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Message from sender-login-id (sending-terminal) [date]...
to user. When it has successfully completed the connection, the sender’s terminal will be alerted twice to indicate that what the sender is typing is being written to the recipient’s terminal.
If the recipient wants to reply, this can be accomplished by typing
write sender-login-id [sending-terminal]
upon receipt of the initial message. Whenever a line of input as delimited by a NL , EOF , or EOL special character is accumulated while in canonical input mode, the accumulated data will be written on the other user’s terminal. Characters are processed as follows:
- Typing the alert character will write the alert character to the recipient’s terminal.
- Typing the erase and kill characters will affect the sender’s terminal in the manner described by the termios(3) interface.
- Typing the interrupt or end-of-file characters will cause write to write an appropriate message (EOT \n in the "C" locale) to the recipient’s terminal and exit.
- Typing characters from LC_CTYPE classifications print or space will cause those characters to be sent to the recipient’s terminal.
- When and only when the stty iexten local mode is enabled, additional special control characters and multi-byte or single-byte characters are processed as printable characters if their wide character equivalents are printable.
- Typing other non-printable characters will cause them to be written to the recipient’s terminal as follows: control characters will appear as a ‘^’ followed by the appropriate ASCII character, and characters with the high-order bit set will appear in ‘meta’ notation. For example, ‘\003’ is displayed as ‘^C’ and ‘\372’ as ‘M-z’.
To write to a user who is logged in more than once, the terminal argument can be used to indicate which terminal to write to; otherwise, the recipient’s terminal is the first writable instance of the user found in /usr/adm/utmp, and the following informational message will be written to the sender’s standard output, indicating which terminal was chosen:
user is logged on more than one place. You are connected to terminal. Other locations are: terminal
Permission to be a recipient of a write message can be denied or granted by use of the mesg utility. However, a user’s privilege may further constrain the domain of accessibility of other users’ terminals. The write utility will fail when the user lacks the appropriate privileges to perform the requested action.
If the character ! is found at the beginning of a line, write calls the shell to execute the rest of the line as a command.
write runs setgid() (see setuid(2) ) to the group ID tty, in order to have write permissions on other user’s terminals.
The following protocol is suggested for using write: when you first write to another user, wait for them to write back before starting to send. Each person should end a message with a distinctive signal (that is, (o) for ‘‘over’’) so that the other person knows when to reply. The signal (oo) (for ‘‘over and out’’) is suggested when conversation is to be terminated.