p = open('/dev/port', 'w')   # open /dev/port in write mode
p.sync = true       # turn buffering off, write to the
        # port as soon as it is requested
p.seek(0x378, IO::SEEK_SET)  # move writing cursor to the parallel
        # port address
p.putc(0b1)      # write 00000001 to it and activate
        # whatever on your I/O board is 
        # attached to the D0 pin
p.seek(0x378, IO::SEEK_SET)  # back again to the port
p.putc(0b0)      # write 00000000 and unset the D0 pin