posix man page for tty

TTY(1P) 						     POSIX Programmer's Manual							   TTY(1P)

PROLOG
       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME
       tty -- return user's terminal name

SYNOPSIS
       tty

DESCRIPTION
       The tty utility shall write to the standard output the name of the terminal that is open as standard input. The name that is used shall	be
       equivalent to the string that would be returned by the ttyname() function defined in the System Interfaces volume of POSIX.1-2008.

OPTIONS
       The tty utility shall conform to the Base Definitions volume of POSIX.1-2008, Section 12.2, Utility Syntax Guidelines.

OPERANDS
       None.

STDIN
       While  no  input is read from standard input, standard input shall be examined to determine whether or not it is a terminal, and, if so, to
       determine the name of the terminal.

INPUT FILES
       None.

ENVIRONMENT VARIABLES
       The following environment variables shall affect the execution of tty:

       LANG	 Provide a default value for the internationalization variables that are unset or  null.  (See	the  Base  Definitions	volume	of
		 POSIX.1-2008,	Section 8.2, Internationalization 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 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).

       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.

ASYNCHRONOUS EVENTS
       Default.

STDOUT
       If standard input is a terminal device, a pathname of the terminal as specified by the ttyname() function defined in the System	Interfaces
       volume of POSIX.1-2008 shall be written in the following format:

	   "%s
", <terminal name>

       Otherwise,  a  message shall be written indicating that standard input is not connected to a terminal. In the POSIX locale, the tty utility
       shall use the format:

	   "not a tty
"

STDERR
       The standard error shall be used only for diagnostic messages.

OUTPUT FILES
       None.

EXTENDED DESCRIPTION
       None.

EXIT STATUS
       The following exit values shall be returned:

	0    Standard input is a terminal.

	1    Standard input is not a terminal.

       >1    An error occurred.

CONSEQUENCES OF ERRORS
       Default.

       The following sections are informative.

APPLICATION USAGE
       This utility checks the status of the file open as standard input against that of an implementation-defined set of files.  It  is  possible
       that  no  match	can be found, or that the match found need not be the same file as that which was opened for standard input (although they
       are the same device).

EXAMPLES
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       The Base Definitions volume of POSIX.1-2008, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines

       The System Interfaces volume of POSIX.1-2008, isatty(), ttyname()

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy  --	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 Stan-
       dard 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 .

IEEE
/The Open Group						       2013								   TTY(1P)