GIT-INTERPRET-TRAILERS(1)	  Git Manual	     GIT-INTERPRET-TRAILERS(1)

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

SYNOPSIS
       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 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
       Everything below this line in this section is selectively included from
       the git-config(1) documentation. The content is the same as what’s
       found there:

       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
       git-commit(1), git-format-patch(1), git-config(1)

GIT
       Part of the git(1) suite

Git 2.51.0			  2025-08-17	     GIT-INTERPRET-TRAILERS(1)