NAME
dup, dup2 - duplicate a descriptor

SYNOPSIS
newd = dup(oldd)
int newd, oldd;

dup2(oldd, newd)
int oldd, newd;

DESCRIPTION
Dup duplicates an existing object descriptor. The argument oldd 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 getdtablesize(2). The new descriptor returned by the
call, newd, 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 oldd and newd in any way. Thus if newd
and oldd are duplicate references to an open file, read(2),
write(2) and lseek(2) 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 additional open(2) call. The
close-on-exec flag on the new file descriptor is unset.

In the second form of the call, the value of newd desired is
specified. If this descriptor is already in use, the descriptor is
first deallocated as if a close(2) call had been done first.

RETURN VALUE
The value -1 is returned if an error occurs in either call. The
external variable errno indicates the cause of the error.

ERRORS
Dup and dup2 fail if:

[EBADF] Oldd or newd is not a valid active descriptor

[EMFILE] Too many descriptors are active.

SEE ALSO
accept(2), open(2), close(2), fcntl(2), pipe(2), socket(2),
socketpair(2), getdtablesize(2)