Documentation/git-interpret-trailers.adoc - 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

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


            include::includes/cmd-config-section-all.adoc[]


            include::config/trailer.adoc[]


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

	include::includes/cmd-config-section-all.adoc[]

	include::config/trailer.adoc[]

	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