Regex Fundamentals - Speaker Deck

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Regular Expression Fundamentals Juliette Reinders Folmer @jrf_nl regexcheatsheets.com

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pluralsight.com

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Wildcards on Steriods

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Pattern Recognition

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Serial numbers Barcodes Flight numbers CSV files Log files Email headers Twitter handles Facebook username Skype usernames MD5 hash Sentences Good passwords Isbn numbers HTML code Html tags Html attributes CSS code Urls Email addresses File names File extensions Directory paths Postal codes Telephone numbers Number plates Credit card numbers Bank account numbers Mathematical formulas Elements from the periodical table Patterns in text strings

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Whitelisting Blacklisting Input string Input string ? ?

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Typical Uses for Regular Expressions Search (and replace) String parsing Data mapping Syntax highlighting Data scraping Input validation

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(Sys-)Admins File system Server directives Data Professionals Query data Developers Working with strings Users of Regular Expressions

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How It Works

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Subject String Subject

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How It Works Pattern Regex Subject Function Engine Result

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What are the matches ? How many matches have been found ? Does it match ? Result Types

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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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Still with me ?

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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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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

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The Pattern # AB 12 34

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Visualization of the Pattern

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

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

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(?:)

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4. Being negative isn't always a bad thing © 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. 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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7. The first love is the deepest...

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

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8. 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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9. Escape and escape again

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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 10

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

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Advanced Features Look around Named sub-matches 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