display user's login name
logname utility writes the user's
login name to standard output followed by a newline
logname utility explicitly ignores the
variables because the environment cannot be trusted.
logname utility exits 0 on
success, and >0 if an error occurs.
who(1), whoami(1), getlogin(2)
logname utility is compliant with the
IEEE Std 1003.1-2008 (“POSIX.1”)
logname command first appeared in
PWB/UNIX 1.0 and was reimplemented for