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.TH ISATTY "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
.SH PROLOG
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.

.SH NAME
isatty
\(em test for a terminal device
.SH SYNOPSIS
.LP
.nf
#include <unistd.h>
.P
int isatty(int \fIfildes\fP);
.fi
.SH DESCRIPTION
The
\fIisatty\fR()
function shall test whether
.IR fildes ,
an open file descriptor, is associated with a terminal device.
.SH "RETURN VALUE"
The
\fIisatty\fR()
function shall return 1 if
.IR fildes
is associated with a terminal; otherwise, it shall return 0 and may set
.IR errno
to indicate the error.
.SH ERRORS
The
\fIisatty\fR()
function may fail if:
.TP
.BR EBADF
The
.IR fildes
argument is not a valid open file descriptor.
.TP
.BR ENOTTY
The file associated with the
.IR fildes
argument is not a terminal.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
The
\fIisatty\fR()
function does not necessarily indicate that a human being is available
for interaction via
.IR fildes .
It is quite possible that non-terminal devices are connected to the
communications line.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
The Base Definitions volume of POSIX.1\(hy2008,
.IR "\fB<unistd.h>\fP"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

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