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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
       isatty — test for a terminal device


SYNOPSIS
       #include <unistd.h>

       int isatty(int fildes);


DESCRIPTION
       The  isatty()  function  shall test whether fildes, an open file descriptor, is associated
       with a terminal device.


RETURN VALUE
       The isatty() function shall return 1 if fildes is associated with a  terminal;  otherwise,
       it shall return 0 and may set errno to indicate the error.


ERRORS
       The isatty() function may fail if:

       EBADF  The fildes argument is not a valid open file descriptor.

       ENOTTY The file associated with the fildes argument is not a terminal.

       The following sections are informative.


EXAMPLES
       None.


APPLICATION USAGE
       The  isatty()  function  does not necessarily indicate that a human being is available for
       interaction via fildes.  It is quite possible that non-terminal devices are  connected  to
       the communications line.


RATIONALE
       None.


FUTURE DIRECTIONS
       None.


SEE ALSO
       The Base Definitions volume of POSIX.1‐2017, <unistd.h>


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 .