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

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

The isatty() function may fail if:

EBADF

The fildes argument is not a valid open file descriptor.

ENOTTY

The fildes argument is not associated with a terminal.

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.

See attributes(5) for descriptions of the following attributes:

ttyname(3C), attributes(5)