/sys$common/syshlp/helplib.hlb CC, Run-time functions, dup  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Allocates a new file descriptor that refers to a file specified by
  a file descriptor returned by open, creat, or pipe.

  Syntax:

       #include <unistd.h>

       int dup(int file_desc1);