Regular Expressions

1. Regular Expressions A Gentle Introduction Rani Nelken *Chinese examples and reference prepared by Chen Shih-Pei

2. Motivation • Powerful language for specifying text patterns • Search, substitute, split, etc. • jEdit support

3. Running example "Exuberance is Beauty." --William Blake 魏良弼，字師說，新建人。嘉靖二年進士。授松陽知縣，召拜刑科給事中。 --明史列傳

4. Simple match "Exuberance is Beauty." --William Blake be 魏良弼，字師說，新建人。嘉靖二年進士。授松陽知縣，召拜刑科給事中。 --明史列傳 字

5. Period "Exuberance is Beauty." --William Blake . 魏良弼，字師說，新建人。嘉靖二年進士。授松陽知縣，召拜刑科給事中。 --明史列傳 . => Period matches any single character

6. Repeating Things "Exuberance is Beauty." --William Blake .* .+ * means repeat zero or more times + means repeat one or more times

7. Repeating Things 魏良弼，字師說，新建人。嘉靖二年進士。授松陽知縣，召拜刑科給事中。--明史列傳 .* .+ * means repeat zero or more times + means repeat one or more times

8. Repeating Things "Exuberance is Beauty." --William Blake l+ "Exuberance is Beauty." --William Blake b+

9. Repeating Things 魏良弼，字師說，新建人。嘉靖二年進士。授松陽知縣，召拜刑科給事中。--明史列傳 -+ 魏良弼，字師說，新建人。嘉靖二年進士。授松陽知縣，召拜刑科給事中。--明史列傳 ，+

10. Repeating Things "Exuberance is Beauty." --William Blake ut+ "Exuberance is Beauty." --William Blake ut*

11. Repeating Things 魏良弼，字師說，新建人。嘉靖二年進士。授松陽知縣，召拜刑科給事中。--明史列傳 知縣+ 魏良弼，字師說，新建人。嘉靖二年進士。授松陽知縣，召拜刑科給事中。--明史列傳 知州*

12. Counting Repetitions "Exuberance is Beauty." --William Blake ut? "Exuberance is Beauty." --William Blake l{2} l{2,3}

13. Counting Repetitions 魏良弼，字師說，新建人。嘉靖二年進士。授松陽知縣，召拜刑科給事中。--明史列傳 知州? 魏良弼，字師說，新建人。嘉靖二年進士。授松陽知縣，召拜刑科給事中。--明史列傳 -{2} -{2,3}

14. Character classes "Exuberance is Beauty." --William Blake \w "Exuberance is Beauty." --William Blake \W "Exuberanceis Beauty." --William Blake \s "Exuberanceis Beauty." --William Blake \S

15. Character classes 魏良弼，字師說，新建人。嘉靖二年進士。 \w 魏良弼，字師說，新建人。嘉靖二年進士。 \W 魏良弼，字師說，新建人。嘉靖二年進士。 \s (no match) 魏良弼，字師說，新建人。嘉靖二年進士。 \S *Note: \w is a more vague class for Chinese characters

16. Character classes "Exuberance is 123." \d [0-9] "Exuberance is 123." \d+ [1-3]+ "Exuberance is 123." [x-y] : character range

17. Character classes Define your own character classes: 魏良弼，字師說，新建人。嘉靖二年進士。 [一二三四五六七八九十] For consecutive Chinese numbers: 正德十二年進士。 [一二三四五六七八九十]+

18. Greedy and Ungreedy Matching "Exuberance is Beauty." --William Blake .+b "Exuberance is Beauty." --William Blake .+B "Exuberance is Beauty." --William Blake .+?B

19. Greedy and Ungreedy Matching "Exuberance is Beauty." --William Blake .+b "Exuberance is Beauty." --William Blake .+B "Exuberance is Beauty." --William Blake .+?B

20. Greedy and Ungreedy Matching 宣宗孝恭皇后孫氏，鄒平人。幼有美色。父忠，永城縣主簿也。誠孝皇后母彭城伯夫人，故永城人，時時入禁中 ，.+人 宣宗孝恭皇后孫氏，鄒平人。幼有美色。父忠，永城縣主簿也。誠孝皇后母彭城伯夫人，故永城人，時時入禁中 ，.+?人

21. Notes on writing your own regex • Multiple styles: the one we’re using is Perl-like • Be careful and precise on what you write: you might match more patterns than you want

22. Regular Expression Syntax Reference (Perl-Style)

23. Characters

24. Character Classes

25. Predefined Character Classes

26. Greedy quantifiers Greedy matching (default): is to match with the longest possible string of characters that matches the pattern

27. Reluctant quantifiers Reluctant matching: to force the expression to find the shortest rather than the longest match

28. Logical operators • Back references