compare.py

import sys, boto
from hashlib import md5

try:
        bucket, key_name, local_name = sys.argv[1:]
except:
        sys.exit("wrong arguments")

c = boto.connect_s3()
b = c.get_bucket(bucket, validate = False )

with open(local_name, "r") as f:
        local_md5  = md5( f.read() ).hexdigest().upper()
key = b.get_key(key_name)
remote_md5 = key.etag.replace('"','').upper()
if local_md5 == remote_md5:
        print "="
else:
        print "<>"