RE: AWK - Speaker Deck

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

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Abstract

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Regular Expression Basics AWK Basics

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Regular Expression Basics

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Difficulties of RE Many different implementations Complex Character Sequences

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

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

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

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

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

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

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

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AWK

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Name from famous Human Names Aho Weinberger Kernighan

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

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

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Patterns and Actions pattern { action } pattern { action }

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

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

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

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

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

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Same as NF == 2 && $2 ~ /$.*$/ {print $1}

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