Regular Expression for newbie

1. Regular Expression
101 ~ 1001
cmj / 2019-05 @HST

2. Regular Expression
• RegEx
• PCRE (Perl Compatible Regular Expression)
• Perl and popular

3. Finite-State Machine (FSM)
• Input (Entry state)
• State / Transition
• Accept

4. Example
• Try match aab
• First two a and follow one b
• Accept
• aaaaaabbbbb
• aab
• Reject
• ab
• abb
a
a
bb

5. Grammar I
• . Any character except NEWLINE
• a The character a
• Escapes a special character
• a b f n r t v 0
• YYY
• xXX

6. Grammar II
• a | b The pattern a or pattern b
• a{x, y} x to y number of a
• [abc] One character of a, b or c
• a* Zero or more a
• a+ One or more a
• a? Zero or one a
• reluctant a*? a+?
• greedy a.+

7. Grammar III
• 0-9 Digit from 0 to 9
• d Digit (0 -9)
• D Not digit
• s One whitespace
• S Not whitespace

8. Grammar IV
• (…) Group of pattern
• (?: …) Not-capture group
• (?>…) Atomic group
• (?|…) Duplicate group
• (?P<name>…) Named a group
• (?P=name) Backreference to named group

9. Grammar V
• (?=…) Positive lookahead
• (?!…) Negative lookahead
• (?<=…) Positive lookbehind
• (?<!…) Negative lookbehind

10. Exercise

11. Exercise 1
• HTML tag
• find all <…> format and first appear word
• <(w+).*?>

12. Exercise 2
• Birthday validator
• Date format
• MM-DD-YYYY d{2}-d{2}-d{4}
https://en.wikipedia.org/wiki/Date_format_by_country

13. Exercise 2
• Birthday validator
• Date format
• MM-DD-YYYY d{2}-d{2}-d{4}
• ^(?:(?:(?:0?[13578]|1[02])(/|-|.)31)1|(?:(?:0?[1,3-9]|1[0-2])
(/|-|.)(?:29|30)2))(?:(?:1[6-9]|[2-9]d)?d{2})$|^(?:0?2(/|-|
.)293(?:(?:(?:1[6-9]|[2-9]d)?(?:0[48]|[2468][048]|[13579]
[26])|(?:(?:16|[2468][048]|[3579][26])00))))$|^(?:(?:0?[1-9])|(?:
1[0-2]))(/|-|.)(?:0?[1-9]|1d|2[0-8])4(?:(?:1[6-9]|[2-9]d)?
d{2})$
https://stackoverflow.com/questions/51224/regular-expression-to-match-valid-dates/8768241#8768241

14. Exercise 3
• ETH address
• 0x prefix with extra 40 characters
• 0x[a-zA-Z0-9]{40}
• BTC address
• ^[13][a-km-zA-Hj_Np-Z1-9]{25,34}
https://stackoverflow.com/questions/21683680/regex-to-match-bitcoin-addresses

15. Exercise 4
• Any imgur link
• https?://i.imgur.com/.*.(png|jpg|gif)
• https?://i.imgur.com/.*?.(png|jpg|gif)

16. Exercise 5
• Difference between
• ab(ab)
• (?<=ab)ab

17. Exercise 5
• Difference between
• ab(ab)
• (?<=ab)ab

18. Exercise 5
• Difference between
• ab(ab)
• (?<=ab)ab

19. No Q&A