git-interpret-trailers(1) Git Manual git-interpret-trailers(1)
NAME
git-interpret-trailers - Add or parse metadata in commit messages
SYNOPSIS
git interpret-trailers [--in-place] [--trim-empty]
[(--trailer (<key>|<key-alias>)[(=|:)<value>])...]
[--parse] [<file>...]
DESCRIPTION
Add or parse trailer metadata at the end of the otherwise free-form part
of a commit message, or any other kind of text.
A trailer in its simplest form is a key-value pair with a colon as a
separator. The key consists of ASCII alphanumeric characters and hyphens
(-). A trailer block consists of one or more trailers. The trailer block
needs to be preceded by a blank line, where a blank line is either an
empty or a whitespace-only line. 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.<key-alias> 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.
Let's consider new trailers added with --trailer. By default, the new
trailer will appear at the end of the trailer block. Also by default,
this new trailer will only be added if the last trailer is different to
it. A trailer block will be created with only that trailer if a trailer
block does not already exist. Recall that a trailer block needs to be
preceded by a blank line, so a blank line will be inserted before the new
trailer block in that case.
This is how the new trailer is added: a <key>=<value> or <key>:<value>
argument given using --trailer will be appended after the existing
trailers. 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).
Existing trailers are extracted from the input by looking for the trailer
block. A trailer block is 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 trailer block is by
definition at the end of the commit message. The message in turn is
either (i) at the end of the input, or (ii) the last non-whitespace lines
before a line that starts with --- (followed by a space or the end of the
line).
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 <key-alias> 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".
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.
OTHER RULES
What was covered in the previous section are the rules that are relevant
for regular use. The following points are included for completeness.
o This command ignores comment lines (see core.commentString in git-
config(1)). This is for use with the prepare-commit-msg and
commit-msg hooks.
o Candidate trailer lines that have : as the separator, that have no
whitespace before the value part, and that start with // are not
recognized as trailers. This is to avoid accidentally interpreting
URLs as trailers (e.g. lines that start with https://).
OPTIONS
--in-place, --no-in-place
Edit the files in place. The default is --no-in-place.
--trim-empty, --no-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.
The default is --no-trim-empty.
--trailer=<key>[(=|:)<value>], --no-trailer
Specify a (<key>, <value>) pair that should be applied as a trailer
to the inputs. See the description of this command. Can be given
multiple times.
Use --no-trailer to reset the list.
--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.<key-alias>.where configuration variables and applies to all
--trailer options until the next occurrence of --where or --no-where.
Possible placements are after, before, end or start.
Use --no-where to clear the effect of any previous use of --where,
such that the relevant configuration variables are no longer
overridden.
--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.<key-alias>.ifExists 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.
Use --no-if-exists to clear the effect of any previous use of
--if-exists, such that the relevant configuration variables are no
longer overridden.
--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.<key-alias>.ifMissing 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.
Use --no-if-missing to clear the effect of any previous use of
--if-missing, such that the relevant configuration variables are no
longer overridden.
--only-trailers, --no-only-trailers
Output only the trailers, not any other parts of the input. The
default is --no-only-trailers.
--only-input, --no-only-input
Output only trailers that exist in the input; do not add any from the
command-line or by applying trailer.<key-alias> configuration
variables. The default is --no-only-input.
--unfold, --no-unfold
If a trailer has a value that runs over multiple lines (aka
"folded"), reformat the value into a single line. The default is
--no-unfold.
--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.
There is no convenience alias to negate this alias.
--divider, --no-divider
Treat --- as the end of the commit message. This is the default. Use
--no-divider when you know your input contains just the commit
message itself (and not an email or the output of git-format-
patch(1)).
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.<key-alias>.key
Defines a <key-alias> for the <key>. The <key-alias> 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 <key-alias>. This configuration allows the shorter --trailer
"ack:..." invocation on the command line using the "ack" <key-alias>
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.<key-alias>.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 <key-alias>.
trailer.<key-alias>.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 <key-alias>.
trailer.<key-alias>.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 <key-alias>.
trailer.<key-alias>.command
Deprecated in favor of trailer.<key-alias>.cmd. This option behaves
in the same way as trailer.<key-alias>.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.<key-alias>.cmd and trailer.<key-alias>.command are
given for the same <key-alias>, trailer.<key-alias>.cmd is used and
trailer.<key-alias>.command is ignored.
trailer.<key-alias>.cmd
This option can be used to specify a shell command that will be
called once to automatically add a trailer with the specified
<key-alias>, and then called each time a --trailer
<key-alias>=<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 <key-alias>, the behavior is as if a special --trailer
<key-alias>=<value> argument was added at the beginning of git-
interpret-trailers(1), where <value> is taken to be the standard
output of the command with any leading and trailing whitespace
trimmed off.
If some --trailer <key-alias>=<value> arguments are also passed on
the command line, the command is called again once for each of these
arguments with the same <key-alias>. 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 <key-alias>=<value> argument.
EXAMPLES
o 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>
o 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>
o 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
o 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>
o 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
o 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>
o 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)
o 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)
o 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(1) 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
o Here we try to use three different trailer keys. But it fails because
two of them are not recognized as trailer keys.
$ cat msg.txt
subject
Skapad-pa: some-branch
Hash-in-v6.11: 45c12d3269fe48f22834320c782ffe86c3560f2c
Reviewed-by: Alice <alice@example.com>
$ git interpret-trailers --only-trailers <msg.txt
$
Recall that a trailer key has to consist of only ASCII alphanumeric
characters and hyphens, and this does not hold for the two first
supposed trailer keys. And now none are recognized as trailers
because the candidate trailer block has at least one non-trailer
line, even though Reviewed-by is a valid trailer key. Recall that a
trailer block has to either (i) be all trailers, or (ii) consist of
at least one Git-generated or user-configured trailer (and some other
conditions). And (ii) is not satisfied since we have not configured
any trailer keys.
SEE ALSO
git-commit(1), git-format-patch(1), git-config(1)
GIT
Part of the git(1) suite
Git 2.56.0 2026-09-27 git-interpret-trailers(1)
git 2.56.0 - Generated Thu Oct 1 16:25:20 CDT 2026