dup(2)                                                     dup(2)



     NAME
          dup - duplicate a descriptor

     SYNOPSIS
          int dup(oldd)
          int oldd;

     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(2N).
          The new descriptor returned by the call is the lowest num-
          bered descriptor which is not currently in use by the pro-
          cess.

          The object referenced by the descriptor does not distinguish
          between references using the old and new descriptor in any
          way.  Thus if the old and new descriptor are duplicate
          references to an open file, read(2), write(2), and lseek(2)
          calls all move a single pointer into the file.  If a
          separate pointer into the file is desired, a different ob-
          ject reference to the file must be obtained by issuing an
          additional open(2) call.

     RETURN VALUE
          The value -1 is returned if an error occurs in either call
          and errno is set to indicate the error.

     ERRORS
          dup fails if:

          [EBADF]   The old descriptor is not a valid active descrip-
                    tor

          [EMFILE]  Too many descriptors are active.

     SEE ALSO
          accept(2N), open(2), close(2), getdtablesize(2N), pipe(2),
          socket(2N), dup2(3N).















     April, 1990                                                     1