The Language of Regular Expressions. So You Think You Can Speak It? by Rustam Mehmandarov

Transcript

1. The Language of Regular Expressions. So You Think You Can

   Speak It? Rustam Mehmandarov Riga Dev Day

2. The Vision http://xkcd.com/208/

3. …but regex ain’t one! Oh, wait! http://xkcd.com/1171/

4. The Reality

5. None

6. (([0-9]{4})-([0-9]{2})-([0-9]{2})).*\sINFO\s(.*)

7. Log4j Log File

8. .*(INFO|WARN).*

9. .*(INFO|WARN).*

10. (([0-9]{4})-([0-9]{2})-([0-9]{2})).*ERROR(.*)

11. (([0-9]{4})-([0-9]{2})-([0-9]{2})).*ERROR(.*)

12. ^.*192\.168\.0\.6[^9](.*)$

13. ^.*192.168.0.6[^9](.*)

14. ^.*192\.168\.0\.6[^9](.*)$

15. ^.*192\.168\.0\.6[0-9]+[^9](.*)$

16. flavou?r

17. Recap: Quantifiers * + ? {num} {num, num}

18. Recap: Grouping .*(INFO|WARN)(.*) .*(INFO|WARN)(?:.*)

19. (WA) 2014-09-09 WAR FILE WARN [com.example.logging.MyLog]

20. (?=WARN)WA 2014-09-09 WAR FILE WARN [com.example.logging.MyLog]

21. (?=WARN)WA

22. Recap: Lookaround (?=foo) -> Lookahead (?<=foo) -> Lookbehind (?!foo) ->

    Negative Lookahead (?<!foo) -> Negative Lookbehind

23. Lookahead: Example

24. The list

25. Backreferences

26. Backreferences (contd.)

27. Text: OSDC is awesome! HTML: OSDC is <em>awesome</em>! Regex: <.+>

    Result:

28. Text: OSDC is awesome! HTML: OSDC is <em>awesome</em>! Regex: <.+?>

    Result:
29. None

30. http://stackoverflow.com/questions/1732348/ regex-match-open-tags-except-xhtml-self- contained-tags

31. Quantifiers Revisited Greedy: *, +, ?, {num, num} Non-greedy: *?,

    +?, ??, {num, num}?

32. Final Recap • Know your data! – Think what you

    should match – Think what you should not match • Know your flavor • Know your engine (DFA, NFA) – Backtracking • Greediness • Non-capturing parenthesis • Anchors

33. MOAR! EXAMPLES!

34. Matching an IP - 1 Idea 1: ^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$ Result:

35. Matching an IP - 2 Idea 2: ^\d\d\d\.\d\d\d\.\d\d\d\.\d\d\d$ Result:

36. Matching an IP - 3 Idea 3: ^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$ Result:

37. Matching an IP - 4 Idea 4: ^ ([01]?\d\d?|2[0-4]\d|25[0-5])\. ([01]?\d\d?|2[0-4]\d|25[0-5])\.

    ([01]?\d\d?|2[0-4]\d|25[0-5])\. ([01]?\d\d?|2[0-4]\d|25[0-5]) $ Result:

38. Your New Reality! http://xkcd.com/208/

39. Thank you! rmehmandarov rm@computas.com

40. None