isatty - test for terminal device

Syntax	#include <unistd.h> int isatty(int fildes);
Description	isatty() tests whether the file descriptor specified with fildes is associated with a terminal device.
Return val.	1 0	if successful. fildes is associated with a terminal. if an error occurs. errno is set to indicate the error.
Errors	isatty() will fail if:
	EBADF	fildes is not a valid file descriptor.
	ENOTTY	fildes is not associated with a terminal.
See also	unistd.h.