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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

       talk — talk to another user

SYNOPSIS

       talk address [terminal]

DESCRIPTION

The talk utility is a two-way, screen-oriented communication program.

When first invoked, talk shall send a message similar to:

Message from <unspecified string>
talk: connection requested by your_address
talk: respond with: talk your_address

to the specified address. At this point, the recipient of the message can reply by typing:

talk your_address

Once communication is established, the two parties can type simultaneously, with their output displayed
in separate regions of the screen. Characters shall be processed as follows:

* Typing the <alert> character shall alert the recipient's terminal.

* Typing <control>‐L shall cause the sender's screen regions to be refreshed.

* 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.1‐2008, Chapter 11, General Terminal
Interface.

* Typing the interrupt or end-of-file characters shall terminate the local talk utility. Once the talk
session has been terminated on one side, the other side of the talk session shall be notified that
the talk session has been terminated and shall be able to do nothing except 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 shall be implementation-defined.

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

Permission to be a recipient of a talk 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 talk utility shall fail when the user lacks appropriate privileges to perform the requested action.

Certain block-mode terminals do not have all the capabilities necessary to support the simultaneous
exchange of messages required for talk. When this type of exchange cannot be supported on such
terminals, the implementation may support an exchange with reduced levels of simultaneous interaction or
it may report an error describing the terminal-related deficiency.

OPTIONS

       None.

OPERANDS

       The following operands shall be supported:

       address   The recipient of the talk session. One form of address is the <user name>, as returned  by  the
                 who utility. Other address formats and how they are handled are unspecified.

       terminal  If the recipient is logged in more than once, the terminal argument can be used to indicate the
                 appropriate terminal name. If terminal is not specified, the talk message shall be displayed on
                 one  or  more accessible terminals in use by the recipient. The format of terminal shall be the
                 same as that returned by the who utility.

STDIN

       Characters read from standard input shall be copied to the recipient's terminal in an unspecified manner.
       If  standard  input  is  not  a  terminal, talk shall write a diagnostic message and exit with a non-zero
       status.

INPUT FILES

       None.

ENVIRONMENT VARIABLES

       The following environment variables shall affect the execution of talk:

       LANG      Provide a default value for the internationalization variables that are unset or null. (See the
                 Base  Definitions  volume  of POSIX.1‐2008, 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.

       TERM      Determine the name of the invoker's terminal type. If  this  variable  is  unset  or  null,  an
                 unspecified default terminal type shall be used.

ASYNCHRONOUS EVENTS

       When  the talk utility receives a SIGINT signal, the utility shall terminate and exit with a zero status.
       It shall take the standard action for all other signals.

STDOUT

       If standard output is a terminal, characters copied from the recipient's standard input may be written to
       standard  output.  Standard  output also may be used for diagnostic messages. If standard output is not a
       terminal, talk shall exit with a non-zero status.

STDERR

       None.

OUTPUT FILES

       None.

EXTENDED DESCRIPTION

       None.

EXIT STATUS

       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred or talk was invoked on a terminal incapable of supporting it.

CONSEQUENCES OF ERRORS

       Default.

       The following sections are informative.

APPLICATION USAGE

       Because the handling of non-printable, non-<space> characters is tied to the stty description of  iexten,
       implementation  extensions within the terminal driver can be accessed.  For example, some implementations
       provide line editing functions with certain control character sequences.

EXAMPLES

       None.

RATIONALE

The write utility was included in this volume of POSIX.1‐2008 since it can be implemented on all terminal
types. The talk utility, which cannot be implemented on certain terminals, was considered to be a
``better'' communications interface. Both of these programs are in widespread use on historical
implementations. Therefore, both utilities have been specified.

All references to networking abilities (talking to a user on another system) were removed as being
outside the scope of this volume of POSIX.1‐2008.

Historical BSD and System V versions of talk terminate both of the conversations when either user breaks
out of the session. This can lead to adverse consequences if a user unwittingly continues to enter text
that is interpreted by the shell when the other terminates the session. Therefore, the version of talk
specified by this volume of POSIX.1‐2008 requires both users to terminate their end of the session
explicitly.

Only messages sent to the terminal of the invoking user can be internationalized in any way:

* The original ``Message from <unspecified string> ...'' message sent to the terminal of the recipient
cannot be internationalized because the environment of the recipient is as yet inaccessible to the
talk utility. The environment of the invoking party is irrelevant.

* Subsequent communication between the two parties cannot be internationalized because the two parties
may specify different languages in their environment (and non-portable characters cannot be mapped
from one language to another).

* Neither party can be required to communicate in a language other than C and/or the one specified by
their environment because unavailable terminal hardware support (for example, fonts) may be required.

The text in the STDOUT section reflects the usage of the verb ``display'' in this section; some talk
implementations actually use standard output to write to the terminal, but this volume of POSIX.1‐2008
does not require that to be the case.

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.

The handling of non-printable characters is partially implementation-defined because the details of
mapping them to printable sequences is not needed by the user. Historical implementations, for security
reasons, disallow the transmission of non-printable characters that may send commands to the other
terminal.

FUTURE DIRECTIONS

       None.

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers,  Inc
       and  The  Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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 .