.\" Copyright (c) 1980, 1991 Regents of the University of California.
.\" %sccs.include.redist.man%
.\" @(#)dup.2 6.4 (Berkeley) %G%
.Nd duplicate an existing file descriptor
.Fn dup2 "int oldd" "int newd"
duplicates an existing object descriptor and returns its value to
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
currently not in use by the process.
The object referenced by the descriptor does not distinguish
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.
the value of the new descriptor
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.
is not a valid active descriptor
Too many descriptors are active.