TALK(P) POSIX Programmer's Manual TALK(P)
talk - talk to another user
talk 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_addresstalk: 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 simultaneously, with their
output displayed in separate regions of the screen. Characters shall be processed as fol-
* 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
IEEE Std 1003.1-2001, 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 ses-
sion 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 char-
acters 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
* 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 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 lev-
els of simultaneous interaction or it may report an error describing the terminal-related
The following operands shall be supported:
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
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 mes-
sage shall be displayed on one or more accessible terminals in use by the recipi-
ent. 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 variables that are unset or
null. (See the Base Definitions volume of IEEE Std 1003.1-2001, Section 8.2, Inter-
nationalization 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 interna-
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 argu-
ments and input files). If the recipient's locale does not use an LC_CTYPE equiva-
lent to the sender's, the results are undefined.
Determine the locale that should be used to affect the format and contents of diag-
nostic messages written to standard error and informative messages written to stan-
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.
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.
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 mes-
sages. 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 supporting it.
CONSEQUENCES OF ERRORS
The following sections are informative.
Because the handling of non-printable, non- <space>s 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 IEEE Std 1003.1-2001 since it can be
implemented on all terminal types. The talk utility, which cannot be implemented on cer-
tain 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 IEEE Std 1003.1-2001.
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 termi-
nates 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 internationalized in any
* 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
* 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 exam-
ple, 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 reasons, disallow the transmission of non-printable charac-
ters that may send commands to the other terminal.
mesg , stty , who , write , the Base Definitions volume of IEEE Std 1003.1-2001, Chapter
11, General Terminal Interface
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 TALK(P)