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.\"     @(#)ttyname.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD$
.\"
.Dd July 18, 2014
.Dt TTYNAME 3
.Os
.Sh NAME
.Nm ttyname ,
.Nm ttyname_r ,
.Nm isatty
.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"
.Sh DESCRIPTION
These functions operate on file descriptors for terminal type devices.
.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.
.Sh RETURN VALUES
The
.Fn isatty
function returns 1 if
.Fa fd
refers to a terminal type device;
otherwise, it returns 0 and may set
.Va errno
to indicate the error.
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.
.Sh ERRORS
These functions may 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 file associated with
.Fa fd
is not a terminal.
.El
.Pp
Additionally,
.Fn ttyname_r
may fail if:
.Bl -tag -width Er
.It Bq Er ERANGE
The
.Fa bufsize
argument
is smaller than the length of the string to be returned.
.El
.Sh SEE ALSO
.Xr fdevname 3 ,
.Xr ptsname 3 ,
.Xr tcgetattr 3 ,
.Xr tty 4
.Sh HISTORY
The
.Fn isatty
and
.Fn ttyname
functions
appeared in
.At v7 .
The
.Fn ttyname_r
function
appeared in
.Fx 6.0 .