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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.1‐2017,
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.1‐2017,  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.

       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.1‐2017 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.1‐2017.

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.1‐2017 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.1‐2017 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
       1003.1-2017,  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 .