# write

## 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.
    


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