parser = OptionParser(usage=usage_msg)                                                                                                                                            parser.add_option("-1", action="store_true", dest="omit1", help="suppress column 1 (lines unique to FILE1)", default=False)
parser.add_option("-2", action="store_true", dest="omit2", help="suppress column 2 (lines unique to FILE2)", default=False)
parser.add_option("-3", action="store_true", dest="omit3", help="suppress column 3 (lines common to FILE1 and FILE2)", default=False)
parser.add_option("-u", action="store_true", dest="unsort", help="Allows for comm to compare unsorted input(s).", default=False)
options, args = parser.parse_args(sys.argv[1:])

try:
  f = [open(arg, 'r') if arg != '-' else sys.stdin for arg in args]
  if len(f) != NUM_FILES:
    parser.error(usage_msg)
except IOError as err:
  parser.error("I/O error: ".format(errno))