.\" Copyright (c) 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)ttyname.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: src/lib/libc/gen/ttyname.3,v 1.10 2002/12/18 13:33:02 ru Exp $
.\"
.Dd June 4, 1993
.Dt TTYNAME 3
.Os
.Sh NAME
.Nm isatty ,
.Nm ttyname ,
.Nm ttyslot
.Nd get name of associated terminal (tty) from file descriptor
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fo isatty
.Fa "int fildes"
.Fc
.Ft char *
.Fo ttyname
.Fa "int fildes"
.Fc
.Ft int
.Fo ttyslot
.Fa void
.Fc
.Sh DESCRIPTION
These functions operate on the system file descriptors for terminal
type devices.
These descriptors are not related to the standard
.Tn I/O
.Dv FILE
typedef, but refer to the special device files found in
.Pa /dev
and named
.Pa /dev/tty Ns Ar xx
and for which an entry exists
in the initialization file
.Pa /etc/ttys .
(See
.Xr ttys 5 . )
.Pp
The
.Fn isatty
function
determines if the file descriptor
.Fa fildes
refers to a valid
terminal type device.
.Pp
The
.Fn ttyname
function
gets the related device name of
a file descriptor for which
.Fn isatty
is true.
.Pp
The
.Fn ttyslot
function
fetches the current process' control terminal number from the
.Xr ttys 5
file entry.
.Sh RETURN VALUES
The
.Fn ttyname
function
returns the null terminated name if the device is found and
.Fn isatty
is true; otherwise, a
.Dv NULL
pointer is returned.
.Pp
The
.Fn ttyslot
function returns the unit number of the device file if found;
otherwise, the value zero is returned.
.Sh FILES
.Bl -tag -width /etc/ttys -compact
.It Pa /dev/\(**
.It Pa /etc/ttys
.El
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr ttys 5
.Sh HISTORY
A
.Fn isatty ,
.Fn ttyname ,
and
.Fn ttyslot
function
appeared in
.At v7 .
.Sh BUGS
The
.Fn ttyname
function leaves its result in an internal static object and returns
a pointer to that object.
Subsequent calls to
.Fn ttyname
will modify the same object.