isatty - test whether a file descriptor refers to a terminal
#include <unistd.h>
int isatty(int fd);The isatty() function tests whether fd is an open file descriptor referring to a terminal.
isatty() returns 1 if fd is an open file descriptor referring to a terminal; otherwise 0 is returned, and errno is set to indicate the error.
fd is not a valid file descriptor.
fd refers to a file other than a terminal. On some older kernels, some types of files resulted in the error EINVAL in this case (which is a violation of POSIX, which specifies the error ENOTTY).
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
| isatty() | Thread safety | MT-Safe |
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
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