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
2. Abstract
3. Regular Expression Basics AWK Basics
4. Regular Expression Basics
5. Difficulties of RE Many different implementations Complex Character Sequences
6. Rough Classification POSIX ( Basic / Extended ) PCRE (Perl Compatible Regular Expression) PHP, Apache, GNU Grep, ... GNU ( Basic / Extended ) and more
7. Ignore Minor tool's original expressions What does grep in your tools mean ?
8. Basic Syntax Literal Character Meta Character / Escape Sequence Character List / Character Class Grouping and Back reference
9. Elementary Operators . * + ? | () grouping and back reference
10. Elementary Operators ^ $ ( \A \z ) \r \n \s \xXX escape sequence [] [^] character list
11. RE Literal and Language Syntax Such as escape sequence CONFLICT with parent language Some Languages have RE Literal AWK, Perl, Ruby, JavaScript, ...
12. Examples /^[0-9]+(-[0-9]+)+$/ /\s[Kk]anazawa\.rb\s/ %r{\bhttps?://.*\b}
13. Keep away Too Match /[0-9-]+/ Complex one-shot match q{[^"'<>]*(? :"[^"]*"[^"'<>]*|'[^']*'[^"'<>]*)*(? :>|(?=<)|$(?!\n))}; #'}}}} cf. Perlメモ
14. AWK
15. Name from famous Human Names Aho Weinberger Kernighan
16. Filter-oriented Programming Language $ awk 'script' srcfile $ cat srcfile | awk 'script' > destfile $ awk -f script srcfile
17. Basic Syntax C-like / Shell-like ( semicolon less ) Patterns and Actions No need to write about stdin and split
18. Patterns and Actions pattern { action } pattern { action }
19. BEGIN and END rule BEGIN { ... } END { ... }
20. Example Count a number of gems depending on from Gemfile.lock
21. Gemfile.lock GEM remote: https://rubygems.org/ specs: blankslate (2.1.2.4) ... PLATFORMS ruby DEPENDENCIES ...
22. BEGIN { counting = 0 } /^$/ { counting = 0 } counting == 1 && !/:/ { print $1 } /^GEM$/ { counting = 1 }
23. $ awk -f script.awk Gemfile.lock | \ sort | uniq | wc -l
24. Same as NF == 2 && $2 ~ /\(.*\)/ {print $1}
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