dirty-helpers/ssh_known_dupes

#!/usr/bin/python3
# Find duplicate keys in ~/.ssh/known_hosts
#
# Of course, we should have been more careful in the first place :)

from __future__ import division, print_function
from collections import defaultdict
import os.path
import re


hostnames_per_key = defaultdict(list)

with open(os.path.expanduser('~/.ssh/known_hosts')) as f:
    for line in f:
        m = re.match('(\S+)\s+(\S+\s+\S+)(.*)?', line)
        if m:
            (hostname, key, cruft) = m.groups()
            hostnames_per_key[key].append(hostname)

for key, hostnames in hostnames_per_key.items():
    if len(hostnames) > 1:
        print(hostnames)