Should i use regex look back to search this string? - regex

Question

My intended goal:
Need to pull IP address out of a string as i loop through pinging different subnets.
Example of string i will be searching:
>>> pingout = subprocess.getoutput('ping -c' + ' ' + str(1) + ' ' + '10.20.' + str(234.) + str(4))
>>> print(pingout)
PING 10.20.234.04 (10.20.234.4) 56(84) bytes of data.
64 bytes from 10.20.234.4: icmp_seq=1 ttl=64 time=4.01 ms
--- 10.20.234.04 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 4.016/4.016/4.016/0.000 ms
>
I want to use something like this.
match = re.search(r'?<=...........)ping', pingout)
Or this but need to exclude the 'ping' in the result.
match = re.search(r'.............ping',pingout)

Answer 1

Given:
txt='''\
PING 10.20.234.04 (10.20.234.4) 56(84) bytes of data.
64 bytes from 10.20.234.4: icmp_seq=1 ttl=64 time=4.01 ms
--- 10.20.234.04 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 4.016/4.016/4.016/0.000 ms'''
For the first IP address (with 'PING' in the line), you can do:
print(re.search(r'^PING\s*(\d+\.\d+\.\d+\.\d+)', txt, re.M).group(1))
For the second IP address (with 'ping' in the line), you can do:
print(re.search(r'^\D+(\d+\.\d+\.\d+\.\d+)\s*ping', txt, re.M).group(1))
Either case, prints 10.20.234.04

Answer 2

You can use tons of different regexes to extract those IP, I think the closest one to your solutions is:
>>> s
'--- 10.20.234.04 ping statistics ---'
>>> re.findall(".{12}(?= ping)", s)
['10.20.234.04']
But;
>>> import socket
>>> socket.gethostbyname("google.com")
'173.194.39.199'
Would be much better I think(Don't know if it works on subnets tho, but I think they must be the same thing.).

Answer 3

>>> import re
>>> m = re.match(r"PING .+ \((.+)\) .+ bytes of data.", "PING 10.20.234.04 (10.20.234.4) 56(84) bytes of data.")
>>> m
>>> m.groups()
('10.20.234.4',)
If I were going to use the regex repeatedly I would do:
ip_re = re.compile(r"PING .+ \((.+)\) .+ bytes of data.")
m = ip_re.match(pingout)
Note this catches the IP exactly once when ping prints its first line. No need to keep searching. You could extend the regex to catch the amount of data sent or the responses if you need to do so.

Answer 4

Try this regex,
match = re.search(r'.*PING ([0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}).*', PINGOUT)
match.group(1)
Example:
>>> match = re.search(r'.*PING ([0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}).*', "PING 10.20.234.04")
>>> match.group()
'PING 10.20.234.04'
>>> match.group(1)
'10.20.234.04'