Regex Tips & Tricks

Presented on December 6th, 2017 at the Confoo conference, Vancouver, Canada.
https://confoo.ca/en/yvr2017/
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No matter whether you develop in PHP, Javascript, Ruby, Python or even HTML5, knowing how to write Regular Expressions is an essential skill for any developer.
While many consider regexes to be black magic, used appropriately they're an awesome power-tool in your tool-belt.
This talk will show you how to build effective regular expressions, introduce you to some of the more advanced features and teach you some useful tips and tricks.
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Links:
https://www.pluralsight.com/courses/regular-expressions-fundamentals

Transcript

1. RegEx Tips & Tricks Juliette Reinders Folmer @jrf_nl regexcheatsheets.com
3. Wildcards on Steriods
4. Pattern Recognition
5. Regex Engines POSIX PCRE ECMAscript Oniguruma Boost DEELX RE2 TRE Pattwo GRETA GLib/ GRegex FREJ RGX QT CL-PPCRE Jakarta Henry Spencer’s regex
6. Syntax Overlap
7. Tips & Tricks
8. Terminology /[a-z0-9]+/im Regular Expression /[a-z0-9]+/im Delimiters /[a-z0-9]+/im Modifiers
9. Photo by Scott Liddell 1. If you need a screwdriver, why use a hammer ?
10. Jamie Zawinski, August 1997 alt.religion.emacs Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems.
11. 2. Nothing in life is to be feared. It is only to be understood. Marie Curie
12. Whitelisting Blacklisting Input string Input string ? ?
13. 3. Not all matches are made in heaven... Photo by Petr Kratochvil
14. 4. Only Elephants Remember Everything © Photo by Juliette Reinders Folmer
15. (?:<expr>)
16. Less is the new more 5
17. / / o on one one. one.* one.*s one.*s. one.*s.? one.*s.?t one.*s.?t [a-z] one.*s.?t[a-z]+ one.*s.?t[a-z]+p = space one.*s.?t[a-z]+p one.*s.?t[a-z]+p . one.*s.?t[a-z]+p . {2,} one.*s.?t[a-z]+p .{2,}, one.*s.?t[a-z]+p .{2,}, We take one step forward, two steps back ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
18. / / We take one step back, two steps forward
19. <unit>{,m}? <unit>{n,}? <unit>{n,m}? <unit>*? <unit>+? <unit>?? Reluctant Quantifiers
20. 6. Being negative isn't always a bad thing © Photo by Juliette Reinders Folmer
21. [^<chars>]
22. 7. Explore Your Boundaries Photo by Miguel A.C. Domingo
23. Beginning of string Beginning of line Word boundaries End of string End of line
24. 8. The first love is the deepest...
25. /#?([A-F0-9]{6}|[A-F0-9]{3})/i
26. 9. What's this global village people keep talking about ???
27. Character classes PCRE POSIX [0-9] [^0-9] \d \D [[:digit:]] [^[:digit:]] [A-Za-z0-9_] [^A-Za-z0-9_] \w \W [[:word:]] [^[:word:]] [\t\f\r\n \v] [^\t\f\r\n \v] \s \S [[:space:]] [^[:space:]] [\t\f ] [^\t\f ] \h \H [[:blank:]] [^[:blank:]] [\r\n] [^\r\n] \v \V - -
28. déjà vu [\w ]+ French (fr) déjà vu [\w ]+ English (en)
29. 10. Escape and escape again
30. String delimiter - for prog language Regex delimiter - for regex - for prog language Meta-characters - for regex - for prog language What to Escape ?
31. \[ \] \( \) \| \. \? \* \+ \{ \} \^ \$ \\ \/ Literals [ ] ( ) | . ? * + { } ^ $ \ / (delimiter) Special Meaning Escaping Meta Characters
32. [(] [)] [|] [.] [?][*][+][{][}] [$] [/] Literals [ ] ( ) | . ? * + { } ^ $ \ / (delimiter) Special Meaning Escaping Meta Characters
33. Java String.quote() quoteReplacement() PHP preg_quote() Matlab regexptranslate() Python re.escape() Objective-C escapedTemplateForString() escapedPatternForString() Ruby Regexp.escape() Regexp.quote() Escaping Arbitrary Strings // Javascript: function escapeInputString( str ) { return str.replace(/[[\]\/\\{}()|?+^$*.-]/g, "\\$&"); }
34. Matching a Literal Backslash \\\\ The actual backslash \\\\ Escaping for use in regex \\\\ String escape
35. Modify your behaviour 11
37. Setting: Unsetting: Combined: Apply to subpattern (non-capturing): Inline Modifiers (?i) (?-i) (?im-sx) (?i:subp)
38. Explore
40. /^(( 25[0-5]| # Match 250-255 range 2[0-4][0-9]| # Match 200-249 range [01]?[0-9]{1,2} # Match 0-199 range )\.){3} # Repeat 3 times with period (25[0-5]|2[0-4][0-9]|[01]?[0-9]{1,2}) # and once without $/x
41. Advanced Features Look around Named sub-matches Conditional sub-patterns Recursion Inline comments
42. Image by Gerd Altmann
43. — Richard Feynman Know how to solve every problem that has been solved. What I cannot create, I do not understand. Photo by Gleick, J. Genius. p. 310f
44. Thanks! Any questions ? Slides: https://speakerdeck.com/jrf Course: https://www.pluralsight.com/courses/ regular-expressions-fundamentals