Regex-fu

Presented on September 10 2020 at the PHPBenelux virtual meetup.
https://www.meetup.com/phpbenelux/events/273015264/
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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.
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Transcript

1. RegEx Fu
   Juliette Reinders Folmer
   @jrf_nl
   regexcheatsheets.com
   

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3. Wildcards on Steroids
   

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4. Pattern Recognition
   

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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
   

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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
   

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7. Syntax Overlap
   

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8. PCRE
   

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

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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
    .
    

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11. Tips & Tricks
    

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

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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.
    

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14. 2.
    Nothing in life is to
    be feared. It is only
    to be understood.
    Marie Curie
    

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15. Allow listing Deny listing
    Input string Input string
    ? ?
    

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16. 3.
    Not all matches are made in heaven...
    Photo by Petr Kratochvil
    

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17. 4.
    Only
    Elephants
    Remember
    Everything
    © Photo by Juliette Reinders Folmer
    

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18. (?:)
    

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19. Less
    is the
    new more
    5
    

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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
    ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
    

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21. / /
    We take one step back, two steps forward
    

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

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23. 6.
    Being negative
    isn't always a bad
    thing
    © Photo by Juliette Reinders Folmer
    

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24. [^]
    

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25. 7.
    Explore
    Your
    Boundaries
    Photo by Miguel A.C. Domingo
    

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26. Beginning of string
    Beginning of line
    Word boundaries
    End of string
    End of line
    

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27. 8. The first love
    is the deepest...
    

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

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29. 9.
    What's this
    global village
    people
    keep talking
    about ???
    

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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 - -
    

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

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32. 10.
    Escape
    and
    escape again
    

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33. 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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34. \[ \] \( \) \| \. \? \* \+ \{ \} \^ \$ \\ \/
    Literals
    [ ] ( ) | . ? * + { } ^ $ \ / (delimiter)
    Special Meaning
    Escaping Meta Characters
    

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35. [(] [)] [|] [.] [?][*][+][{][}] [$] [/]
    Literals
    [ ] ( ) | . ? * + { } ^ $ \ / (delimiter)
    Special Meaning
    Escaping Meta Characters
    

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

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

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38. Modify
    your
    behaviour
    11
    

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

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41. Explore
    

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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
    

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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
    

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46. (?)
    (?P>name)
    

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47. [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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48. Image by Gerd Altmann
    

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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
    

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50. Advanced Features
    Look around
    Conditional
    sub-patterns
    Recursion
    Inline
    comments
    

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51. Thanks!
    Any questions ?
    Feedback:
    https://joind.in/talk/462b2
    Slides:
    https://speakerdeck.com/jrf
    Course:
    https://www.pluralsight.com/courses/
    regular-expressions-fundamentals
    

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