Разбить файл по доменным зонам

out = dict()
for line in readlines:
    part = line.rpartition('.')
    if part[2]:
        l = out.setdefault(part[2], list())
        l.append(line)

import sys

if __name__ == '__main__':
    if len(sys.argv) != 2:
        print('Usage: {0} <path>'.format(sys.argv[0]))
        sys.exit(1)
    files = {}
    try:
        with open(sys.argv[1]) as source:
            for line in source:
                zone = line.strip().rpartition('.')[-1]
                if zone not in files:
                    files[zone] = open('{0}.txt'.format(zone), 'w')
                files[zone].write(line)
    finally:
        for f in files.values():
            f.close()

awk -F'.' '{print $0 > $NF}' input.txt

awk -F'.' '{print $0 > $NF".txt"}' input.txt