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.\"     @(#)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 ttyname ,
.Nm isatty ,
.Nm ttyslot
.Nd get name of associated terminal (tty) from file descriptor
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft char *
.Fn ttyname "int fd"
.Ft int
.Fn isatty "int fd"
.Ft int
.Fn ttyslot void
.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 fd
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.