TALK(P) POSIX Programmer's Manual TALK(P)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]
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_addresstalk: 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 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
refreshed.
* 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 IEEE Std 1003.1-2001, Chapter 11, General Ter‐
minal 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 exis‐
tence 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 recipi‐
ent'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 the 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-
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 for‐
mats and how they are handled are unspecified.
terminal
If the recipient is logged in more than once, the terminal argu‐
ment 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
IEEE Std 1003.1-2001, 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.
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 vari‐
able 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 ter‐
minate 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 recipi‐
ent's standard input may be written to standard output. Standard out‐
put 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>s is tied to the
stty description of iexten, implementation extensions within the termi‐
nal 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 IEEE Std 1003.1-2001
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 utili‐
ties 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
IEEE Std 1003.1-2001.
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
IEEE Std 1003.1-2001 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 irrelevant.
* 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
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 IEEE Std 1003.1-2001 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 rea‐
sons, disallow the transmission of non-printable characters that may
send commands to the other terminal.
FUTURE DIRECTIONS
None.
SEE ALSO
mesg , stty , who , write , the Base Definitions volume of
IEEE Std 1003.1-2001, Chapter 11, General Terminal Interface
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .
IEEE/The Open Group 2003 TALK(P)
