Regex-Fu - Speaker Deck

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RegEx-Fu Juliette Reinders Folmer @jrf_nl AMSTERDAM | MAY 8-9, 2018

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Wildcards on Steroids

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Pattern Recognition

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Regex Engines POSIX PCRE ECMAscript Oniguruma Boost DEELX RE2 TRE Pattwo GRETA GLib/ GRegex FREJ RGX QT CL-PPCRE Jakarta Henry Spencer’s regex

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Syntax Overlap

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PCRE

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Terminology /[a-z0-9]+/im Regular Expression /[a-z0-9]+/im Delimiters /[a-z0-9]+/im Modifiers

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Tips & Tricks

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Photo by Scott Liddell 1. If you need a screwdriver, why use a hammer ?

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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.

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2. Nothing in life is to be feared. It is only to be understood. Marie Curie

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Whitelisting Blacklisting Input string Input string ? ?

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3. Not all matches are made in heaven... Photo by Petr Kratochvil

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4. Only Elephants Remember Everything © Photo by Juliette Reinders Folmer

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(?:)

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Less is the new more 5

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/ / 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 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

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/ / We take one step back, two steps forward

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{,m}? {n,}? {n,m}? *? +? ?? Reluctant Quantifiers

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6. Being negative isn't always a bad thing © Photo by Juliette Reinders Folmer

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[^]

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7. Explore Your Boundaries Photo by Miguel A.C. Domingo

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Beginning of string Beginning of line Word boundaries End of string End of line

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8. The first love is the deepest...

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/#?([A-F0-9]{6}|[A-F0-9]{3})/i

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9. What's this global village people keep talking about ???

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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 - -

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déjà vu [\w ]+ French (fr) déjà vu [\w ]+ English (en)

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10. Escape and escape again

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String delimiter - for prog language Regex delimiter - for regex - for prog language Meta-characters - for regex - for prog language What to Escape ?

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\[ \]  \| \. \? \* \+ \{ \} \^ \$ \\ \/ Literals [ ] ( ) | . ? * + { } ^ $ \ / (delimiter) Special Meaning Escaping Meta Characters

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[(] [)] [|] [.] [?][*][+][{][}] [$] [/] Literals [ ] ( ) | . ? * + { } ^ $ \ / (delimiter) Special Meaning Escaping Meta Characters

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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(/[[\]\/\\{}()|?+^$*.-]/g, "\\$&"); }

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Matching a Literal Backslash \\\\ The actual backslash \\\\ Escaping for use in regex \\\\ String escape

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Modify your behaviour 11

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Setting: Unsetting: Combined: Apply to subpattern (non-capturing): Inline Modifiers (?i) (?-i) (?im-sx) (?i:subp)

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Explore

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/^(( 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

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[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

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(?) (?P>name)

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[0] – Complete match [firstname] – Match against named sub-pattern firstname [lastname] – Match against named sub-pattern lastname ... Match Array Photo by Petr Kratochvil

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Image by Gerd Altmann

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— 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

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Advanced Features Look around Conditional sub-patterns Recursion Inline comments

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Thanks! Any questions ? Slides: https://speakerdeck.com/jrf Course: https://www.pluralsight.com/courses/ regular-expressions-fundamentals