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.\"     @(#)ttyname.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: src/lib/libc/gen/ttyname.3,v 1.14 2007/01/09 00:27:55 imp Exp $
.\" $DragonFly: src/lib/libc/gen/ttyname.3,v 1.3 2005/11/19 22:32:53 swildner Exp $
.\"
.Dd March 22, 2009
.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 LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft char *
.Fn ttyname "int fd"
.Ft int
.Fn ttyname_r "int fd" "char *buf" "size_t len"
.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 ttyname
function
returns the name stored in a static buffer which will be overwritten
on subsequent calls.
The
.Fn ttyname_r
function
takes a buffer and length as arguments to avoid this problem.
.Pp
The
.Fn ttyslot
function
fetches the current process' control terminal number from the
.Xr ttys 5
file entry.
.Sh RETURN VALUES
The
.Fn isatty
function
returns 1 if the file descriptor refers to a valid terminal
device and 0 otherwise.
.Pp
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.
The
.Fn ttyname_r
function returns 0 if successful.
Otherwise an error number 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 ".Pa /etc/ttys" -compact
.It Pa /dev/\(**
.It Pa /etc/ttys
.El
.Sh ERRORS
The
.Fn ttyname ,
.Fn ttyname_r ,
and
.Fn isatty
functions
may fail and return the following error codes:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa fd
is not a valid open file descriptor.
.It Bq Er ENOTTY
The
.Fa fd
is not associated with a terminal.
.It Bq Er ERANGE
The
.Fa bufsize
argument
is smaller than the length of the string to be returned.
.El
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr ttys 5
.Sh HISTORY
The
.Fn isatty ,
.Fn ttyname ,
and
.Fn ttyslot
functions
appeared in
.At v7 .
The
.Fn ttyname_r
function
appeared in
.Fx 6.0 .