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' [<options>] [(--trailer <token>[(=|:)<value>])...] [<file>...]

            
            'git interpret-trailers' [<options>] [--parse] [<file>...]


            DESCRIPTION

            
            -----------

            
            Help parsing or adding 'trailers' lines, that look similar to RFC 822 e-mail

            
            headers, at the end of the otherwise free-form part of a commit

            
            message.


            This command reads some patches or 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.


            Otherwise, this command applies the arguments passed using the

            
            `--trailer` option, if any, to the commit message part of each input

            
            file. The result is emitted on the standard output.


            Some configuration variables control the way the `--trailer` arguments

            
            are applied to each commit message and the way any existing trailer in

            
            the commit message is changed. They also make it possible to

            
            automatically add some trailers.


            By default, a '<token>=<value>' or '<token>:<value>' argument given

            
            using `--trailer` will be appended after the existing trailers only if

            
            the last trailer has a different (<token>, <value>) pair (or if there

            
            is no existing trailer). The <token> and <value> parts will be trimmed

            
            to remove starting and trailing whitespace, and the resulting trimmed

            
            <token> and <value> will appear in the message like this:


            ------------------------------------------------

            
            token: value

            
            ------------------------------------------------


            This means that the trimmed <token> and <value> will be separated by

            
            `': '` (one colon followed by one space).


            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

            
            after the commit message part of the output, and, if there is no line

            
            with only spaces at the end of the commit message part, one blank line

            
            will be added before the new trailer.


            Existing trailers are extracted from the input message 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 message or be the last

            
            non-whitespace lines before a line that starts with '---' (followed by a

            
            space or the end of the line). Such three minus signs start the patch

            
            part of the message. See also `--no-divider` below.


            When reading trailers, there can be whitespaces after the

            
            token, the separator and the value. There can also be whitespaces

            
            inside the token and the value. The value may be split over multiple lines with

            
            each subsequent line starting with whitespace, like the "folding" in RFC 822.


            Note that 'trailers' do not follow and are not intended to follow many

            
            rules for RFC 822 headers. For example they do not follow

            
            the encoding rules and probably many other rules.


            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 resulting message.

            
            	This applies to existing trailers as well as new trailers.


            --trailer <token>[(=|:)<value>]::

            
            	Specify a (<token>, <value>) pair that should be applied as a

            
            	trailer to the input messages. See the description of this

            
            	command.


            --where <placement>::

            
            --no-where::

            
            	Specify where all new trailers will be added.  A setting

            
            	provided with '--where' overrides all configuration variables

            
            	and applies to all '--trailer' options until the next occurrence of

            
            	'--where' or '--no-where'. Possible values 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 <token> in the message.  A setting

            
            	provided with '--if-exists' overrides all configuration variables

            
            	and applies to all '--trailer' options until the next occurrence of

            
            	'--if-exists' or '--no-if-exists'. 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 <token> in the message.  A setting

            
            	provided with '--if-missing' overrides all configuration variables

            
            	and applies to all '--trailer' options until the next occurrence of

            
            	'--if-missing' or '--no-if-missing'. 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 following configured `trailer.*`

            
            	rules.


            --unfold::

            
            	Remove any whitespace-continuation in trailers, so that each

            
            	trailer appears on a line by itself with its full content.


            --parse::

            
            	A convenience alias for `--only-trailers --only-input

            
            	--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 '<token><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:

            
            '<token>% <value>' (one percent sign and one space will appear between

            
            the token 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 <token>.

            
            +

            
            If it is `before`, then each new trailer will appear just before the

            
            first trailer with the same <token>.


            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 <token> in the message.

            
            +

            
            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 (<token>, <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 (<token>, <value>) pair is already in the message.

            
            +

            
            With `add`, a new trailer will be added, even if some trailers with

            
            the same (<token>, <value>) pair are already in the message.

            
            +

            
            With `replace`, an existing trailer with the same <token> will be

            
            deleted and the new trailer will be added. The deleted trailer will be

            
            the closest one (with the same <token>) 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 <token> in the message.


            trailer.ifmissing::

            
            	This option makes it possible to choose what action will be

            
            	performed when there is not yet any trailer with the same

            
            	<token> in the message.

            
            +

            
            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.<token>.key::

            
            	This `key` will be used instead of <token> in the trailer. At

            
            	the end of this 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, then the key will be used instead of both the

            
            <token> and the default separator when adding the trailer.


            trailer.<token>.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 <token>.


            trailer.<token>.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 <token>.


            trailer.<token>.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 <token>.


            trailer.<token>.command::

            
            	This option can be used to specify a shell command that will

            
            	be called to automatically add or modify a trailer with the

            
            	specified <token>.

            
            +

            
            When this option is specified, the behavior is as if a special

            
            '<token>=<value>' argument were added at the beginning of the command

            
            line, where <value> is taken to be the standard output of the

            
            specified command with any leading and trailing whitespace trimmed

            
            off.

            
            +

            
            If the command contains the `$ARG` string, this string will be

            
            replaced with the <value> part of an existing trailer with the same

            
            <token>, if any, before the command is launched.

            
            +

            
            If some '<token>=<value>' arguments are also passed on the command

            
            line, when a 'trailer.<token>.command' is configured, the command will

            
            also be executed for each of these arguments. And the <value> part of

            
            these arguments, if any, will be used to replace the `$ARG` string in

            
            the command.


            EXAMPLES

            
            --------


            * Configure a 'sign' trailer with a 'Signed-off-by' key, and then

            
              add two of these trailers to a message:

            
            +

            
            ------------

            
            $ git config trailer.sign.key "Signed-off-by"

            
            $ cat msg.txt

            
            subject


            message

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

            
            subject


            message


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

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

            
            ------------


            * Use the `--in-place` option to edit a message file in place:

            
            +

            
            ------------

            
            $ cat msg.txt

            
            subject


            message


            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


            message


            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:

            
            +

            
            ------------

            
            $ git config trailer.sign.key "Signed-off-by: "

            
            $ git config trailer.sign.ifmissing add

            
            $ git config trailer.sign.ifexists doNothing

            
            $ git config trailer.sign.command 'echo "$(git config user.name) <$(git config user.email)>"'

            
            $ git interpret-trailers <<EOF

            
            > EOF


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

            
            $ git interpret-trailers <<EOF

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

            
            > EOF


            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 'see' trailer with a command to show the subject of a

            
              commit that is related, and show how it works:

            
            +

            
            ------------

            
            $ git config trailer.see.key "See-also: "

            
            $ git config trailer.see.ifExists "replace"

            
            $ git config trailer.see.ifMissing "doNothing"

            
            $ git config trailer.see.command "git log -1 --oneline --format=\"%h (%s)\" --abbrev-commit --abbrev=14 \$ARG"

            
            $ git interpret-trailers <<EOF

            
            > subject

            
            >

            
            > message

            
            >

            
            > see: HEAD~2

            
            > EOF

            
            subject


            message


            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:

            
            +

            
            ------------

            
            $ sed -e 's/ Z$/ /' >commit_template.txt <<EOF

            
            > ***subject***

            
            >

            
            > ***message***

            
            >

            
            > Fixes: Z

            
            > Cc: Z

            
            > Reviewed-by: Z

            
            > Signed-off-by: Z

            
            > EOF

            
            $ git config commit.template commit_template.txt

            
            $ cat >.git/hooks/commit-msg <<EOF

            
            > #!/bin/sh

            
            > git interpret-trailers --trim-empty --trailer "git-version: \$(git describe)" "\$1" > "\$1.new"

            
            > mv "\$1.new" "\$1"

            
            > EOF

            
            $ 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' [<options>] [(--trailer <token>[(=\|:)<value>])...] [<file>...]
	'git interpret-trailers' [<options>] [--parse] [<file>...]

	DESCRIPTION
	-----------
	Help parsing or adding 'trailers' lines, that look similar to RFC 822 e-mail
	headers, at the end of the otherwise free-form part of a commit
	message.

	This command reads some patches or 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.

	Otherwise, this command applies the arguments passed using the
	`--trailer` option, if any, to the commit message part of each input
	file. The result is emitted on the standard output.

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

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

	------------------------------------------------
	token: value
	------------------------------------------------

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

	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
	after the commit message part of the output, and, if there is no line
	with only spaces at the end of the commit message part, one blank line
	will be added before the new trailer.

	Existing trailers are extracted from the input message 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 message or be the last
	non-whitespace lines before a line that starts with '---' (followed by a
	space or the end of the line). Such three minus signs start the patch
	part of the message. See also `--no-divider` below.

	When reading trailers, there can be whitespaces after the
	token, the separator and the value. There can also be whitespaces
	inside the token and the value. The value may be split over multiple lines with
	each subsequent line starting with whitespace, like the "folding" in RFC 822.

	Note that 'trailers' do not follow and are not intended to follow many
	rules for RFC 822 headers. For example they do not follow
	the encoding rules and probably many other rules.

	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 resulting message.
	This applies to existing trailers as well as new trailers.

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

	--where <placement>::
	--no-where::
	Specify where all new trailers will be added. A setting
	provided with '--where' overrides all configuration variables
	and applies to all '--trailer' options until the next occurrence of
	'--where' or '--no-where'. Possible values 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 <token> in the message. A setting
	provided with '--if-exists' overrides all configuration variables
	and applies to all '--trailer' options until the next occurrence of
	'--if-exists' or '--no-if-exists'. 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 <token> in the message. A setting
	provided with '--if-missing' overrides all configuration variables
	and applies to all '--trailer' options until the next occurrence of
	'--if-missing' or '--no-if-missing'. 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 following configured `trailer.*`
	rules.

	--unfold::
	Remove any whitespace-continuation in trailers, so that each
	trailer appears on a line by itself with its full content.

	--parse::
	A convenience alias for `--only-trailers --only-input
	--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 "%=$", then only lines
	using the format '<token><sep><value>' with <sep> containing '%', '='
	or '$' and then spaces will be considered trailers. And '%' will be
	the default separator used, so by default trailers will appear like:
	'<token>% <value>' (one percent sign and one space will appear between
	the token 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 <token>.
	+
	If it is `before`, then each new trailer will appear just before the
	first trailer with the same <token>.

	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 <token> in the message.
	+
	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 (<token>, <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 (<token>, <value>) pair is already in the message.
	+
	With `add`, a new trailer will be added, even if some trailers with
	the same (<token>, <value>) pair are already in the message.
	+
	With `replace`, an existing trailer with the same <token> will be
	deleted and the new trailer will be added. The deleted trailer will be
	the closest one (with the same <token>) 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 <token> in the message.

	trailer.ifmissing::
	This option makes it possible to choose what action will be
	performed when there is not yet any trailer with the same
	<token> in the message.
	+
	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.<token>.key::
	This `key` will be used instead of <token> in the trailer. At
	the end of this 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, then the key will be used instead of both the
	<token> and the default separator when adding the trailer.

	trailer.<token>.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 <token>.

	trailer.<token>.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 <token>.

	trailer.<token>.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 <token>.

	trailer.<token>.command::
	This option can be used to specify a shell command that will
	be called to automatically add or modify a trailer with the
	specified <token>.
	+
	When this option is specified, the behavior is as if a special
	'<token>=<value>' argument were added at the beginning of the command
	line, where <value> is taken to be the standard output of the
	specified command with any leading and trailing whitespace trimmed
	off.
	+
	If the command contains the `$ARG` string, this string will be
	replaced with the <value> part of an existing trailer with the same
	<token>, if any, before the command is launched.
	+
	If some '<token>=<value>' arguments are also passed on the command
	line, when a 'trailer.<token>.command' is configured, the command will
	also be executed for each of these arguments. And the <value> part of
	these arguments, if any, will be used to replace the `$ARG` string in
	the command.

	EXAMPLES
	--------

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

	message
	$ cat msg.txt \| git interpret-trailers --trailer 'sign: Alice <alice@example.com>' --trailer 'sign: Bob <bob@example.com>'
	subject

	message

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

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

	message

	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

	message

	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:
	+
	------------
	$ git config trailer.sign.key "Signed-off-by: "
	$ git config trailer.sign.ifmissing add
	$ git config trailer.sign.ifexists doNothing
	$ git config trailer.sign.command 'echo "$(git config user.name) <$(git config user.email)>"'
	$ git interpret-trailers <<EOF
	> EOF

	Signed-off-by: Bob <bob@example.com>
	$ git interpret-trailers <<EOF
	> Signed-off-by: Alice <alice@example.com>
	> EOF

	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 'see' trailer with a command to show the subject of a
	commit that is related, and show how it works:
	+
	------------
	$ git config trailer.see.key "See-also: "
	$ git config trailer.see.ifExists "replace"
	$ git config trailer.see.ifMissing "doNothing"
	$ git config trailer.see.command "git log -1 --oneline --format=\"%h (%s)\" --abbrev-commit --abbrev=14 \$ARG"
	$ git interpret-trailers <<EOF
	> subject
	>
	> message
	>
	> see: HEAD~2
	> EOF
	subject

	message

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