#!/usr/bin/env python

import optparse

def main():
	parser = optparse.OptionParser(usage="%prog file1 file2")
	options, args = parser.parse_args()
	sets = []
	for fname in args:
		sets.append(set(open(fname, "r").readlines()))
	print "common lines in both files:"
	for line in sets[0] & sets[1]:
		print repr(line)

if __name__ == "__main__":
	main()