PARSEOPT
 --------

 In `--parseopt` mode, 'git-rev-parse' helps massaging options to bring to shell
 scripts the same facilities C builtins have. It works as an option normalizer
 (e.g. splits single switches aggregate values), a bit like `getopt(1)` does.

 It takes on the standard input the specification of the options to parse and
 understand, and echoes on the standard output a line suitable for `sh(1)` `eval`
 to replace the arguments with normalized ones.  In case of error, it outputs
 usage on the standard error stream, and exits with code 129.

 Input Format
 ~~~~~~~~~~~~

 'git-rev-parse --parseopt' input format is fully text based. It has two parts,
 separated by a line that contains only `--`. The lines before the separator
 (should be more than one) are used for the usage.
 The lines after the separator describe the options.

 Each line of options has this format:

 ------------
 <opt_spec><flags>* SP+ help LF
 ------------

 `<opt_spec>`::
 	its format is the short option character, then the long option name
 	separated by a comma. Both parts are not required, though at least one
 	is necessary. `h,help`, `dry-run` and `f` are all three correct
 	`<opt_spec>`.

 `<flags>`::
 	`<flags>` are of `*`, `=`, `?` or `!`.
 	* Use `=` if the option takes an argument.

 	* Use `?` to mean that the option is optional (though its use is discouraged).

 	* Use `*` to mean that this option should not be listed in the usage
 	  generated for the `-h` argument. It's shown for `--help-all` as
 	  documented in linkgit:gitcli[7].

 	* Use `!` to not make the corresponding negated long option available.

 The remainder of the line, after stripping the spaces, is used
 as the help associated to the option.

 Blank lines are ignored, and lines that don't match this specification are used
 as option group headers (start the line with a space to create such
 lines on purpose).

 Example
 ~~~~~~~

 ------------
 OPTS_SPEC="\
 some-command [options] <args>...

 some-command does foo and bar!
 --
 h,help    show the help

 foo       some nifty option --foo
 bar=      some cool option --bar with an argument

   An option group Header
 C?        option C with an optional argument"

 eval `echo "$OPTS_SPEC" | git rev-parse --parseopt -- "$@" || echo exit $?`
 ------------

 EXAMPLES
 --------

 * Print the object name of the current commit:
 +
 ------------
 $ git rev-parse --verify HEAD
 ------------

 * Print the commit object name from the revision in the $REV shell variable:
 +
 ------------
 $ git rev-parse --verify $REV
 ------------
 +
 This will error out if $REV is empty or not a valid revision.

 * Same as above:
 +
 ------------
 $ git rev-parse --default master --verify $REV
 ------------
 +
 but if $REV is empty, the commit object name from master will be printed.


 Author
 ------
 Written by Linus Torvalds <torvalds@osdl.org> .
 Junio C Hamano <gitster@pobox.com> and Pierre Habouzit <madcoder@debian.org>

 Documentation
 --------------
 Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.

 GIT
 ---
 Part of the linkgit:git[1] suite
	git-rev-parse(1)
	================

	NAME
	----
	git-rev-parse - Pick out and massage parameters


	SYNOPSIS
	--------
	'git rev-parse' [ --option ] <args>...

	DESCRIPTION
	-----------

	Many git porcelainish commands take mixture of flags
	(i.e. parameters that begin with a dash '-') and parameters
	meant for the underlying 'git-rev-list' command they use internally
	and flags and parameters for the other commands they use
	downstream of 'git-rev-list'. This command is used to
	distinguish between them.


	OPTIONS
	-------
	--parseopt::
	Use 'git-rev-parse' in option parsing mode (see PARSEOPT section below).

	--keep-dash-dash::
	Only meaningful in `--parseopt` mode. Tells the option parser to echo
	out the first `--` met instead of skipping it.

	--revs-only::
	Do not output flags and parameters not meant for
	'git-rev-list' command.

	--no-revs::
	Do not output flags and parameters meant for
	'git-rev-list' command.

	--flags::
	Do not output non-flag parameters.

	--no-flags::
	Do not output flag parameters.

	--default <arg>::
	If there is no parameter given by the user, use `<arg>`
	instead.

	--verify::
	The parameter given must be usable as a single, valid
	object name. Otherwise barf and abort.

	-q::
	--quiet::
	Only meaningful in `--verify` mode. Do not output an error
	message if the first argument is not a valid object name;
	instead exit with non-zero status silently.

	--sq::
	Usually the output is made one line per flag and
	parameter. This option makes output a single line,
	properly quoted for consumption by shell. Useful when
	you expect your parameter to contain whitespaces and
	newlines (e.g. when using pickaxe `-S` with
	'git-diff-\*').

	--not::
	When showing object names, prefix them with '{caret}' and
	strip '{caret}' prefix from the object names that already have
	one.

	--symbolic::
	Usually the object names are output in SHA1 form (with
	possible '{caret}' prefix); this option makes them output in a
	form as close to the original input as possible.

	--symbolic-full-name::
	This is similar to \--symbolic, but it omits input that
	are not refs (i.e. branch or tag names; or more
	explicitly disambiguating "heads/master" form, when you
	want to name the "master" branch when there is an
	unfortunately named tag "master"), and show them as full
	refnames (e.g. "refs/heads/master").

	--all::
	Show all refs found in `$GIT_DIR/refs`.

	--branches::
	Show branch refs found in `$GIT_DIR/refs/heads`.

	--tags::
	Show tag refs found in `$GIT_DIR/refs/tags`.

	--remotes::
	Show tag refs found in `$GIT_DIR/refs/remotes`.

	--show-prefix::
	When the command is invoked from a subdirectory, show the
	path of the current directory relative to the top-level
	directory.

	--show-cdup::
	When the command is invoked from a subdirectory, show the
	path of the top-level directory relative to the current
	directory (typically a sequence of "../", or an empty string).

	--git-dir::
	Show `$GIT_DIR` if defined else show the path to the .git directory.

	--is-inside-git-dir::
	When the current working directory is below the repository
	directory print "true", otherwise "false".

	--is-inside-work-tree::
	When the current working directory is inside the work tree of the
	repository print "true", otherwise "false".

	--is-bare-repository::
	When the repository is bare print "true", otherwise "false".

	--short::
	--short=number::
	Instead of outputting the full SHA1 values of object names try to
	abbreviate them to a shorter unique name. When no length is specified
	7 is used. The minimum length is 4.

	--since=datestring::
	--after=datestring::
	Parse the date string, and output the corresponding
	--max-age= parameter for 'git-rev-list'.

	--until=datestring::
	--before=datestring::
	Parse the date string, and output the corresponding
	--min-age= parameter for 'git-rev-list'.

	<args>...::
	Flags and parameters to be parsed.


	SPECIFYING REVISIONS
	--------------------

	A revision parameter typically, but not necessarily, names a
	commit object. They use what is called an 'extended SHA1'
	syntax. Here are various ways to spell object names. The
	ones listed near the end of this list are to name trees and
	blobs contained in a commit.

	* The full SHA1 object name (40-byte hexadecimal string), or
	a substring of such that is unique within the repository.
	E.g. dae86e1950b1277e545cee180551750029cfe735 and dae86e both
	name the same commit object if there are no other object in
	your repository whose object name starts with dae86e.

	* An 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.

	* A symbolic ref name. E.g. 'master' typically means the commit
	object referenced by $GIT_DIR/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 `<name>` is disambiguated by taking the
	first match in the following rules:

	. if `$GIT_DIR/<name>` exists, that is what you mean (this is usually
	useful only for `HEAD`, `FETCH_HEAD`, `ORIG_HEAD` and `MERGE_HEAD`);

	. otherwise, `$GIT_DIR/refs/<name>` if exists;

	. otherwise, `$GIT_DIR/refs/tags/<name>` if exists;

	. otherwise, `$GIT_DIR/refs/heads/<name>` if exists;

	. otherwise, `$GIT_DIR/refs/remotes/<name>` if exists;

	. otherwise, `$GIT_DIR/refs/remotes/<name>/HEAD` if exists.
	+
	HEAD names the commit your changes in the working tree is based on.
	FETCH_HEAD records the branch you fetched from a remote repository
	with your last 'git-fetch' invocation.
	ORIG_HEAD is created by commands that moves your HEAD in a drastic
	way, to record the position of the HEAD before their operation, so that
	you can change the tip of the branch back to the state before you ran
	them easily.
	MERGE_HEAD records the commit(s) you are merging into your branch
	when you run 'git-merge'.

	* 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\}') to specify 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`.

	* A ref followed by the suffix '@' with an ordinal specification
	enclosed in a brace pair (e.g. '\{1\}', '\{15\}') to specify
	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/<ref>).

	* You can use the '@' construct with an empty ref part to get at a
	reflog of the current branch. For example, if you are on the
	branch 'blabla', then '@\{1\}' means the same as 'blabla@\{1\}'.

	* The special construct '@\{-<n>\}' means the <n>th branch checked out
	before the current one.

	* 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.

	* A suffix '{tilde}<n>' to a revision parameter means the commit
	object that is the <n>th generation grand-parent of the named
	commit object, following only the first parent. I.e. rev~3 is
	equivalent to rev{caret}{caret}{caret} which is equivalent to
	rev{caret}1{caret}1{caret}1. See below for a illustration of
	the usage of this form.

	* A suffix '{caret}' followed by an object type name enclosed in
	brace pair (e.g. `v0.99.8{caret}\{commit\}`) means the object
	could be a tag, and dereference the tag recursively until an
	object of that type is found or the object cannot be
	dereferenced anymore (in which case, barf). `rev{caret}0`
	introduced earlier is a short-hand for `rev{caret}\{commit\}`.

	* A suffix '{caret}' followed by an empty brace pair
	(e.g. `v0.99.8{caret}\{\}`) means the object could be a tag,
	and dereference the tag recursively until a non-tag object is
	found.

	* A colon, followed by a slash, followed by a text: this names
	a commit whose commit message starts with the specified text.
	This name returns the youngest matching commit which is
	reachable from any ref. If the commit message starts with a
	'!', you have to repeat that; the special sequence ':/!',
	followed by something else than '!' is reserved for now.

	* A suffix ':' followed by a path; this names the blob or tree
	at the given path in the tree-ish object named by the part
	before the colon.

	* A colon, optionally followed by a stage number (0 to 3) and a
	colon, followed by a path; this names a blob object in the
	index at the given path. 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 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 = 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. To these commands,
	specifying a single revision with the notation described in the
	previous section means the set of commits reachable from that
	commit, following the commit ancestry chain.

	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`.

	This 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`.

	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` or `r2` but not from both.

	Two other shorthands for naming a set that is formed by a commit
	and its parent commits exist. The `r1{caret}@` notation means all
	parents of `r1`. `r1{caret}!` includes commit `r1` but excludes
	all of its parents.

	Here are a handful of examples:

	D G H D
	D F G H I J D F
	^G D H D
	^D B E I J F B
	B...C G H D E B C
	^D B C E I J F B C
	C^@ I J F
	F^! D G H D F

	PARSEOPT
	--------

	In `--parseopt` mode, 'git-rev-parse' helps massaging options to bring to shell
	scripts the same facilities C builtins have. It works as an option normalizer
	(e.g. splits single switches aggregate values), a bit like `getopt(1)` does.

	It takes on the standard input the specification of the options to parse and
	understand, and echoes on the standard output a line suitable for `sh(1)` `eval`
	to replace the arguments with normalized ones. In case of error, it outputs
	usage on the standard error stream, and exits with code 129.

	Input Format
	~~~~~~~~~~~~

	'git-rev-parse --parseopt' input format is fully text based. It has two parts,
	separated by a line that contains only `--`. The lines before the separator
	(should be more than one) are used for the usage.
	The lines after the separator describe the options.

	Each line of options has this format:

	------------
	<opt_spec><flags>* SP+ help LF
	------------

	`<opt_spec>`::
	its format is the short option character, then the long option name
	separated by a comma. Both parts are not required, though at least one
	is necessary. `h,help`, `dry-run` and `f` are all three correct
	`<opt_spec>`.

	`<flags>`::
	`<flags>` are of `*`, `=`, `?` or `!`.
	* Use `=` if the option takes an argument.

	* Use `?` to mean that the option is optional (though its use is discouraged).

	* Use `*` to mean that this option should not be listed in the usage
	generated for the `-h` argument. It's shown for `--help-all` as
	documented in linkgit:gitcli[7].

	* Use `!` to not make the corresponding negated long option available.

	The remainder of the line, after stripping the spaces, is used
	as the help associated to the option.

	Blank lines are ignored, and lines that don't match this specification are used
	as option group headers (start the line with a space to create such
	lines on purpose).

	Example
	~~~~~~~

	------------
	OPTS_SPEC="\
	some-command [options] <args>...

	some-command does foo and bar!
	--
	h,help show the help

	foo some nifty option --foo
	bar= some cool option --bar with an argument

	An option group Header
	C? option C with an optional argument"

	eval `echo "$OPTS_SPEC" \| git rev-parse --parseopt -- "$@" \|\| echo exit $?`
	------------

	EXAMPLES
	--------

	* Print the object name of the current commit:
	+
	------------
	$ git rev-parse --verify HEAD
	------------

	* Print the commit object name from the revision in the $REV shell variable:
	+
	------------
	$ git rev-parse --verify $REV
	------------
	+
	This will error out if $REV is empty or not a valid revision.

	* Same as above:
	+
	------------
	$ git rev-parse --default master --verify $REV
	------------
	+
	but if $REV is empty, the commit object name from master will be printed.


	Author
	------
	Written by Linus Torvalds <torvalds@osdl.org> .
	Junio C Hamano <gitster@pobox.com> and Pierre Habouzit <madcoder@debian.org>

	Documentation
	--------------
	Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.

	GIT
	---
	Part of the linkgit:git[1] suite