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
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 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
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,
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 http://www.opengroup.org/unix/online.html .
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