While playing around with Git hooks I found one not very popular, but useful, command - interpret-trailers.
Turns out keywords and metadata added (usually) at the end of the commit message are called trailers.
For example in
Commit title
Commit body
JIRA: PRJ-1234
Signed-off-by: Alice <alice@example.com>
and
Commit title
Commit body
Fixes #2
JIRA: PRJ-1234, Signed-off-by: Alice <alice@example.com> and Fixes #2 are all trailers.
Key-value pairs separated with empty line from the free-form commit message.
interpret-trailers can read, add or replace the trailers from given commit message.
It is quite useful for Git hooks or in automation such as GitHub Actions.
I've used it to create simple commit hook that adds JIRA: NA to commit message if no JIRA is referenced.
The official documentation gives more details and several nice examples that show different usages of the command.