fix-ipaddr.py

#! /bin/env python3

import sys
import subprocess
import re


'''
default route looks like the following:

    default via 192.168.200.1 dev enp0s20f0u3u4u2 proto dhcp src 192.168.200.54 metric 209
    default via 192.168.1.1 dev wlp1s0 src 192.168.1.125 metric 302
'''
DEFAULT_ROUTE_EXTRACTOR = re.compile(r'^default via [\d.]+ dev ([\w\d]+).+src ([\d./]+)')

'''
ip address line looks like the following:

        inet 192.168.1.125/24 brd 192.168.1.255 scope global wlp1s0
'''
IPADDR_EXTRACTOR = re.compile(r'^\s+inet ([\d./]+)')


def get_default_route():
    routes = subprocess.check_output("ip route list", shell=True).decode('utf8')
    routes = routes.splitlines()
    for route in routes:
        match = DEFAULT_ROUTE_EXTRACTOR.search(route)
        if match:
            return (match[1], match[2])
    return None


def get_unused_ipaddr(interface, ipaddr):
    output = subprocess.check_output(
        'ip addr show {} scope global | grep inet | grep -v {} || true'.format(interface, ipaddr),
        shell=True).decode('utf8')
    match = IPADDR_EXTRACTOR.search(output)
    if not match:
        return None
    return match[1]


if __name__ == '__main__':
    interface, ipaddr = get_default_route()
    unused_ipaddr = get_unused_ipaddr(interface, ipaddr)
    if not unused_ipaddr:
        print('Nothing to do')
        sys.exit(0)
    command = 'ip addr del {} dev {}'.format(unused_ipaddr, interface)
    print(command)
    print(subprocess.check_output('sudo {}'.format(command), shell=True))