print names of those who have sent mail
from [-c] [-f file] [-s sender] [user]
The from utility prints out the mail header lines from the invoker's mailbox. The following options are available: -c Just print a count of messages and exit. -f file The supplied file is examined instead of the invoker's mailbox. If the -f option is used, the user argument should not be used. Read from standard input if file name “-” is given. -s sender Only mail from addresses containing the supplied string are printed. If user is given, the user's mailbox is examined instead of the invoker's own mailbox. (Privileges are required.)
MAIL If set, the location of the invoker's mailbox. Otherwise, the default in /var/mail is used.
The from command appeared in 3.0BSD.