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 byyour_addresstalk: respond with: talkyour_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 follows:
Typing the alert character shall alert the recipient's
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 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 sttyiexten local mode
is enabled, the existence and processing of additional special control
characters and multi-byte or single-byte functions shall be
Typing other non-printable characters shall cause
implementation-defined sequences of printable characters to be sent to the
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 simultaneous
interaction or it may report an error describing the terminal-related
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 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
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:
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
Variables for the precedence of internationalization variables used to
determine the values of locale categories.)
If set to a non-empty string value, override the values of
all the other internationalization variables.
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.
Determine the location of message catalogs for the
processing of LC_MESSAGES.
Determine the name of the invoker's terminal type. If this
variable is unset or null, an unspecified default terminal type shall be
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.
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 sequences.
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 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 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 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
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 characters that may send commands to the other
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