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.1‐2008.

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\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.1‐2008, 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 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 .