Documentation/git-interpret-trailers.txt - git - Git at Google

 git-interpret-trailers(1)
 =========================

 NAME
 ----
 git-interpret-trailers - Add or parse structured information in commit messages

 SYNOPSIS
 --------
 [verse]
 'git interpret-trailers' [--in-place] [--trim-empty]
 			[(--trailer (<key>|<key-alias>)[(=|:)<value>])...]
 			[--parse] [<file>...]

 DESCRIPTION
 -----------
 Add or parse 'trailer' lines that look similar to RFC 822 e-mail
 headers, at the end of the otherwise free-form part of a commit
 message. For example, in the following commit message

 ------------------------------------------------
 subject

 Lorem ipsum dolor sit amet, consectetur adipiscing elit.

 Signed-off-by: Alice <alice@example.com>
 Signed-off-by: Bob <bob@example.com>
 ------------------------------------------------

 the last two lines starting with "Signed-off-by" are trailers.

 This command reads commit messages from either the
 <file> arguments or the standard input if no <file> is specified.
 If `--parse` is specified, the output consists of the parsed trailers
 coming from the input, without influencing them with any command line
 options or configuration variables.

 Otherwise, this command applies `trailer.*` configuration variables
 (which could potentially add new trailers, as well as reposition them),
 as well as any command line arguments that can override configuration
 variables (such as `--trailer=...` which could also add new trailers),
 to each input file. The result is emitted on the standard output.

 This command can also operate on the output of linkgit:git-format-patch[1],
 which is more elaborate than a plain commit message. Namely, such output
 includes a commit message (as above), a "---" divider line, and a patch part.
 For these inputs, the divider and patch parts are not modified by
 this command and are emitted as is on the output, unless
 `--no-divider` is specified.

 Some configuration variables control the way the `--trailer` arguments
 are applied to each input and the way any existing trailer in
 the input is changed. They also make it possible to
 automatically add some trailers.

 By default, a '<key>=<value>' or '<key>:<value>' argument given
 using `--trailer` will be appended after the existing trailers only if
 the last trailer has a different (<key>, <value>) pair (or if there
 is no existing trailer). The <key> and <value> parts will be trimmed
 to remove starting and trailing whitespace, and the resulting trimmed
 <key> and <value> will appear in the output like this:

 ------------------------------------------------
 key: value
 ------------------------------------------------

 This means that the trimmed <key> and <value> will be separated by
 `': '` (one colon followed by one space).

 For convenience, a <key-alias> can be configured to make using `--trailer`
 shorter to type on the command line. This can be configured using the
 'trailer.<key-alias>.key' configuration variable. The <keyAlias> must be a prefix
 of the full <key> string, although case sensitivity does not matter. For
 example, if you have

 ------------------------------------------------
 trailer.sign.key "Signed-off-by: "
 ------------------------------------------------

 in your configuration, you only need to specify `--trailer="sign: foo"`
 on the command line instead of `--trailer="Signed-off-by: foo"`.

 By default the new trailer will appear at the end of all the existing
 trailers. If there is no existing trailer, the new trailer will appear
 at the end of the input. A blank line will be added before the new
 trailer if there isn't one already.

 Existing trailers are extracted from the input by looking for
 a group of one or more lines that (i) is all trailers, or (ii) contains at
 least one Git-generated or user-configured trailer and consists of at
 least 25% trailers.
 The group must be preceded by one or more empty (or whitespace-only) lines.
 The group must either be at the end of the input or be the last
 non-whitespace lines before a line that starts with '---' (followed by a
 space or the end of the line).

 When reading trailers, there can be no whitespace before or inside the
 <key>, but any number of regular space and tab characters are allowed
 between the <key> and the separator. There can be whitespaces before,
 inside or after the <value>. The <value> may be split over multiple lines
 with each subsequent line starting with at least one whitespace, like
 the "folding" in RFC 822. Example:

 ------------------------------------------------
 key: This is a very long value, with spaces and
   newlines in it.
 ------------------------------------------------

 Note that trailers do not follow (nor are they intended to follow) many of the
 rules for RFC 822 headers. For example they do not follow the encoding rule.

 OPTIONS
 -------
 --in-place::
 	Edit the files in place.

 --trim-empty::
 	If the <value> part of any trailer contains only whitespace,
 	the whole trailer will be removed from the output.
 	This applies to existing trailers as well as new trailers.

 --trailer <key>[(=|:)<value>]::
 	Specify a (<key>, <value>) pair that should be applied as a
 	trailer to the inputs. See the description of this
 	command.

 --where <placement>::
 --no-where::
 	Specify where all new trailers will be added.  A setting
 	provided with '--where' overrides the `trailer.where` and any
 	applicable `trailer.<keyAlias>.where` configuration variables
 	and applies to all '--trailer' options until the next occurrence of
 	'--where' or '--no-where'. Upon encountering '--no-where', clear the
 	effect of any previous use of '--where', such that the relevant configuration
 	variables are no longer overridden. Possible placements are `after`,
 	`before`, `end` or `start`.

 --if-exists <action>::
 --no-if-exists::
 	Specify what action will be performed when there is already at
 	least one trailer with the same <key> in the input.  A setting
 	provided with '--if-exists' overrides the `trailer.ifExists` and any
 	applicable `trailer.<keyAlias>.ifExists` configuration variables
 	and applies to all '--trailer' options until the next occurrence of
 	'--if-exists' or '--no-if-exists'. Upon encountering '--no-if-exists, clear the
 	effect of any previous use of '--if-exists, such that the relevant configuration
 	variables are no longer overridden. Possible actions are `addIfDifferent`,
 	`addIfDifferentNeighbor`, `add`, `replace` and `doNothing`.

 --if-missing <action>::
 --no-if-missing::
 	Specify what action will be performed when there is no other
 	trailer with the same <key> in the input.  A setting
 	provided with '--if-missing' overrides the `trailer.ifMissing` and any
 	applicable `trailer.<keyAlias>.ifMissing` configuration variables
 	and applies to all '--trailer' options until the next occurrence of
 	'--if-missing' or '--no-if-missing'. Upon encountering '--no-if-missing,
 	clear the effect of any previous use of '--if-missing, such that the relevant
 	configuration variables are no longer overridden. Possible actions are `doNothing`
 	or `add`.

 --only-trailers::
 	Output only the trailers, not any other parts of the input.

 --only-input::
 	Output only trailers that exist in the input; do not add any
 	from the command-line or by applying `trailer.*` configuration
 	variables.

 --unfold::
 	If a trailer has a value that runs over multiple lines (aka "folded"),
 	reformat the value into a single line.

 --parse::
 	A convenience alias for `--only-trailers --only-input
 	--unfold`. This makes it easier to only see the trailers coming from the
 	input without influencing them with any command line options or
 	configuration variables, while also making the output machine-friendly with
 	--unfold.

 --no-divider::
 	Do not treat `---` as the end of the commit message. Use this
 	when you know your input contains just the commit message itself
 	(and not an email or the output of `git format-patch`).

 CONFIGURATION VARIABLES
 -----------------------

 trailer.separators::
 	This option tells which characters are recognized as trailer
 	separators. By default only ':' is recognized as a trailer
 	separator, except that '=' is always accepted on the command
 	line for compatibility with other git commands.
 +
 The first character given by this option will be the default character
 used when another separator is not specified in the config for this
 trailer.
 +
 For example, if the value for this option is "%=$", then only lines
 using the format '<key><sep><value>' with <sep> containing '%', '='
 or '$' and then spaces will be considered trailers. And '%' will be
 the default separator used, so by default trailers will appear like:
 '<key>% <value>' (one percent sign and one space will appear between
 the key and the value).

 trailer.where::
 	This option tells where a new trailer will be added.
 +
 This can be `end`, which is the default, `start`, `after` or `before`.
 +
 If it is `end`, then each new trailer will appear at the end of the
 existing trailers.
 +
 If it is `start`, then each new trailer will appear at the start,
 instead of the end, of the existing trailers.
 +
 If it is `after`, then each new trailer will appear just after the
 last trailer with the same <key>.
 +
 If it is `before`, then each new trailer will appear just before the
 first trailer with the same <key>.

 trailer.ifexists::
 	This option makes it possible to choose what action will be
 	performed when there is already at least one trailer with the
 	same <key> in the input.
 +
 The valid values for this option are: `addIfDifferentNeighbor` (this
 is the default), `addIfDifferent`, `add`, `replace` or `doNothing`.
 +
 With `addIfDifferentNeighbor`, a new trailer will be added only if no
 trailer with the same (<key>, <value>) pair is above or below the line
 where the new trailer will be added.
 +
 With `addIfDifferent`, a new trailer will be added only if no trailer
 with the same (<key>, <value>) pair is already in the input.
 +
 With `add`, a new trailer will be added, even if some trailers with
 the same (<key>, <value>) pair are already in the input.
 +
 With `replace`, an existing trailer with the same <key> will be
 deleted and the new trailer will be added. The deleted trailer will be
 the closest one (with the same <key>) to the place where the new one
 will be added.
 +
 With `doNothing`, nothing will be done; that is no new trailer will be
 added if there is already one with the same <key> in the input.

 trailer.ifmissing::
 	This option makes it possible to choose what action will be
 	performed when there is not yet any trailer with the same
 	<key> in the input.
 +
 The valid values for this option are: `add` (this is the default) and
 `doNothing`.
 +
 With `add`, a new trailer will be added.
 +
 With `doNothing`, nothing will be done.

 trailer.<keyAlias>.key::
 	Defines a <keyAlias> for the <key>. The <keyAlias> must be a
 	prefix (case does not matter) of the <key>. For example, in `git
 	config trailer.ack.key "Acked-by"` the "Acked-by" is the <key> and
 	the "ack" is the <keyAlias>. This configuration allows the shorter
 	`--trailer "ack:..."` invocation on the command line using the "ack"
 	<keyAlias> instead of the longer `--trailer "Acked-by:..."`.
 +
 At the end of the <key>, a separator can appear and then some
 space characters. By default the only valid separator is ':',
 but this can be changed using the `trailer.separators` config
 variable.
 +
 If there is a separator in the key, then it overrides the default
 separator when adding the trailer.

 trailer.<keyAlias>.where::
 	This option takes the same values as the 'trailer.where'
 	configuration variable and it overrides what is specified by
 	that option for trailers with the specified <keyAlias>.

 trailer.<keyAlias>.ifexists::
 	This option takes the same values as the 'trailer.ifexists'
 	configuration variable and it overrides what is specified by
 	that option for trailers with the specified <keyAlias>.

 trailer.<keyAlias>.ifmissing::
 	This option takes the same values as the 'trailer.ifmissing'
 	configuration variable and it overrides what is specified by
 	that option for trailers with the specified <keyAlias>.

 trailer.<keyAlias>.command::
 	Deprecated in favor of 'trailer.<keyAlias>.cmd'.
 	This option behaves in the same way as 'trailer.<keyAlias>.cmd', except
 	that it doesn't pass anything as argument to the specified command.
 	Instead the first occurrence of substring $ARG is replaced by the
 	<value> that would be passed as argument.
 +
 Note that $ARG in the user's command is
 only replaced once and that the original way of replacing $ARG is not safe.
 +
 When both 'trailer.<keyAlias>.cmd' and 'trailer.<keyAlias>.command' are given
 for the same <keyAlias>, 'trailer.<keyAlias>.cmd' is used and
 'trailer.<keyAlias>.command' is ignored.

 trailer.<keyAlias>.cmd::
 	This option can be used to specify a shell command that will be called
 	once to automatically add a trailer with the specified <keyAlias>, and then
 	called each time a '--trailer <keyAlias>=<value>' argument is specified to
 	modify the <value> of the trailer that this option would produce.
 +
 When the specified command is first called to add a trailer
 with the specified <keyAlias>, the behavior is as if a special
 '--trailer <keyAlias>=<value>' argument was added at the beginning
 of the "git interpret-trailers" command, where <value>
 is taken to be the standard output of the command with any
 leading and trailing whitespace trimmed off.
 +
 If some '--trailer <keyAlias>=<value>' arguments are also passed
 on the command line, the command is called again once for each
 of these arguments with the same <keyAlias>. And the <value> part
 of these arguments, if any, will be passed to the command as its
 first argument. This way the command can produce a <value> computed
 from the <value> passed in the '--trailer <keyAlias>=<value>' argument.

 EXAMPLES
 --------

 * Configure a 'sign' trailer with a 'Signed-off-by' key, and then
   add two of these trailers to a commit message file:
 +
 ------------
 $ git config trailer.sign.key "Signed-off-by"
 $ cat msg.txt
 subject

 body text
 $ git interpret-trailers --trailer 'sign: Alice <alice@example.com>' --trailer 'sign: Bob <bob@example.com>' <msg.txt
 subject

 body text

 Signed-off-by: Alice <alice@example.com>
 Signed-off-by: Bob <bob@example.com>
 ------------

 * Use the `--in-place` option to edit a commit message file in place:
 +
 ------------
 $ cat msg.txt
 subject

 body text

 Signed-off-by: Bob <bob@example.com>
 $ git interpret-trailers --trailer 'Acked-by: Alice <alice@example.com>' --in-place msg.txt
 $ cat msg.txt
 subject

 body text

 Signed-off-by: Bob <bob@example.com>
 Acked-by: Alice <alice@example.com>
 ------------

 * Extract the last commit as a patch, and add a 'Cc' and a
   'Reviewed-by' trailer to it:
 +
 ------------
 $ git format-patch -1
 0001-foo.patch
 $ git interpret-trailers --trailer 'Cc: Alice <alice@example.com>' --trailer 'Reviewed-by: Bob <bob@example.com>' 0001-foo.patch >0001-bar.patch
 ------------

 * Configure a 'sign' trailer with a command to automatically add a
   'Signed-off-by: ' with the author information only if there is no
   'Signed-off-by: ' already, and show how it works:
 +
 ------------
 $ cat msg1.txt
 subject

 body text
 $ git config trailer.sign.key "Signed-off-by: "
 $ git config trailer.sign.ifmissing add
 $ git config trailer.sign.ifexists doNothing
 $ git config trailer.sign.cmd 'echo "$(git config user.name) <$(git config user.email)>"'
 $ git interpret-trailers --trailer sign <msg1.txt
 subject

 body text

 Signed-off-by: Bob <bob@example.com>
 $ cat msg2.txt
 subject

 body text

 Signed-off-by: Alice <alice@example.com>
 $ git interpret-trailers --trailer sign <msg2.txt
 subject

 body text

 Signed-off-by: Alice <alice@example.com>
 ------------

 * Configure a 'fix' trailer with a key that contains a '#' and no
   space after this character, and show how it works:
 +
 ------------
 $ git config trailer.separators ":#"
 $ git config trailer.fix.key "Fix #"
 $ echo "subject" | git interpret-trailers --trailer fix=42
 subject

 Fix #42
 ------------

 * Configure a 'help' trailer with a cmd use a script `glog-find-author`
   which search specified author identity from git log in git repository
   and show how it works:
 +
 ------------
 $ cat ~/bin/glog-find-author
 #!/bin/sh
 test -n "$1" && git log --author="$1" --pretty="%an <%ae>" -1 || true
 $ cat msg.txt
 subject

 body text
 $ git config trailer.help.key "Helped-by: "
 $ git config trailer.help.ifExists "addIfDifferentNeighbor"
 $ git config trailer.help.cmd "~/bin/glog-find-author"
 $ git interpret-trailers --trailer="help:Junio" --trailer="help:Couder" <msg.txt
 subject

 body text

 Helped-by: Junio C Hamano <gitster@pobox.com>
 Helped-by: Christian Couder <christian.couder@gmail.com>
 ------------

 * Configure a 'ref' trailer with a cmd use a script `glog-grep`
   to grep last relevant commit from git log in the git repository
   and show how it works:
 +
 ------------
 $ cat ~/bin/glog-grep
 #!/bin/sh
 test -n "$1" && git log --grep "$1" --pretty=reference -1 || true
 $ cat msg.txt
 subject

 body text
 $ git config trailer.ref.key "Reference-to: "
 $ git config trailer.ref.ifExists "replace"
 $ git config trailer.ref.cmd "~/bin/glog-grep"
 $ git interpret-trailers --trailer="ref:Add copyright notices." <msg.txt
 subject

 body text

 Reference-to: 8bc9a0c769 (Add copyright notices., 2005-04-07)
 ------------

 * Configure a 'see' trailer with a command to show the subject of a
   commit that is related, and show how it works:
 +
 ------------
 $ cat msg.txt
 subject

 body text

 see: HEAD~2
 $ cat ~/bin/glog-ref
 #!/bin/sh
 git log -1 --oneline --format="%h (%s)" --abbrev-commit --abbrev=14
 $ git config trailer.see.key "See-also: "
 $ git config trailer.see.ifExists "replace"
 $ git config trailer.see.ifMissing "doNothing"
 $ git config trailer.see.cmd "glog-ref"
 $ git interpret-trailers --trailer=see <msg.txt
 subject

 body text

 See-also: fe3187489d69c4 (subject of related commit)
 ------------

 * Configure a commit template with some trailers with empty values
   (using sed to show and keep the trailing spaces at the end of the
   trailers), then configure a commit-msg hook that uses
   'git interpret-trailers' to remove trailers with empty values and
   to add a 'git-version' trailer:
 +
 ------------
 $ cat temp.txt
 ***subject***

 ***message***

 Fixes: Z
 Cc: Z
 Reviewed-by: Z
 Signed-off-by: Z
 $ sed -e 's/ Z$/ /' temp.txt > commit_template.txt
 $ git config commit.template commit_template.txt
 $ cat .git/hooks/commit-msg
 #!/bin/sh
 git interpret-trailers --trim-empty --trailer "git-version: \$(git describe)" "\$1" > "\$1.new"
 mv "\$1.new" "\$1"
 $ chmod +x .git/hooks/commit-msg
 ------------

 SEE ALSO
 --------
 linkgit:git-commit[1], linkgit:git-format-patch[1], linkgit:git-config[1]

 GIT
 ---
 Part of the linkgit:git[1] suite
	git-interpret-trailers(1)
	=========================

	NAME
	----
	git-interpret-trailers - Add or parse structured information in commit messages

	SYNOPSIS
	--------
	[verse]
	'git interpret-trailers' [--in-place] [--trim-empty]
	[(--trailer (<key>\|<key-alias>)[(=\|:)<value>])...]
	[--parse] [<file>...]

	DESCRIPTION
	-----------
	Add or parse 'trailer' lines that look similar to RFC 822 e-mail
	headers, at the end of the otherwise free-form part of a commit
	message. For example, in the following commit message

	------------------------------------------------
	subject

	Lorem ipsum dolor sit amet, consectetur adipiscing elit.

	Signed-off-by: Alice <alice@example.com>
	Signed-off-by: Bob <bob@example.com>
	------------------------------------------------

	the last two lines starting with "Signed-off-by" are trailers.

	This command reads commit messages from either the
	<file> arguments or the standard input if no <file> is specified.
	If `--parse` is specified, the output consists of the parsed trailers
	coming from the input, without influencing them with any command line
	options or configuration variables.

	Otherwise, this command applies `trailer.*` configuration variables
	(which could potentially add new trailers, as well as reposition them),
	as well as any command line arguments that can override configuration
	variables (such as `--trailer=...` which could also add new trailers),
	to each input file. The result is emitted on the standard output.

	This command can also operate on the output of linkgit:git-format-patch[1],
	which is more elaborate than a plain commit message. Namely, such output
	includes a commit message (as above), a "---" divider line, and a patch part.
	For these inputs, the divider and patch parts are not modified by
	this command and are emitted as is on the output, unless
	`--no-divider` is specified.

	Some configuration variables control the way the `--trailer` arguments
	are applied to each input and the way any existing trailer in
	the input is changed. They also make it possible to
	automatically add some trailers.

	By default, a '<key>=<value>' or '<key>:<value>' argument given
	using `--trailer` will be appended after the existing trailers only if
	the last trailer has a different (<key>, <value>) pair (or if there
	is no existing trailer). The <key> and <value> parts will be trimmed
	to remove starting and trailing whitespace, and the resulting trimmed
	<key> and <value> will appear in the output like this:

	------------------------------------------------
	key: value
	------------------------------------------------

	This means that the trimmed <key> and <value> will be separated by
	`': '` (one colon followed by one space).

	For convenience, a <key-alias> can be configured to make using `--trailer`
	shorter to type on the command line. This can be configured using the
	'trailer.<key-alias>.key' configuration variable. The <keyAlias> must be a prefix
	of the full <key> string, although case sensitivity does not matter. For
	example, if you have

	------------------------------------------------
	trailer.sign.key "Signed-off-by: "
	------------------------------------------------

	in your configuration, you only need to specify `--trailer="sign: foo"`
	on the command line instead of `--trailer="Signed-off-by: foo"`.

	By default the new trailer will appear at the end of all the existing
	trailers. If there is no existing trailer, the new trailer will appear
	at the end of the input. A blank line will be added before the new
	trailer if there isn't one already.

	Existing trailers are extracted from the input by looking for
	a group of one or more lines that (i) is all trailers, or (ii) contains at
	least one Git-generated or user-configured trailer and consists of at
	least 25% trailers.
	The group must be preceded by one or more empty (or whitespace-only) lines.
	The group must either be at the end of the input or be the last
	non-whitespace lines before a line that starts with '---' (followed by a
	space or the end of the line).

	When reading trailers, there can be no whitespace before or inside the
	<key>, but any number of regular space and tab characters are allowed
	between the <key> and the separator. There can be whitespaces before,
	inside or after the <value>. The <value> may be split over multiple lines
	with each subsequent line starting with at least one whitespace, like
	the "folding" in RFC 822. Example:

	------------------------------------------------
	key: This is a very long value, with spaces and
	newlines in it.
	------------------------------------------------

	Note that trailers do not follow (nor are they intended to follow) many of the
	rules for RFC 822 headers. For example they do not follow the encoding rule.

	OPTIONS
	-------
	--in-place::
	Edit the files in place.

	--trim-empty::
	If the <value> part of any trailer contains only whitespace,
	the whole trailer will be removed from the output.
	This applies to existing trailers as well as new trailers.

	--trailer <key>[(=\|:)<value>]::
	Specify a (<key>, <value>) pair that should be applied as a
	trailer to the inputs. See the description of this
	command.

	--where <placement>::
	--no-where::
	Specify where all new trailers will be added. A setting
	provided with '--where' overrides the `trailer.where` and any
	applicable `trailer.<keyAlias>.where` configuration variables
	and applies to all '--trailer' options until the next occurrence of
	'--where' or '--no-where'. Upon encountering '--no-where', clear the
	effect of any previous use of '--where', such that the relevant configuration
	variables are no longer overridden. Possible placements are `after`,
	`before`, `end` or `start`.

	--if-exists <action>::
	--no-if-exists::
	Specify what action will be performed when there is already at
	least one trailer with the same <key> in the input. A setting
	provided with '--if-exists' overrides the `trailer.ifExists` and any
	applicable `trailer.<keyAlias>.ifExists` configuration variables
	and applies to all '--trailer' options until the next occurrence of
	'--if-exists' or '--no-if-exists'. Upon encountering '--no-if-exists, clear the
	effect of any previous use of '--if-exists, such that the relevant configuration
	variables are no longer overridden. Possible actions are `addIfDifferent`,
	`addIfDifferentNeighbor`, `add`, `replace` and `doNothing`.

	--if-missing <action>::
	--no-if-missing::
	Specify what action will be performed when there is no other
	trailer with the same <key> in the input. A setting
	provided with '--if-missing' overrides the `trailer.ifMissing` and any
	applicable `trailer.<keyAlias>.ifMissing` configuration variables
	and applies to all '--trailer' options until the next occurrence of
	'--if-missing' or '--no-if-missing'. Upon encountering '--no-if-missing,
	clear the effect of any previous use of '--if-missing, such that the relevant
	configuration variables are no longer overridden. Possible actions are `doNothing`
	or `add`.

	--only-trailers::
	Output only the trailers, not any other parts of the input.

	--only-input::
	Output only trailers that exist in the input; do not add any
	from the command-line or by applying `trailer.*` configuration
	variables.

	--unfold::
	If a trailer has a value that runs over multiple lines (aka "folded"),
	reformat the value into a single line.

	--parse::
	A convenience alias for `--only-trailers --only-input
	--unfold`. This makes it easier to only see the trailers coming from the
	input without influencing them with any command line options or
	configuration variables, while also making the output machine-friendly with
	--unfold.

	--no-divider::
	Do not treat `---` as the end of the commit message. Use this
	when you know your input contains just the commit message itself
	(and not an email or the output of `git format-patch`).

	CONFIGURATION VARIABLES
	-----------------------

	trailer.separators::
	This option tells which characters are recognized as trailer
	separators. By default only ':' is recognized as a trailer
	separator, except that '=' is always accepted on the command
	line for compatibility with other git commands.
	+
	The first character given by this option will be the default character
	used when another separator is not specified in the config for this
	trailer.
	+
	For example, if the value for this option is "%=$", then only lines
	using the format '<key><sep><value>' with <sep> containing '%', '='
	or '$' and then spaces will be considered trailers. And '%' will be
	the default separator used, so by default trailers will appear like:
	'<key>% <value>' (one percent sign and one space will appear between
	the key and the value).

	trailer.where::
	This option tells where a new trailer will be added.
	+
	This can be `end`, which is the default, `start`, `after` or `before`.
	+
	If it is `end`, then each new trailer will appear at the end of the
	existing trailers.
	+
	If it is `start`, then each new trailer will appear at the start,
	instead of the end, of the existing trailers.
	+
	If it is `after`, then each new trailer will appear just after the
	last trailer with the same <key>.
	+
	If it is `before`, then each new trailer will appear just before the
	first trailer with the same <key>.

	trailer.ifexists::
	This option makes it possible to choose what action will be
	performed when there is already at least one trailer with the
	same <key> in the input.
	+
	The valid values for this option are: `addIfDifferentNeighbor` (this
	is the default), `addIfDifferent`, `add`, `replace` or `doNothing`.
	+
	With `addIfDifferentNeighbor`, a new trailer will be added only if no
	trailer with the same (<key>, <value>) pair is above or below the line
	where the new trailer will be added.
	+
	With `addIfDifferent`, a new trailer will be added only if no trailer
	with the same (<key>, <value>) pair is already in the input.
	+
	With `add`, a new trailer will be added, even if some trailers with
	the same (<key>, <value>) pair are already in the input.
	+
	With `replace`, an existing trailer with the same <key> will be
	deleted and the new trailer will be added. The deleted trailer will be
	the closest one (with the same <key>) to the place where the new one
	will be added.
	+
	With `doNothing`, nothing will be done; that is no new trailer will be
	added if there is already one with the same <key> in the input.

	trailer.ifmissing::
	This option makes it possible to choose what action will be
	performed when there is not yet any trailer with the same
	<key> in the input.
	+
	The valid values for this option are: `add` (this is the default) and
	`doNothing`.
	+
	With `add`, a new trailer will be added.
	+
	With `doNothing`, nothing will be done.

	trailer.<keyAlias>.key::
	Defines a <keyAlias> for the <key>. The <keyAlias> must be a
	prefix (case does not matter) of the <key>. For example, in `git
	config trailer.ack.key "Acked-by"` the "Acked-by" is the <key> and
	the "ack" is the <keyAlias>. This configuration allows the shorter
	`--trailer "ack:..."` invocation on the command line using the "ack"
	<keyAlias> instead of the longer `--trailer "Acked-by:..."`.
	+
	At the end of the <key>, a separator can appear and then some
	space characters. By default the only valid separator is ':',
	but this can be changed using the `trailer.separators` config
	variable.
	+
	If there is a separator in the key, then it overrides the default
	separator when adding the trailer.

	trailer.<keyAlias>.where::
	This option takes the same values as the 'trailer.where'
	configuration variable and it overrides what is specified by
	that option for trailers with the specified <keyAlias>.

	trailer.<keyAlias>.ifexists::
	This option takes the same values as the 'trailer.ifexists'
	configuration variable and it overrides what is specified by
	that option for trailers with the specified <keyAlias>.

	trailer.<keyAlias>.ifmissing::
	This option takes the same values as the 'trailer.ifmissing'
	configuration variable and it overrides what is specified by
	that option for trailers with the specified <keyAlias>.

	trailer.<keyAlias>.command::
	Deprecated in favor of 'trailer.<keyAlias>.cmd'.
	This option behaves in the same way as 'trailer.<keyAlias>.cmd', except
	that it doesn't pass anything as argument to the specified command.
	Instead the first occurrence of substring $ARG is replaced by the
	<value> that would be passed as argument.
	+
	Note that $ARG in the user's command is
	only replaced once and that the original way of replacing $ARG is not safe.
	+
	When both 'trailer.<keyAlias>.cmd' and 'trailer.<keyAlias>.command' are given
	for the same <keyAlias>, 'trailer.<keyAlias>.cmd' is used and
	'trailer.<keyAlias>.command' is ignored.

	trailer.<keyAlias>.cmd::
	This option can be used to specify a shell command that will be called
	once to automatically add a trailer with the specified <keyAlias>, and then
	called each time a '--trailer <keyAlias>=<value>' argument is specified to
	modify the <value> of the trailer that this option would produce.
	+
	When the specified command is first called to add a trailer
	with the specified <keyAlias>, the behavior is as if a special
	'--trailer <keyAlias>=<value>' argument was added at the beginning
	of the "git interpret-trailers" command, where <value>
	is taken to be the standard output of the command with any
	leading and trailing whitespace trimmed off.
	+
	If some '--trailer <keyAlias>=<value>' arguments are also passed
	on the command line, the command is called again once for each
	of these arguments with the same <keyAlias>. And the <value> part
	of these arguments, if any, will be passed to the command as its
	first argument. This way the command can produce a <value> computed
	from the <value> passed in the '--trailer <keyAlias>=<value>' argument.

	EXAMPLES
	--------

	* Configure a 'sign' trailer with a 'Signed-off-by' key, and then
	add two of these trailers to a commit message file:
	+
	------------
	$ git config trailer.sign.key "Signed-off-by"
	$ cat msg.txt
	subject

	body text
	$ git interpret-trailers --trailer 'sign: Alice <alice@example.com>' --trailer 'sign: Bob <bob@example.com>' <msg.txt
	subject

	body text

	Signed-off-by: Alice <alice@example.com>
	Signed-off-by: Bob <bob@example.com>
	------------

	* Use the `--in-place` option to edit a commit message file in place:
	+
	------------
	$ cat msg.txt
	subject

	body text

	Signed-off-by: Bob <bob@example.com>
	$ git interpret-trailers --trailer 'Acked-by: Alice <alice@example.com>' --in-place msg.txt
	$ cat msg.txt
	subject

	body text

	Signed-off-by: Bob <bob@example.com>
	Acked-by: Alice <alice@example.com>
	------------

	* Extract the last commit as a patch, and add a 'Cc' and a
	'Reviewed-by' trailer to it:
	+
	------------
	$ git format-patch -1
	0001-foo.patch
	$ git interpret-trailers --trailer 'Cc: Alice <alice@example.com>' --trailer 'Reviewed-by: Bob <bob@example.com>' 0001-foo.patch >0001-bar.patch
	------------

	* Configure a 'sign' trailer with a command to automatically add a
	'Signed-off-by: ' with the author information only if there is no
	'Signed-off-by: ' already, and show how it works:
	+
	------------
	$ cat msg1.txt
	subject

	body text
	$ git config trailer.sign.key "Signed-off-by: "
	$ git config trailer.sign.ifmissing add
	$ git config trailer.sign.ifexists doNothing
	$ git config trailer.sign.cmd 'echo "$(git config user.name) <$(git config user.email)>"'
	$ git interpret-trailers --trailer sign <msg1.txt
	subject

	body text

	Signed-off-by: Bob <bob@example.com>
	$ cat msg2.txt
	subject

	body text

	Signed-off-by: Alice <alice@example.com>
	$ git interpret-trailers --trailer sign <msg2.txt
	subject

	body text

	Signed-off-by: Alice <alice@example.com>
	------------

	* Configure a 'fix' trailer with a key that contains a '#' and no
	space after this character, and show how it works:
	+
	------------
	$ git config trailer.separators ":#"
	$ git config trailer.fix.key "Fix #"
	$ echo "subject" \| git interpret-trailers --trailer fix=42
	subject

	Fix #42
	------------

	* Configure a 'help' trailer with a cmd use a script `glog-find-author`
	which search specified author identity from git log in git repository
	and show how it works:
	+
	------------
	$ cat ~/bin/glog-find-author
	#!/bin/sh
	test -n "$1" && git log --author="$1" --pretty="%an <%ae>" -1 \|\| true
	$ cat msg.txt
	subject

	body text
	$ git config trailer.help.key "Helped-by: "
	$ git config trailer.help.ifExists "addIfDifferentNeighbor"
	$ git config trailer.help.cmd "~/bin/glog-find-author"
	$ git interpret-trailers --trailer="help:Junio" --trailer="help:Couder" <msg.txt
	subject

	body text

	Helped-by: Junio C Hamano <gitster@pobox.com>
	Helped-by: Christian Couder <christian.couder@gmail.com>
	------------

	* Configure a 'ref' trailer with a cmd use a script `glog-grep`
	to grep last relevant commit from git log in the git repository
	and show how it works:
	+
	------------
	$ cat ~/bin/glog-grep
	#!/bin/sh
	test -n "$1" && git log --grep "$1" --pretty=reference -1 \|\| true
	$ cat msg.txt
	subject

	body text
	$ git config trailer.ref.key "Reference-to: "
	$ git config trailer.ref.ifExists "replace"
	$ git config trailer.ref.cmd "~/bin/glog-grep"
	$ git interpret-trailers --trailer="ref:Add copyright notices." <msg.txt
	subject

	body text

	Reference-to: 8bc9a0c769 (Add copyright notices., 2005-04-07)
	------------

	* Configure a 'see' trailer with a command to show the subject of a
	commit that is related, and show how it works:
	+
	------------
	$ cat msg.txt
	subject

	body text

	see: HEAD~2
	$ cat ~/bin/glog-ref
	#!/bin/sh
	git log -1 --oneline --format="%h (%s)" --abbrev-commit --abbrev=14
	$ git config trailer.see.key "See-also: "
	$ git config trailer.see.ifExists "replace"
	$ git config trailer.see.ifMissing "doNothing"
	$ git config trailer.see.cmd "glog-ref"
	$ git interpret-trailers --trailer=see <msg.txt
	subject

	body text

	See-also: fe3187489d69c4 (subject of related commit)
	------------

	* Configure a commit template with some trailers with empty values
	(using sed to show and keep the trailing spaces at the end of the
	trailers), then configure a commit-msg hook that uses
	'git interpret-trailers' to remove trailers with empty values and
	to add a 'git-version' trailer:
	+
	------------
	$ cat temp.txt
	*subject*

	*message*

	Fixes: Z
	Cc: Z
	Reviewed-by: Z
	Signed-off-by: Z
	$ sed -e 's/ Z$/ /' temp.txt > commit_template.txt
	$ git config commit.template commit_template.txt
	$ cat .git/hooks/commit-msg
	#!/bin/sh
	git interpret-trailers --trim-empty --trailer "git-version: \$(git describe)" "\$1" > "\$1.new"
	mv "\$1.new" "\$1"
	$ chmod +x .git/hooks/commit-msg
	------------

	SEE ALSO
	--------
	linkgit:git-commit[1], linkgit:git-format-patch[1], linkgit:git-config[1]

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