| BIFF(1) | General Commands Manual | BIFF(1) | 
biff —
| biff | [ n|y] | 
biff informs the system whether you want to be notified
  when mail arrives during the current terminal session.
Options supported by biff:
When mail notification is enabled, the header and first few lines
    of the message will be printed on your screen whenever mail arrives. A
    “biff y” command is often included in
    the file .login or .profile
    to be executed at each login.
When no arguments are present, biff
    displays the current notification status to the standard output.
biff operates asynchronously. For
    synchronous notification use the MAIL variable of
    sh(1) or the
    mail variable of
    csh(1).
biff utility exits with one of the following values:
biff command appeared in
  4.0BSD.
| December 20, 2016 | NetBSD 10.1 |