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 $NetBSD: ttyname.3,v 1.24 2012/06/03 21:42:46 joerg Exp $

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 @(#)ttyname.3 8.1 (Berkeley) 6/4/93

.Dd June 1, 2012
.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
n 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"
n stdlib.h .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

a /dev
and named

a /dev/tty Ns Em xx
and for which an entry exists in the initialization file

a /etc/ttys
(see
.Xr ttys 5 ) ,
or for pseudo-terminal devices created in ptyfs and named

a /dev/pts/ Ns Em n .

p
The
.Fn isatty
function
determines if the file descriptor
.Fa fd
refers to a valid terminal type device.

p
The
.Fn ttyname
function gets the related device name of a file descriptor for
which
.Fn isatty
is true.
The
.Fn ttyname_r
is the reentrant version of the above, and it places the results in
.Fa buf .
If there is not enough space to place the results (indicated by
.Fa len ) ,
then it returns an error.

p
The
.Fn ttyslot
function
fetches the current process' control terminal number from the
.Xr ttys 5
file entry.
If the terminal is a pseudo-terminal, and there is no special entry
in the
.Xr ttys 5
file for it, the slot number returned is 1 + (last slot number) +
minor(tty).
This will return a consistent and unique number for each pseudo-terminal
device without requiring one to enumerate all of them in
.Xr ttys 5 .
.Sh IMPLEMENTATION NOTES
As an optimisation, these functions attempt to obtain information about
all devices from the

a /var/run/dev.cdb
database, if it exists.
If the database exists but is out of date, then these functions
may produce incorrect results.
The database should be updated using the
.Xr dev_mkdb 8
command.
.Sh RETURN VALUES
The
.Fn ttyname
function returns the NUL-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.

p
The
.Fn ttyname_r
functions returns 0 on success and an error code on failure.

p
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.

p
The
.Fn ttyslot
function
returns the unit number of the device file if found; otherwise
the value zero is returned.
.Sh FILES
l -tag -width /etc/ttys -compact t Pa /dev/\(** t Pa /etc/ttys .El
.Sh ERRORS
The
.Fn ttyname ,
.Fn ttyname_r ,
and
.Fn isatty
functions will fail if:
l -tag -width Er t Bq Er EBADF The
.Fa fd
argument is not a valid file descriptor.
t Bq Er ENOTTY The
.Fa fd
argument does not refer to a terminal device.
.El

p
The
.Fn ttyname_r
function will also fail if:
l -tag -width Er t Bq Er ENOENT The terminal device is not found.
This can happen if the device node has been removed after it was opened.
t Bq Er ERANGE The buffer provided is not large enough to fit the result.
.El
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr ttys 5 ,
.Xr dev_mkdb 8
.Sh STANDARDS
The
.Fn ttyname
and
.Fn isatty
functions conform to
.St -p1003.1-90 .
.Sh HISTORY
.Fn isatty ,
.Fn ttyname ,
and
.Fn ttyslot
functions appeared in
.At v7 .
 Use of the .Pa /var/run/dev.cdb file was added in netBSD 6.0.
.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.