import sys

file = open(sys.argv[1])

chunksize = 256

pos = -(chunksize + 7)

while 1:
	file.seek(pos, 2)
	stuffs = file.read(chunksize + 7)
	print pos
	if "ustar  " in stuffs:
		usloc = stuffs.find("ustar  ") + (file.tell() - chunksize - 7)
		headloc = usloc - 257
		print "found ustar at %s, last header starts at %s - chop to %s" % (usloc, headloc, headloc-1)
		print "command is: head -c +%s %s | tar xv" % (headloc-1, sys.argv[1])
		sys.exit(0)
	pos -= chunksize