Is there a way to get the name of the user, given only their username?
Something like this output
git show <username>
name: First Last
There are no "usernames" in Git.
When creating a commit with Git it uses the configuration values of
user.name (the real name) and
user.email (email address). Those config values can be overridden on the console by setting and exporting the environment variables
Git doesn't know anything about github's users, because github is not part of Git. (It always makes me sad when I get the impression that a lot of people think that).
So you're only left with an API call to github (I guess you could do that from the commandline with a little scripting)