ISATTY(3P) POSIX Programmer's Manual ISATTY(3P)

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

isatty — test for a terminal device

#include <unistd.h>
int isatty(int fildes);

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

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.

The isatty() function may fail if:

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

The following sections are informative.


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.



The Base Definitions volume of POSIX.1‐2017, <unistd.h>

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at .

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2017 IEEE/The Open Group