dup(2)                                                     dup(2)



NAME
     dup - duplicates 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
     numbered descriptor which is not currently in use by the
     process.

     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
     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
     and errno is set to indicate the error.

     The dup command fails if:

     EBADF
          The old descriptor is not a valid active descriptor

     EMFILE
          Too many descriptors are active.

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















January 1992                                                    1