Logname

logname shows the current login name.

Provided by
Most (all?) Linux distributions incorporate this from the GNU Coreutils: and use its man page

Related Commands
All of these relate to user information.
 * id - dump UID and GID information.
 * whoami - show effective user ID.
 * groups - show groups of the current user.
 * users - show who is logged in.
 * who - show who is logged in from where.