# tty

## 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.
    


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