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

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

+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 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 2.48.1 2025-01-13 GIT-INTERPRET-TRAILERS(1)