GIT-INTERPRET-TRAILERS(1)

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

okay so bestie, this is GIT-INTERPRET-TRAILERS(1) from the Git Manual, and it’s lowkey iconic for commit-message metadata. let’s get into it 💅

🌸 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. literally any text, bestie.

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. yes bestie, those are the 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. so it’s just the raw trailer tea ✨

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. so yes, the patch part stays untouched unless you say otherwise 🫶

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. automatic trailer behavior, we love to see it 😭

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. okay so it’s giving “respect the blank line” energy 💀

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). one colon, one space, no chaos 💅

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). bestie, that’s the whole trailer-block vibe check ✨

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". short and slay, no cap 🎀

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. so these are the extra-lore rules, iykyk 🦋

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.
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://). protecting us from accidental URL trailer nonsense, iconic behavior 💅

🎀 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 💖

okay so everything under this line is selectively pulled from the git-config(1) docs — bestie, the content is literally the exact same as what's over there, we're just serving it with better vibes 🫶

🎀 `trailer.separators`

this one tells you which characters get recognized as trailer separators. by default only : counts as a trailer separator — EXCEPT that = is always accepted on the command line for compatibility with other git commands (she's grandfathered in, iconic 💅).

the first character you give this option becomes the default character used when another separator isn't specified in the config for that trailer.

so like, 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> — that's one percent sign and one space sitting between the key and the value ✨

🦋 `trailer.where`

this option tells you where a new trailer will be added. the values can be end, which is the default, start, after, or before 👑

if it's end, then each new trailer will appear at the end of the existing trailers
if it's start, then each new trailer will appear at the start, instead of the end, of the existing trailers
if it's after, then each new trailer will appear just after the last trailer with the same <key>
if it's before, then each new trailer will appear just before the first trailer with the same <key>

🌸 `trailer.ifexists`

this one lets you pick what action gets performed when there's already at least one trailer with the same <key> in the input. the valid values are: addIfDifferentNeighbor (the default, bestie 🎀), 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's already one with the same <key> in the input

💜 `trailer.ifmissing`

this one's the mirror of the last one — it lets you choose what action gets performed when there is not yet any trailer with the same <key> in the input. the valid values are add (the default ✨) and doNothing.

with add, a new trailer will be added
with doNothing, nothing will be done

🧚 `trailer.<key-alias>.key`

this defines a <key-alias> for the <key>. the <key-alias> must be a prefix (case does not matter) of the <key> 👀

so for example, in git config trailer.ack.key "Acked-by" the Acked-by is the <key> and the ack is the <key-alias>. this config is what allows you to use the shorter --trailer "ack:..." invocation on the command line with the "ack" <key-alias> instead of the longer --trailer "Acked-by:...". so much typing saved, we love efficiency 🫶

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.

and 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 that option specifies for trailers with the specified <key-alias>. so it's like, local rule beats global rule, periodt ✨

💀 `trailer.<key-alias>.ifexists`

same deal — this option takes the same values as the trailer.ifexists configuration variable, and it overrides what's specified by that option for trailers with the specified <key-alias>.

🍓 `trailer.<key-alias>.ifmissing`

yup, this one too: it takes the same values as the trailer.ifmissing configuration variable and overrides what that option specifies for trailers with the specified <key-alias>.

🙈 `trailer.<key-alias>.command`

⚠️ deprecated in favor of trailer.<key-alias>.cmd, bestie — she's old news 😭

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 the 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 💀 (like, genuinely not safe, don't @ me)

and 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. cmd wins, no debate 👑

🔥 `trailer.<key-alias>.cmd`

this option lets you 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. she's got main character energy fr fr 👑

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 ✂️

and 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>. 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. cute little feedback loop, honestly obsessed 💖

✨ EXAMPLES ✨

Okay bestie, this is the part where it all clicks. Real commands, real output, no cap. Every single one is here exactly as it goes down. 🫶

Configure a sign trailer with a Signed-off-by key, 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 using a script glog-find-author which searches for a specified author identity from git log in the 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 using a script glog-grep to grep the 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(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

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-på: some-branch
Hash-in-v6.11: 45c12d3269fe48f22834320c782ffe86c3560f2c
Reviewed-by: Alice <alice@example.com>
$ git interpret-trailers --only-trailers <msg.txt
$

Okay so real talk: a trailer key has to consist of only ASCII alphanumeric characters and hyphens, and that does not hold for the first two 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. Remember: 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 here since we haven't configured any trailer keys. 💀

🌈 SEE ALSO 🌈

👑 GIT 👑

Part of the git(1) suite. Iconic behavior, honestly.

That's the whole page, bestie — you made it to the end! 🎀 This was Git 2.56.0, dated 2026-09-27, and the page is GIT-INTERPRET-TRAILERS(1). Go forth and trailer responsibly. 💅✨

📦 where this page comes from

arch rolling: git 2.56.0-1 · GPL-2.0-only
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash-1017 on 2026-11-06: a language model's rewrite of the original, under its terms

GIT-INTERPRET-TRAILERS(1)