dup2(3N)                                                 dup2(3N)



NAME
     dup2 - duplicates a descriptor

SYNOPSIS
     dup2(oldd, newd)
     int oldd, newd;

DESCRIPTION
     dup2 causes newd to become a duplicate of oldd.  If newd is
     already in use, the descriptor is first deallocated as if a
     close(2) call had been done first.

     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.  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.

STATUS MESSAGES AND VALUES
     The value -1 is returned if an error occurs in either call.
     The external variable errno indicates the cause of the
     error.

     The dup2 program fails if:

     EBADF
          oldd or newd is not a valid active descriptor

     EMFILE
          Too many descriptors are active.

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



















January 1992                                                    1