isatty - test whether a file descriptor refers to a terminal
Standard C library (libc, -lc)
#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.
- EBADF
- fd is not a valid file descriptor.
- ENOTTY
- 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, SVr4, 4.3BSD.