man > GIT-INTERPRET-TRAILERS(1)

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>|<keyAlias>)[(=|:)<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 AT example.com>
           Signed-off-by: Bob <bob AT 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 <keyAlias> can be configured to make using --trailer shorter to type on
       the command line. This can be configured using the trailer.<keyAlias>.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 AT example.com>' --trailer 'sign: Bob <bob AT example.com>' <msg.txt
               subject

               body text

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

               body text

               Signed-off-by: Bob <bob AT example.com>
               Acked-by: Alice <alice AT 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 AT example.com>' --trailer 'Reviewed-by: Bob <bob AT 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 AT example.com>
               $ cat msg2.txt
               subject

               body text

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

               body text

               Signed-off-by: Alice <alice AT 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 AT pobox.com>
               Helped-by: Christian Couder <christian.couder AT 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 2.43.0                                   07/02/2025                    GIT-INTERPRET-TRAILERS(1)