Ruby 2.0.0 introduced several new regular expression features including \K to reset the starting point of the reported match, \R to match any Unicode line break sequence, \X to match an extended grapheme cluster, conditionals with (?(cond)yes|no), character set options like (?u) for Unicode mode, and character properties for Unicode blocks. It also updated its regular expression engine to Onigmo which supports full Unicode regular expressions.

1. Regexp.new('2.0.0')
Ruby 2.0.0 での正規表現の新機能
西山和広
日本Rubyの会
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2. Onigmo
Onigmo (Oniguruma-mod)
NEWS of Ruby 2.0.0 says following only:
Merge Onigmo
https://github.com/k-takata/Onigmo
Details are unknown
詳細不明
1/12

3. New feature (1) K
examples without /K/
"foobar".sub(/(?<=foo)bar/, "") #=> "foo"
"foobar".sub(/(?<=fo*)bar/, "")
# SyntaxError: invalid pattern in look-behind: /(?<=fo*)bar/
examples with /K/
"foobar".sub(/fooKbar/, "") #=> "foo"
"foobar".sub(/fo*Kbar/, "") #=> "foo"
2/12

4. New feature (1) K
Treat the first non-blank character of the line.
examples with /K/
gsub(/^ *K(d+)/) { $1.to_i+1 }
examples without /K/
gsub(/^( *)(d+)/) { "#{$1}#{$2.to_i+1}" }
3/12

5. New feature (2) R
Linebreak
改行文字
Unicode:
(?>x0Dx0A|[x0A-x0Dx{85}x{2028}x{2029}])
Not Unicode:
(?>x0Dx0A|[x0A-x0D])
4/12

6. New feature (3) X
eXtended grapheme cluster
拡張書記素クラスタ
Unicode:
(?>P{M}p{M}*)
Not Unicode:
(?m:.)
5/12

7. Extended grapheme cluster
example:
"u{304B 3099}"[/X/].size #=> 2
U+304B HIRAGANA LETTER KA
U+3099 COMBINING KATAKANA-HIRAGANA
VOICED SOUND MARK
see [UAX #29] for more detail
(Unicode標準附属書29)
6/12

8. New feature (4)
conditional expression:
(?(cond)yes)
(?(cond)yes|no)
example:
" :f o o "[/:(['"])?(?(1)[ws]+1|w+)/]
#=> ":f"
":'f o o'"[/:(['"])?(?(1)[ws]+1|w+)/]
#=> ":'f o o'"
7/12

9. (?adu)
character set option (character range
option)
文字集合オプション (文字範囲オプション)
d: Default (compatible with Ruby 1.9.3)
a: ASCII
u: Unicode
see doc/RE in Onigmo for more detail
8/12

10. (?adu)
examples:
"u{3042}"[/w/] #=> nil
"u{3042}"[/(?a)w/] #=> nil
"u{3042}"[/(?d)w/] #=> nil
"u{3042}"[/(?u)w/] #=> "あ"
/ab/ =~ "au{3042}" #=> nil
/(?a)ab/ =~ "au{3042}" #=> 0
/(?d)ab/ =~ "au{3042}" #=> nil
/(?u)ab/ =~ "au{3042}" #=> nil
9/12

11. (?adu)
(?-a), (?-d), (?-u) do not found
unlike (?-i), (?-m), (?-x)
10/12

12. Character Property
support for Unicode blocks
example:
/p{InHiragana}/ =~ "u3042" #=> 0
/p{InCJKUnifiedIdeographs}/ =~ "u3042" #=> nil
see tool/enc-unicode.rb in Onigmo for
more detail
11/12

13. /z/