Man page - isatty(3)

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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).

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POSIX.1-2008.

POSIX.1-2001, SVr4, 4.3BSD.