regex to get last occurrence of substring between 2 chars

Question

I have a problem because a password is printed out in a log. I can't control the source of the log so my only option is to do a replacement.

I have the following string a = "http://user:password@someurl.ip.com" I want to replace the password with "*****" using a regex

something like

b = re.sub('(?<=:)(.*?)(?=@)', '********', a)

my problem is that I'm matching from the first ":" so I'm replacing "//user:password" instead of "password"

How can I tune my regex to achieve what I want?

Answer 1

You can rule out matching a : and @ using a negated character class:

(?<=:)[^:@]+(?=@)

Regex demo

import re
 
a = "http://user:password@someurl.ip.com"
b = re.sub('(?<=:)[^:@]+(?=@)', '********', a)
print(b)

Output

http://user:********@someurl.ip.com

---

Or perhaps use a bit more specific match using a capture group to match the protocol:

import re
 
a = "http://user:password@someurl.ip.com"
b = re.sub(r"\b(https?://[^:]+:)[^:@]+(?=@)", r"\1********", a)
print(b)