NAME

write — write to another user

SYNOPSIS

write user_name [terminal]

DESCRIPTION

The write utility shall read lines from the standard input and write them to the terminal of the specified user. When first invoked, it shall write the message:

Message from sender-login-id (sending-terminal) [date]...

to user_name. When it has successfully completed the connection, the sender's terminal shall 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 an NL, EOF, or EOL special character (see XBD 11. General Terminal Interface) is accumulated while in canonical input mode, the accumulated data shall be written on the other user's terminal. Characters shall be processed as follows:

• Typing <alert> shall write the <alert> character to the recipient's terminal.

• Typing the erase and kill characters shall affect the sender's terminal in the manner described by the termios interface in XBD 11. General Terminal Interface.

• Typing the interrupt or end-of-file characters shall cause write to write an appropriate message ("EOT\n" in the POSIX locale) to the recipient's terminal and exit.

• Typing characters from LC_CTYPE classifications print or space shall cause those characters to be sent to the recipient's terminal.

• When and only when the stty iexten local mode is enabled, the existence and processing of additional special control characters and multi-byte or single-byte functions is implementation-defined.

• Typing other non-printable characters shall cause implementation-defined sequences of printable characters to be written to the recipient's terminal.

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 selected in an implementation-defined manner and an informational message is written to the sender's standard output, indicating which terminal was chosen.

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 shall fail when the user lacks appropriate privileges to perform the requested action.

OPTIONS

None.

OPERANDS

The following operands shall be supported:

user_name

Login name of the person to whom the message shall be written. The application shall ensure that this operand is of the form returned by the who utility.

terminal

Terminal identification in the same format provided by the who utility.

STDIN

Lines to be copied to the recipient's terminal are read from standard input.

INPUT FILES

None.

ENVIRONMENT VARIABLES

The following environment variables shall affect the execution of write:

LANG

Provide a default value for the internationalization variables that are unset or null. (See XBD 8.2 Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)

LC_ALL

If set to a non-empty string value, override the values of all the other internationalization variables.

LC_CTYPE

Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments and input files). If the recipient's locale does not use an LC_CTYPE equivalent to the sender's, the results are undefined.

LC_MESSAGES

Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error and informative messages written to standard output.

NLSPATH

^[XSI] Determine the location of messages objects and message catalogs.

ASYNCHRONOUS EVENTS

If an interrupt signal is received, write shall write an appropriate message on the recipient's terminal and exit with a status of zero. It shall take the standard action for all other signals.

STDOUT

An informational message shall be written to standard output if a recipient is logged in more than once.

STDERR

The standard error shall be used only for diagnostic messages.

OUTPUT FILES

The recipient's terminal is used for output.

EXTENDED DESCRIPTION

None.

EXIT STATUS

The following exit values shall be returned:

 0

Successful completion.

>0

The addressed user is not logged on or the addressed user denies permission.

CONSEQUENCES OF ERRORS

Default.

APPLICATION USAGE

The talk utility is considered by some users to be a more usable utility on full-screen terminals.

EXAMPLES

None.

RATIONALE

The write utility was included in this volume of POSIX.1-2024 since it can be implemented on all terminal types. The standard developers considered the talk utility, which cannot be implemented on certain terminals, to be a "better" communications interface. Both of these programs are in widespread use on historical implementations. Therefore, the standard developers decided that both utilities should be specified.

The format of the terminal name is unspecified, but the descriptions of ps, talk, who, and write require that they all use or accept the same format.

FUTURE DIRECTIONS

None.

SEE ALSO

mesg, talk, who

XBD 8. Environment Variables, 11. General Terminal Interface

CHANGE HISTORY

First released in Issue 2.

Issue 5

The FUTURE DIRECTIONS section is added.

Issue 6

This utility is marked as part of the User Portability Utilities option.

The normative text is reworded to avoid use of the term "must" for application requirements.

Issue 7

The write utility is moved from the User Portability Utilities option to the Base. User Portability Utilities is now an option for interactive utilities.

Issue 8

Austin Group Defect 1122 is applied, changing the description of NLSPATH .