How to specify commit author on the fly?

I want to do a commit in a repo. I don't want to set me as the default person signing, i.e. want to avoid git config --global user.email "you@example.com" and git config --global user.name "Your Name". So I am doing git commit -m "Message" --author="My Name <my_email@email.com>", but Git says

Committer identity unknown

*** Please tell me who you are.

Run

  git config --global user.email "you@example.com"
  git config --global user.name "Your Name"

to set your account's default identity.
Omit --global to set the identity only in this repository.

How can I sign only this commit?

Try to set GIT_AUTHOR_NAME and GIT_AUTHOR_EMAIL environment variables before your commit. See the explanation about this.

#!/bin/bash
GIT_AUTHOR_NAME="Your Name" GIT_AUTHOR_EMAIL=you@example.com git commit -m "Message"

As far as I know, I don't think you can avoid editing your configuration. However, you can remove the --global flag and it will save the name/email for the local repository instead of overwriting your global settings.

So you could set the local configuration, sign the commit, then unset the configuration:

git config --global user.email "you@example.com"
git config --global user.name "Your Name"
git commit -m "Message"
git config --unset user.email
git config --unset user.name

Which I admit is a bit tedious, especially if you are committing this way frequently.

You can also edit this local configuration file with git config --edit, where you can comment out your name/email whenever you want to "sign out".