git interpret-trailers: Usage, Options & Common CI Errors
git interpret-trailers reads and writes the key/value footers at the end of commit messages.
Trailers like Signed-off-by, Reviewed-by, or Co-authored-by power DCO checks and changelog tooling. This command adds or extracts them deterministically, which makes it ideal for commit hooks and CI.
What it does
git interpret-trailers parses the trailer block at the end of a commit message and can add, replace, or normalize trailers according to configured rules, reading the message from a file or standard input.
Common usage
git interpret-trailers --trailer "Signed-off-by: A <a@x.io>" msg.txt
git interpret-trailers --parse < commit-msg.txt
git log -1 --format=%B | git interpret-trailers --parse
echo "msg" | git interpret-trailers --trailer "Reviewed-by: B <b@x.io>"Options
| Flag | What it does |
|---|---|
| --trailer <token>=<value> | Add a trailer |
| --parse | Output only the parsed trailers |
| --if-exists <action> | addIfDifferent / replace / doNothing |
| --if-missing <action> | add / doNothing when absent |
| --in-place | Edit the file in place |
Common errors in CI
A common DCO failure is a missing Signed-off-by trailer; pipe the message through --parse and assert the token exists. Note that lines must form a valid trailer block (no blank lines inside it) or --parse returns nothing, which scripts can misread as "no sign-off".