This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       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).

       Default.

       Default.

       Thefollowingsectionsareinformative.

       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(1POSIX)

       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.

       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, Section8.2, InternationalizationVariables 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.

       None.

       The following exit values shall be returned:

        0    Standard input is a terminal.

        1    Standard input is not a terminal.

       >1    An error occurred.

       None.

       None.

       None.

       tty — return user's terminal name

       None.

       The  tty  utility  shall  conform  to  the Base Definitions volume of POSIX.1‐2017, Section12.2, UtilitySyntaxGuidelines.

       None.

       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.

       None.

       The  Base  Definitions  volume  of  POSIX.1‐2017, Chapter8, EnvironmentVariables, Section12.2, UtilitySyntaxGuidelines

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

       The standard error shall be used only for diagnostic messages.

       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.

       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", <terminalname>

       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"

       tty