In Unix and Unix-like operating systems, write is a utility used to send messages to another user by writing a message directly to another user's TTY.
The write command was included in the First Edition of the Research Unix operating system.
The syntax for the write command is:
$ write user [tty]
The write session is terminated by sending EOF, which can be done by pressing Ctrl+D. The tty argument is only necessary when a user is logged into more than one terminal.
A conversation initiated between two users on the same machine:
$ write root pts/7
Will show up to the user on that console as:
Message from root@wiki on pts/8 at 11:19 ...