man-pages/man1p/talk.1p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "TALK" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" talk 
.SH NAME
talk \- talk to another user
.SH SYNOPSIS
.LP
\fBtalk\fP \fIaddress\fP \fB[\fP\fIterminal\fP\fB]\fP\fB\fP
.SH DESCRIPTION
.LP
The \fItalk\fP utility is a two-way, screen-oriented communication
program.
.LP
When first invoked, \fItalk\fP shall send a message similar to:
.sp
.RS
.nf

\fBMessage from <\fP\fIunspecified string\fP\fB>
talk: connection requested by\fP \fIyour_address\fP\fBtalk: respond with: talk\fP \fIyour_address\fP
.fi
.RE
.LP
to the specified \fIaddress\fP. At this point, the recipient of the
message can reply by typing:
.sp
.RS
.nf

\fBtalk\fP \fIyour_address\fP
.fi
.RE
.LP
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 " *" 3
Typing the alert character shall alert the recipient's terminal.
.LP
.IP " *" 3
Typing <control>-L shall cause the sender's screen regions to be refreshed.
.LP
.IP " *" 3
Typing the erase and kill characters shall affect the sender's terminal
in the manner described by the \fBtermios\fP interface
in the Base Definitions volume of IEEE\ Std\ 1003.1-2001, Chapter
11, General
Terminal Interface.
.LP
.IP " *" 3
Typing the interrupt or end-of-file characters shall terminate the
local \fItalk\fP utility. Once the \fItalk\fP session has
been terminated on one side, the other side of the \fItalk\fP session
shall be notified that the \fItalk\fP session has been
terminated and shall be able to do nothing except exit.
.LP
.IP " *" 3
Typing characters from \fILC_CTYPE\fP classifications \fBprint\fP
or \fBspace\fP shall cause those characters to be sent to
the recipient's terminal.
.LP
.IP " *" 3
When and only when the \fIstty\fP \fBiexten\fP local mode is enabled,
the existence and
processing of additional special control characters and multi-byte
or single-byte functions shall be implementation-defined.
.LP
.IP " *" 3
Typing other non-printable characters shall cause implementation-defined
sequences of printable characters to be sent to the
recipient's terminal.
.LP
.LP
Permission to be a recipient of a \fItalk\fP message can be denied
or granted by use of the \fImesg\fP utility. However, a user's privilege
may further constrain the domain of accessibility of
other users' terminals. The \fItalk\fP utility shall fail when the
user lacks the appropriate privileges to perform the requested
action.
.LP
Certain block-mode terminals do not have all the capabilities necessary
to support the simultaneous exchange of messages
required for \fItalk\fP. 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
.LP
None.
.SH OPERANDS
.LP
The following operands shall be supported:
.TP 7
\fIaddress\fP
The recipient of the \fItalk\fP session. One form of \fIaddress\fP
is the <\fIuser\ name\fP>, as returned by the
\fIwho\fP utility. Other address formats and how they are handled
are unspecified.
.TP 7
\fIterminal\fP
If the recipient is logged in more than once, the \fIterminal\fP argument
can be used to indicate the appropriate terminal
name. If \fIterminal\fP is not specified, the \fItalk\fP message shall
be displayed on one or more accessible terminals in use by
the recipient. The format of \fIterminal\fP shall be the same as that
returned by the \fIwho\fP utility.
.sp
.SH STDIN
.LP
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
.LP
None.
.SH ENVIRONMENT VARIABLES
.LP
The following environment variables shall affect the execution of
\fItalk\fP:
.TP 7
\fILANG\fP
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.)
.TP 7
\fILC_ALL\fP
If set to a non-empty string value, override the values of all the
other internationalization variables.
.TP 7
\fILC_CTYPE\fP
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 \fILC_CTYPE\fP
equivalent to the sender's, the results are undefined.
.TP 7
\fILC_MESSAGES\fP
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.
.TP 7
\fINLSPATH\fP
Determine the location of message catalogs for the processing of \fILC_MESSAGES
\&.\fP 
.TP 7
\fITERM\fP
Determine the name of the invoker's terminal type. If this variable
is unset or null, an unspecified default terminal type
shall be used.
.sp
.SH ASYNCHRONOUS EVENTS
.LP
When the \fItalk\fP 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
.LP
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, \fItalk\fP shall exit with a
non-zero status.
.SH STDERR
.LP
None.
.SH OUTPUT FILES
.LP
None.
.SH EXTENDED DESCRIPTION
.LP
None.
.SH EXIT STATUS
.LP
The following exit values shall be returned:
.TP 7
\ 0
Successful completion.
.TP 7
>0
An error occurred or \fItalk\fP was invoked on a terminal incapable
of supporting it.
.sp
.SH CONSEQUENCES OF ERRORS
.LP
Default.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
Because the handling of non-printable, non- <space>s is tied to the
\fIstty\fP
description of \fBiexten\fP, implementation extensions within the
terminal driver can be accessed. For example, some
implementations provide line editing functions with certain control
character sequences.
.SH EXAMPLES
.LP
None.
.SH RATIONALE
.LP
The \fIwrite\fP utility was included in this volume of IEEE\ Std\ 1003.1-2001
since it can be implemented on all terminal types. The \fItalk\fP
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.
.LP
All references to networking abilities (\fItalk\fPing to a user on
another system) were removed as being outside the scope of
this volume of IEEE\ Std\ 1003.1-2001.
.LP
Historical BSD and System V versions of \fItalk\fP 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 \fItalk\fP
specified by this volume of IEEE\ Std\ 1003.1-2001
requires both users to terminate their end of the session explicitly.
.LP
Only messages sent to the terminal of the invoking user can be internationalized
in any way:
.IP " *" 3
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 \fItalk\fP utility. The environment of
the invoking party is irrelevant.
.LP
.IP " *" 3
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).
.LP
.IP " *" 3
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.
.LP
.LP
The text in the STDOUT section reflects the usage of the verb "display"
in this section; some \fItalk\fP 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.
.LP
The format of the terminal name is unspecified, but the descriptions
of \fIps\fP,
\fItalk\fP, \fIwho\fP, and \fIwrite\fP require that
they all use or accept the same format.
.LP
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
.LP
None.
.SH SEE ALSO
.LP
\fImesg\fP , \fIstty\fP , \fIwho\fP , \fIwrite\fP , the Base Definitions
volume of IEEE\ Std\ 1003.1-2001, Chapter 11, General Terminal Interface
.SH 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 .