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.TH TALK "1P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"

.SH 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.

.SH NAME

talk

\(em talk to another user

.SH SYNOPSIS

.LP

.nf

talk \fIaddress \fB[\fIterminal\fB]\fR

.fi

.SH DESCRIPTION

The

.IR talk

utility is a two-way, screen-oriented communication program.

.P

When first invoked,

.IR talk

shall send a message similar to:

.sp

.RS 4

.nf

\fB

Message from <\fIunspecified string\fP>

talk: connection requested by \fIyour_address\fP

talk: respond with: talk \fIyour_address\fP

.fi \fR

.P

.RE

.P

to the specified

.IR address .

At this point, the recipient of the message can reply by typing:

.sp

.RS 4

.nf

\fB

talk \fIyour_address\fR

.fi \fR

.P

.RE

.P

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:

.IP " *" 4

Typing the

<alert>

character shall alert the recipient's terminal.

.IP " *" 4

Typing <control>\(hyL shall cause the sender's screen regions to be

refreshed.

.IP " *" 4

Typing the erase and kill characters shall affect the sender's terminal

in the manner described by the

.BR termios

interface in the Base Definitions volume of POSIX.1\(hy2008,

.IR "Chapter 11" ", " "General Terminal Interface".

.IP " *" 4

Typing the interrupt or end-of-file characters shall terminate the

local

.IR talk

utility. Once the

.IR talk

session has been terminated on one side, the other side of the

.IR talk

session shall be notified that the

.IR talk

session has been terminated and shall be able to do nothing except

exit.

.IP " *" 4

Typing characters from

.IR LC_CTYPE

classifications

.BR print

or

.BR space

shall cause those characters to be sent to the recipient's terminal.

.IP " *" 4

When and only when the

.IR stty

.BR 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.

.IP " *" 4

Typing other non-printable characters shall cause

implementation-defined sequences of printable characters to be sent

to the recipient's terminal.

.P

Permission to be a recipient of a

.IR talk

message can be denied or granted by use of the

.IR mesg

utility. However, a user's privilege may further constrain the domain

of accessibility of other users' terminals. The

.IR talk

utility shall fail when the user lacks appropriate privileges to

perform the requested action.

.P

Certain block-mode terminals do not have all the capabilities necessary

to support the simultaneous exchange of messages required for

.IR 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.

.SH OPTIONS

None.

.SH OPERANDS

The following operands shall be supported:

.IP "\fIaddress\fR" 10

The recipient of the

.IR talk

session. One form of

.IR address

is the <\fIuser\ name\fP>, as returned by the

.IR who

utility. Other address formats and how they are handled are

unspecified.

.IP "\fIterminal\fR" 10

If the recipient is logged in more than once, the

.IR terminal

argument can be used to indicate the appropriate terminal name. If

.IR terminal

is not specified, the

.IR talk

message shall be displayed on one or more accessible terminals in use

by the recipient. The format of

.IR terminal

shall be the same as that returned by the

.IR who

utility.

.SH 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.

.SH "INPUT FILES"

None.

.SH "ENVIRONMENT VARIABLES"

The following environment variables shall affect the execution of

.IR talk :

.IP "\fILANG\fP" 10

Provide a default value for the internationalization variables that are

unset or null. (See the Base Definitions volume of POSIX.1\(hy2008,

.IR "Section 8.2" ", " "Internationalization Variables"

for the precedence of internationalization variables used to determine

the values of locale categories.)

.IP "\fILC_ALL\fP" 10

If set to a non-empty string value, override the values of all the

other internationalization variables.

.IP "\fILC_CTYPE\fP" 10

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

.IR LC_CTYPE

equivalent to the sender's, the results are undefined.

.IP "\fILC_MESSAGES\fP" 10

.br

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.

.IP "\fINLSPATH\fP" 10

Determine the location of message catalogs for the processing of

.IR LC_MESSAGES .

.IP "\fITERM\fP" 10

Determine the name of the invoker's terminal type. If this variable is

unset or null, an unspecified default terminal type shall be used.

.SH "ASYNCHRONOUS EVENTS"

When the

.IR 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.

.SH 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,

.IR talk

shall exit with a non-zero status.

.SH STDERR

None.

.SH "OUTPUT FILES"

None.

.SH "EXTENDED DESCRIPTION"

None.

.SH "EXIT STATUS"

The following exit values shall be returned:

.IP "\00" 6

Successful completion.

.IP >0 6

An error occurred or

.IR talk

was invoked on a terminal incapable of supporting it.

.SH "CONSEQUENCES OF ERRORS"

Default.

.LP

.IR "The following sections are informative."

.SH "APPLICATION USAGE"

Because the handling of non-printable, non-\c

<space>

characters is tied to the

.IR stty

description of

.BR iexten ,

implementation extensions within the terminal driver can be accessed.

For example, some implementations provide line editing functions with

certain control character sequences.

.SH EXAMPLES

None.

.SH RATIONALE

The

.IR write

utility was included in this volume of POSIX.1\(hy2008 since it can be implemented on all

terminal types. The

.IR 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.

.P

All references to networking abilities (\fItalk\fPing to a user on

another system) were removed as being outside the scope of this volume of POSIX.1\(hy2008.

.P

Historical BSD and System V versions of

.IR 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

.IR talk

specified by this volume of POSIX.1\(hy2008 requires both users to terminate their end of the

session explicitly.

.P

Only messages sent to the terminal of the invoking user can be

internationalized in any way:

.IP " *" 4

The original ``Message from <\fIunspecified string\fP> .\|.\|.''

message sent to the terminal of the recipient cannot be

internationalized because the environment of the recipient is as yet

inaccessible to the

.IR talk

utility. The environment of the invoking party is irrelevant.

.IP " *" 4

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).

.IP " *" 4

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.

.P

The text in the STDOUT section reflects the usage of the verb

``display'' in this section; some

.IR talk

implementations actually use standard output to write to the terminal,

but this volume of POSIX.1\(hy2008 does not require that to be the case.

.P

The format of the terminal name is unspecified, but the descriptions of

.IR ps ,

.IR talk ,

.IR who ,

and

.IR write

require that they all use or accept the same format.

.P

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.

.SH "FUTURE DIRECTIONS"

None.

.SH "SEE ALSO"

.IR "\fImesg\fR\^",

.IR "\fIstty\fR\^",

.IR "\fIwho\fR\^",

.IR "\fIwrite\fR\^"

.P

The Base Definitions volume of POSIX.1\(hy2008,

.IR "Chapter 8" ", " "Environment Variables",

.IR "Chapter 11" ", " "General Terminal Interface"

.SH COPYRIGHT

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

Electrical 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 files to

man page format. To report such errors, see

https://www.kernel.org/doc/man-pages/reporting_bugs.html .