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.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 null-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 null-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.