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.\" Copyright 2008, Linux Foundation, written by Michael Kerrisk
.\" <mtk.manpages@gmail.com>
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein. The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.TH ISATTY 3 2008-12-03 "Linux" "Linux Programmer's Manual"
.SH NAME
isatty \- test whether a file descriptor refers to a terminal
.SH SYNOPSIS
.nf
.B #include <unistd.h>
.sp
.BI "int isatty(int " fd );
.fi
.SH DESCRIPTION
The
.BR isatty ()
function tests whether
.I fd
is an open file descriptor referring to a terminal.
.SH RETURN VALUE
.BR isatty ()
returns 1 if
.I fd
is an open file descriptor referring to a terminal;
otherwise 0 is returned, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EBADF
.I fd
is not a valid file descriptor.
.TP
.B EINVAL
.I fd
refers to a file other than a terminal.
POSIX.1-2001 specifies the error
.BR ENOTTY
.\" FIXME File a bug for this?
for this case.
.SH "CONFORMING TO"
SVr4, 4.3BSD, POSIX.1-2001.
.SH "SEE ALSO"
.BR fstat (2),
.BR ttyname (3)
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