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.\" $OpenBSD: ttyname.3,v 1.15 2005/02/25 03:12:43 cloder Exp $
.\"
.\" 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. 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.
.\"
.Dd June 4, 1993
.Dt TTYNAME 3
.Os
.Sh NAME
.Nm ttyname ,
.Nm ttyname_r ,
.Nm isatty ,
.Nm ttyslot
.Nd get name of associated terminal (tty) from file descriptor
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft char *
.Fn ttyname "int fd"
.Ft int
.Fn ttyname_r "int fd" "char *name" "size_t namesize"
.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 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
and
.Fn ttyname_r
functions get the related device name of a file descriptor for which
.Fn isatty
is true.
The
.Fn ttyname_r
function stores the NUL-terminated
pathname of the terminal associated with
the file descriptor
.Fa fd
in the character array referenced by
.Fa name .
The array is
.Fa namesize
characters long and should have space for the name and the terminating
NUL character.
The maximum length of the terminal name is
.Dv TTY_NAME_MAX .
.Pp
The
.Fn ttyslot
function fetches the current process's control terminal number from the
.Xr ttys 5
file entry.
.Sh RETURN VALUES
The
.Fn ttyname
and
.Fn ttyname_r
functions return the NUL-terminated name if the device is found and
.Fn isatty
is true; otherwise
a 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.
.It Bq Er ERANGE
The value of
.Fa namesize
is smaller than the length of the string to be returned including the
terminating NUL character.
.El
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr ttys 5 ,
.Xr dev_mkdb 8
.Sh HISTORY
The
.Fn isatty ,
.Fn ttyname ,
and
.Fn ttyslot
functions appeared in
.At v7 .
The
.Fn ttyname_r
function appeared in the POSIX Threads Extension (1003.1c-1995).
.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.
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