PROLOG

       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.

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 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.

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  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.)

       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   Determine the location of message catalogs for the processing of LC_MESSAGES.

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.

       The following sections are informative.

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.1‐2017 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.

FUTURE DIRECTIONS

       None.

SEE ALSO

       mesg, talk, who

       The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment Variables, Chapter 11,
       General Terminal Interface

COPYRIGHT

       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 .