.\" Copyright (c) 1980 Regents of the University of California.
.\" All rights reserved. The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\" @(#)dup.2 6.3 (Berkeley) %G%
dup, dup2 \- duplicate a descriptor
duplicates an existing object descriptor.
The argument \fIoldd\fP is a small non-negative integer index in
the per-process descriptor table. The value must be less
than the size of the table, which is returned by
The new descriptor returned by the call,
is the lowest numbered descriptor that is
not currently in use by the process.
The object referenced by the descriptor does not distinguish
between references using \fIoldd\fP and \fInewd\fP in any way.
Thus if \fInewd\fP and \fIoldd\fP are duplicate references to an open
calls all move a single pointer into the file,
and append mode, non-blocking I/O and asynchronous I/O options
are shared between the references.
If a separate pointer into the file is desired, a different
object reference to the file must be obtained by issuing an
The close-on-exec flag on the new file descriptor is unset.
In the second form of the call, the value of
desired is specified. If this descriptor is already
in use, the descriptor is first deallocated as if a
call had been done first.
The value \-1 is returned if an error occurs in either call.
indicates the cause of the error.
\fInewd\fP is not a valid active descriptor
Too many descriptors are active.