TALK(1P) POSIX Programmer's Manual TALK(1P)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.
NAMEtalk — talk to another user
SYNOPSIStalk address [terminal]
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:
Once communication is established, the two parties can type simultane‐
ously, 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
* Typing the erase and kill characters shall affect the sender's ter‐
minal in the manner described by the termios interface in the Base
Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal
* 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 noth‐
ing except exit.
* Typing characters from LC_CTYPE classifications print or space
shall cause those characters to be sent to the recipient's termi‐
* When and only when the stty iexten local mode is enabled, the exis‐
tence and processing of additional special control characters and
multi-byte or single-byte functions shall be implementation-
* Typing other non-printable characters shall cause implementation-
defined sequences of printable characters to be sent to the recipi‐
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 simulta‐
neous interaction or it may report an error describing the terminal-
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.
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.
The following environment variables shall affect the execution of talk:
LANG Provide a default value for the internationalization vari‐
ables that are unset or null. (See the Base Definitions vol‐
ume of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
ables 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.
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
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.
When the talk utility receives a SIGINT signal, the utility shall ter‐
minate and exit with a zero status. It shall take the standard action
for all other signals.
If standard output is a terminal, characters copied from the recipi‐
ent'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.
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred or talk was invoked on a terminal incapable of
CONSEQUENCES OF ERRORS
The following sections are informative.
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
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 can‐
not be implemented on certain terminals, was considered to be a ``bet‐
ter'' communications interface. Both of these programs are in wide‐
spread 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
Historical BSD and System V versions of talk terminate both of the con‐
versations 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 interna‐
tionalized 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 irrele‐
* Subsequent communication between the two parties cannot be interna‐
tionalized 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
The text in the STDOUT section reflects the usage of the verb ``dis‐
play'' 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
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 rea‐
sons, disallow the transmission of non-printable characters that may
send commands to the other terminal.
mesg, stty, who, write
The Base Definitions volume of POSIX.1‐2008, 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, 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 Electri‐
cal 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
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IEEE/The Open Group 2013 TALK(1P)