The isatty() function shall test whether fildes, an open
file descriptor, is associated with a terminal
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.
The isatty() function may fail if:
The fildes argument is not a valid open file descriptor.
The fildes argument is not associated with a terminal.
The following sections are informative.
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
The Base Definitions volume of IEEE Std 1003.1-2001, <unistd.h>
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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