Regex-fu

Presented on September 10 2020 at the PHPBenelux virtual meetup.
https://www.meetup.com/phpbenelux/events/273015264/
---------------------------------------------------------------
Regular expression, you either hate them or you love them, but do you really know how to harness their power ? Based on the PCRE implementation, this talk will show you how to get the most out of your /^regex(es)?$/, how switches affect your results, how to be less greedy, how to assert your power and let's not forget: when *not* to use regex.
---------------------------------------------------------------

Transcript

1. RegEx Fu Juliette Reinders Folmer @jrf_nl regexcheatsheets.com
3. Wildcards on Steroids
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. Regex Engines Boost DEELX RE2 TRE Pattwo GRETA GLib/ GRegex FREJ RGX QT CL-PPCRE Jakarta Henry Spencer’s regex Oniguruma POSIX ECMAscript PCRE
7. Syntax Overlap
8. PCRE
9. Terminology /[a-z0-9]+/im Regular Expression /[a-z0-9]+/im Delimiters /[a-z0-9]+/im Modifiers
10. A a 1 . ? * + {#} [...] ( ... | ... ) ^ ... $ \w \d \s g m s i  Literals  Wildcard  Quantifiers  Character ranges  Grouping and alternation  Anchors  Shorthand character codes  Modifiers Basic Syntax A a 1 ? * + {#} [...] \w \d \s ( ... | ... ) ^ ... $ g m s i .
11. Tips & Tricks
12. Photo by Scott Liddell 1. If you need a screwdriver, why use a hammer ?
13. 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.
14. 2. Nothing in life is to be feared. It is only to be understood. Marie Curie
15. Allow listing Deny listing Input string Input string ? ?
16. 3. Not all matches are made in heaven... Photo by Petr Kratochvil
17. 4. Only Elephants Remember Everything © Photo by Juliette Reinders Folmer
18. (?:<expr>)
19. Less is the new more 5
20. / / 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 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
21. / / We take one step back, two steps forward
22. <unit>{,m}? <unit>{n,}? <unit>{n,m}? <unit>*? <unit>+? <unit>?? Reluctant Quantifiers
23. 6. Being negative isn't always a bad thing © Photo by Juliette Reinders Folmer
24. [^<chars>]
25. 7. Explore Your Boundaries Photo by Miguel A.C. Domingo
26. Beginning of string Beginning of line Word boundaries End of string End of line
27. 8. The first love is the deepest...
28. /#?([A-F0-9]{6}|[A-F0-9]{3})/i
29. 9. What's this global village people keep talking about ???
30. 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 - -
31. déjà vu [\w ]+ French (fr) déjà vu [\w ]+ English (en)
32. 10. Escape and escape again
33. String delimiter - for prog language Regex delimiter - for regex - for prog language Meta-characters - for regex - for prog language What to Escape ?
34. \[ \] \( \) \| \. \? \* \+ \{ \} \^ \$ \\ \/ Literals [ ] ( ) | . ? * + { } ^ $ \ / (delimiter) Special Meaning Escaping Meta Characters
35. [(] [)] [|] [.] [?][*][+][{][}] [$] [/] Literals [ ] ( ) | . ? * + { } ^ $ \ / (delimiter) Special Meaning Escaping Meta Characters
36. 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(/[[\]\/\\{}()|?+^$*.-]/g, "\\$&"); }
37. Matching a Literal Backslash \\\\ The actual backslash \\\\ Escaping for use in regex \\\\ String escape
38. Modify your behaviour 11
40. Setting: Unsetting: Combined: Apply to subpattern (non-capturing): Inline Modifiers (?i) (?-i) (?im-sx) (?i:subp)
41. Explore
43. /^(( 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
45. [0] – Complete match [1] – Match against sub-pattern 1 [2] – Match against sub-pattern 2 [3] – Match against sub-pattern 3 ... Match Array Photo by Petr Kratochvil
46. (?<name><expr>) (?P>name)
47. [0] – Complete match [firstname] – Match against named sub-pattern firstname [lastname] – Match against named sub-pattern lastname ... Match Array Photo by Petr Kratochvil
48. Image by Gerd Altmann
49. — 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
50. Advanced Features Look around Conditional sub-patterns Recursion Inline comments
51. Thanks! Any questions ? Feedback: https://joind.in/talk/462b2 Slides: https://speakerdeck.com/jrf Course: https://www.pluralsight.com/courses/ regular-expressions-fundamentals