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 corresponding
       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.1-2017.

OPTIONS
       The tty utility shall conform to the Base Definitions volume of
       POSIX.1-2017, 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.1-2017, 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.1-2017 shall be written in the following format:


           "%s\n", <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\n"

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.1-2017, Chapter 8, Environment
       Variables, Section 12.2, Utility Syntax Guidelines

       The System Interfaces volume of POSIX.1-2017, isatty(), ttyname()

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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                  2017                              TTY(1P)