I want to parse ifconfig to get ip_address, net mask and broadcast. and these are optional fields. If it present, it should return but if not it should return None.

My below pattern works fine but if 'inet6' is not present. if not, then this pattern returns None. I am not sure why it is still trying to match with inet6.

output = """
en0: flags=8863<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
    ether 00:1a:2b:3c:4d:5e
    inet6 fe80::1a2b:3c4d:5e6f:7g8h prefixlen 64 secured scopeid 0x4
    inet 192.168.1.10 netmask 0xffffff00 broadcast 192.168.1.255
"""

# Regex pattern to capture MAC, IPv4 (inet), and IPv6 (inet6) addresses
pattern = repile(r'ether (?P<mac_address>[a-f0-9:]+).*?'
                     r'(?:\s+inet (?P<ip_address>[\d\.]+) '
                     r'netmask (?P<netmask>0x[a-f0-9]+) '                      
                     r'broadcast (?P<broadcast>[.a-f0-9:]+))?.*?')

print(pattern.search(output).groupdict())

I want to parse ifconfig to get ip_address, net mask and broadcast. and these are optional fields. If it present, it should return but if not it should return None.

My below pattern works fine but if 'inet6' is not present. if not, then this pattern returns None. I am not sure why it is still trying to match with inet6.

output = """
en0: flags=8863<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
    ether 00:1a:2b:3c:4d:5e
    inet6 fe80::1a2b:3c4d:5e6f:7g8h prefixlen 64 secured scopeid 0x4
    inet 192.168.1.10 netmask 0xffffff00 broadcast 192.168.1.255
"""

# Regex pattern to capture MAC, IPv4 (inet), and IPv6 (inet6) addresses
pattern = repile(r'ether (?P<mac_address>[a-f0-9:]+).*?'
                     r'(?:\s+inet (?P<ip_address>[\d\.]+) '
                     r'netmask (?P<netmask>0x[a-f0-9]+) '                      
                     r'broadcast (?P<broadcast>[.a-f0-9:]+))?.*?')

print(pattern.search(output).groupdict())

• python-3.x
• regex
• python-re

Share Improve this question Follow asked Nov 17, 2024 at 6:38 premganeshpremganesh 8533 silver badges99 bronze badges 3

• 1 This does not have to be a huge regex. Just read the lines, split by words, and if the first word is "inet" you know the IP is the next word. – Tim Roberts Commented Nov 17, 2024 at 6:41
• That is because the line starting with inet6 is not matched, which you can make optional in this case. See regex101/r/vGUB6I/1 – The fourth bird Commented Nov 17, 2024 at 9:30
• Parsing ifconfig or etc output is a common FAQ; please search before asking. On many modern platforms, it is easy and obvious how to get the results directly in a machine readable form so you don't have to write yet another ad-hoc parser. – tripleee Commented Nov 18, 2024 at 14:00

Add a comment  | 

1 Answer 1

Sorted by: Reset to default 0

Try:

ether (?P<mac_address>[a-f0-9:]+)(?:(?!inet\b)[\w\W])+(?:inet (?P<ip_address>[\d.]+) netmask (?P<netmask>0x[a-f0-9]+) broadcast (?P<broadcast>[.a-f0-9:]+))?

See: regex101

See Python Demo:

import re

output = """
en0: flags=8863<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
    ether 00:1a:2b:3c:4d:5e
    inet6 fe80::1a2b:3c4d:5e6f:7g8h prefixlen 64 secured scopeid 0x4
    inet 192.168.1.10 netmask 0xffffff00 broadcast 192.168.1.255
"""

# Regex pattern to capture MAC, IPv4 (inet), and IPv6 (inet6) addresses
pattern = repile(r'ether (?P<mac_address>[a-f0-9:]+)(?:(?!inet\b)[\w\W])+(?:inet (?P<ip_address>[\d.]+) netmask (?P<netmask>0x[a-f0-9]+) broadcast (?P<broadcast>[.a-f0-9:]+))?')

print(pattern.search(output).groupdict())

---

Explanation

• ether (?P<mac_address>[a-f0-9:]+): your ether part
• (?:: then using a tempered greedy token
  • (?!inet\b): that asserts you match up to exactly inet
  • [\w\W]: any character (including newlines)
• )+:
• (?:inet (?P<ip_address>[\d.]+) netmask (?P<netmask>0x[a-f0-9]+) broadcast (?P<broadcast>[.a-f0-9:]+))?: then your inet, netmask, broadcast part