.\"	$NetBSD: ttyname.3,v 1.12 2002/10/01 16:48:35 wiz Exp $
.\"
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.\"     @(#)ttyname.3	8.1 (Berkeley) 6/4/93
.\"
.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
.Fd #include \*[Lt]unistd.h\*[Gt]
.Ft char *
.Fn ttyname "int fd"
.Ft int
.Fn isatty "int fd"
.Fd #include \*[Lt]stdlib.h\*[Gt]
.Ft int
.Fn ttyslot
.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 Em 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 and
.Va errno
is set to indicate the error.
.Pp
The
.Fn isatty
function returns 1 if
.Fa fd
is associated with a terminal device; otherwise it returns 0 and
.Va errno
is set to indicate the error.
.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 ERRORS
The
.Fn ttyname
and
.Fn isatty
functions will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa fd
argument is not a valid file descriptor.
.It Bq Er ENOTTY
The
.Fa fd
argument does not refer to a terminal device.
.El
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr ttys 5
.Sh STANDARDS
The
.Fn ttyname
and
.Fn isatty
functions conform to
.St -p1003.1-90 .
.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.