NAME

isatty — test for a terminal device

SYNOPSIS

#include <unistd.h>

int isatty(int fildes);

DESCRIPTION

The isatty () function shall test whether fildes, an open file descriptor, is associated with a terminal device.

RETURN VALUE

The isatty () function shall return 1 if fildes is associated with a terminal; otherwise, it shall return 0 and may set errno to indicate the error.

ERRORS

The isatty () function may fail if:

[EBADF]

The fildes argument is not a valid open file descriptor.

[ENOTTY]

The file associated with the fildes argument is not a terminal.

The following sections are informative.

EXAMPLES

None.

APPLICATION USAGE

The isatty () function does not necessarily indicate that a human being is available for interaction via fildes. It is quite possible that non-terminal devices are connected to the communications line.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

XBD <unistd.h>

CHANGE HISTORY

First released in Issue 1. Derived from Issue 1 of the SVID.

Issue 6

The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

• The optional setting of errno to indicate an error is added.
• The [EBADF] and [ENOTTY] optional error conditions are added.

Issue 7

SD5-XSH-ERN-100 is applied, correcting the definition of the [ENOTTY] error condition.

End of informative text.