This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
write user_name [terminal]
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 the Base Definitions volume of POSIX.1-2017, Chapter 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 the Base Definitions volume of POSIX.1-2017, Chapter 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.
The following operands shall be supported:
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 identification in the same format provided by the who utility.
Lines to be copied to the recipient's terminal are read from standard input.
The following environment variables shall affect the execution of write:
Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1-2017, Section 8.2, Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
If set to a non-empty string value, override the values of all the other internationalization variables.
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.
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.
Determine the location of message catalogs for the processing of LC_MESSAGES.
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.
An informational message shall be written to standard output if a recipient is logged in more than once.
The standard error shall be used only for diagnostic messages.
The recipient's terminal is used for output.
The following exit values shall be returned:
The addressed user is not logged on or the addressed user denies permission.
Consequences of Errors
The following sections are informative.
The talk utility is considered by some users to be a more usable utility on full-screen terminals.
The write utility was included in this volume of POSIX.1-2017 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.
mesg, talk, who
The Base Definitions volume of POSIX.1-2017, Chapter 8, Environment Variables, Chapter 11, General Terminal Interface
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .
logger(1p), mesg(1p), talk(1p).