Match similar string in regex

Question

I want to find out if is it possible to match one of two or more similar lines.

Strings to be matched:

Its a string
Its a string
Its a string

Excepted result:

Its a string

Everything I tried just select every line, because they are absolutely similar.

Is it possible to always keep one similar line unmatched?

Answer 1

I'm not 100% sure that this will work for you, but it does what I think you're trying to do.

import re
p = re.compile(r'(^.+$)((.|\n|r)*)^\1$', re.MULTILINE)
result = p.search(string)

repeated_line = result.groups()[0].strip()

You need to specify re.MULTILINE so that it works with capturing ^$ characters.

Here's a quick brake-down of the regex:

(^.+$)          # Matches a full line and captures it into '\1'  
((.|\n|\r)*)    # Matches any number of characters/newlines  
^\1$            # Matches the first capturing group ensuring that the second occurrence fills a line and has it's own line.

There's probably better ways to do this, but this is the first solution I thought up that specifically uses regex.