RE: AWK

Introduction of Regular Expression and AWK on my own

Transcript

1. RE: AWK
   @wtnabe
   Kanazawa.rb meetup #18
   2014-02-15 (Sat) at IT Plaza MUSASHI
   

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2. Abstract
   

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3. Regular Expression Basics
   AWK Basics
   

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4. Regular Expression Basics
   

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5. Difficulties of RE
   Many different implementations
   Complex Character Sequences
   

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6. Rough Classification
   POSIX ( Basic / Extended )
   PCRE (Perl Compatible Regular
   Expression)
   PHP, Apache, GNU Grep, ...
   GNU ( Basic / Extended )
   and more
   

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7. Ignore
   Minor tool's original expressions
   What does grep in your tools mean ?
   

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8. Basic Syntax
   Literal Character
   Meta Character / Escape Sequence
   Character List / Character Class
   Grouping and Back reference
   

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9. Elementary Operators
   .
   * + ?
   |
   () grouping and back reference
   

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10. Elementary Operators
    ^ $ ( \A \z )
    \r \n \s \xXX escape sequence
    [] [^] character list
    

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11. RE Literal and Language
    Syntax
    Such as escape sequence CONFLICT
    with parent language
    Some Languages have RE Literal
    AWK, Perl, Ruby, JavaScript, ...
    

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12. Examples
    /^[0-9]+(-[0-9]+)+$/
    /\s[Kk]anazawa\.rb\s/
    %r{\bhttps?://.*\b}
    

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13. Keep away
    Too Match
    /[0-9-]+/
    Complex one-shot match
    q{[^"'<>]*(?
    :"[^"]*"[^"'<>]*|'[^']*'[^"'<>]*)*(?
    :>|(?=<)|$(?!\n))}; #'}}}}
    cf. Perlメモ
    

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14. AWK
    

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15. Name
    from famous Human Names
    Aho
    Weinberger
    Kernighan
    

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16. Filter-oriented
    Programming Language
    $ awk 'script' srcfile
    $ cat srcfile | awk 'script' > destfile
    $ awk -f script srcfile
    

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17. Basic Syntax
    C-like / Shell-like ( semicolon less )
    Patterns and Actions
    No need to write about stdin and split
    

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18. Patterns and Actions
    pattern {
    action
    }
    pattern {
    action
    }
    

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19. BEGIN and END rule
    BEGIN {
    ...
    }
    END {
    ...
    }
    

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20. Example
    Count a number of gems depending on
    from Gemfile.lock
    

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21. Gemfile.lock
    GEM
    remote: https://rubygems.org/
    specs:
    blankslate (2.1.2.4)
    ...
    PLATFORMS
    ruby
    DEPENDENCIES
    ...
    

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22. BEGIN { counting = 0 }
    /^$/ { counting = 0 }
    counting == 1 && !/:/ {
    print $1
    }
    /^GEM$/ { counting = 1 }
    

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23. $ awk -f script.awk Gemfile.lock | \
    sort | uniq | wc -l
    

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24. Same as
    NF == 2 && $2 ~ /\(.*\)/ {print $1}
    

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25. Notes
    http://www.regular-expressions.info/
    正規表現メモ
    The GNU Awk User's Guide
    The GAWK Manual - Table of Contents
    

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