isatty

Section: C Library Functions (3)
Updated: 2023-10-31
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NAME

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.1-2008.

POSIX.1-2001, SVr4, 4.3BSD.