The ability of users to communicate with each other is integral to any interactive operating system. UNIX, like OpenVMS, supports communications between users on the same computer (local host) or between users on different computers (remote hosts) connected via a network. This chapter covers two commands and one utility (that is, two relatively simple programs and one relatively complex one) whereby users can communicate with each other either on a local computer or on a local and a remote computer. This chapter concentrates on communication between users on the local computer only. Chapter 13 discusses communication with remote hosts.

Note that depending on the networking protocol that is installed, OpenVMS supports either a DECnet mail address of the form NODE::USERNAME, or the Internet mail form user@host. Most OpenVMS examples in this chapter use the DECnet mail addressing form.

Communication with other users may take place in interactive or batch mode. Interactive communication requires an immediate response from the user receiving the message, who must be logged on to receive it. Batch communications do not require an immediate response from the receiver. The commands talk and write (Section 6.3) apply to interactive communication (compare with the OpenVMS commands PHONE and REPLY), whereas the mail utility (Section 6.1) applies to batch communications (compare with the OpenVMS utility MAIL). Note...