I need to extract the IP address from the following string.
>>> mydns='ec2-54-196-170-182.compute-1.amazonaws.com'
The text to the left of the dot needs to be returned. The following works as expected.
>>> mydns[:18]
'ec2-54-196-170-182'
But it does not work in all cases. For e.g.
mydns='ec2-666-777-888-999.compute-1.amazonaws.com'
>>> mydns[:18]
'ec2-666-777-888-99'
How to I use regular expressions in python?
No need for regex... Just use str.split
mydns.split('.', 1)[0]
Demo:
>>> mydns='ec2-666-777-888-999.compute-1.amazonaws.com'
>>> mydns.split('.', 1)[0]
'ec2-666-777-888-999'
If you wanted to use regex for this:
ec2-([0-9]{1,3})-([0-9]{1,3})-([0-9]{1,3})-([0-9]{1,3}).*
Alternative (EC2 Agnostic):
.*\b([0-9]{1,3})-([0-9]{1,3})-([0-9]{1,3})-([0-9]{1,3}).*
Regular: \1.\2.\3.\4
Reverse: \4.\3.\2.\1
import re
subject = 'ec2-54-196-170-182.compute-1.amazonaws.com'
result = re.sub("ec2-([0-9]{1,3})-([0-9]{1,3})-([0-9]{1,3})-([0-9]{1,3}).*", r"\1.\2.\3.\4", subject)
print result
ec2 is a good idea? The user might possibly have hundreds of similar ip's!!!
aws:region:stuff:morestuff/name/itemsec2 instances and by any chance if there were any other instances then the user is in trouble....*\b([0-9]{1,3})-([0-9]{1,3})-([0-9]{1,3})-([0-9]{1,3}).* can be used instead. I kinda doubt it though. I edited the main post to include the alternative.This regex will match (^[^.]+:
So Try this:
import re
string = "ec2-54-196-170-182.compute-1.amazonaws.com"
ip = re.findall('^[^.]+',string)[0]
print ip
Output:
ec2-54-196-170-182
Best thing is this will match even if the instance was ec2,ec3 so this regex is actually very much similar to the code of @mgilson
^[^.]+ would be a simple enough regex to do the job?