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Regular Expressions
Oniguruma Regular Expressions Version 5.5.1 2006/12/21
This section covers the Ruby regular expression syntax. For information on Perl regular expression syntax, see your Perl documentation or http://www.perl.com/doc/manual/html/pod/perlre.html.
1. Syntax elements
\ escape (enable or disable meta character meaning)
| alternation
(...) group<
[...] character class
2. Characters
\t horizontal tab (0x09)
\v vertical tab (0x0B)
\n newline 0x0A)
\r return (0x0D)
\b back space (0x08)
\f form feed (0x0C)
\a bell (0x07)
\e escape (0x1B)
\nnn octal char (encoded byte value)
\xHH hexadecimal char (encoded byte value)
\x{7HHHHHHH} wide hexadecimal char (character code point value)
\cx control char (character code point value)
\C-x control char (character code point value)
\M-x meta (x|0x80) (character code point value)
\M-\C-x meta control char (character code point value)
(* \b is effective in character class [...] only)
3. Character types
any character (except newline)
\w word character
Not Unicode:
alphanumeric, "_" and multibyte char.
Unicode:
General_Category -- (Letter|Mark|Number|Connector_Punctuation)
\W non word char
\s whitespace char
Not Unicode:
\t, \n, \v, \f, \r, \x20
Unicode:
0009, 000A, 000B, 000C, 000D, 0085(NEL),
General_Category -- Line_Separator
-- Paragraph_Separator
-- Space_Separator
\S non whitespace char
\d decimal digit char
Unicode: General_Category -- Decimal_Number
\D non decimal digit char
\h hexadecimal digit char [0-9a-fA-F]
\H non hexadecimal digit char
Character Property
* \p{property-name}
* \p{^property-name}(negative)
* \P{property-name}(negative)
property-name:
+ works on all encodings
Alnum, Alpha, Blank, Cntrl, Digit, Graph, Lower, Print, Punct, Space, Upper, XDigit, Word, ASCII,
4. Quantifier
greedy
? 1 or 0 times
* 0 or more times
+ 1 or more times
{n,m} at least n but not more than m times
{n,} at least n times
{,n} at least 0 but not more than n times ({0,n})
{n} n times
reluctant
?? 1 or 0 times
*? 0 or more times
+? 1 or more times
{n,m}? at least n but not more than m times
{n,}? at least n times
{,n}? at least 0 but not more than n times (== {0,n}?)
possessive (greedy and does not backtrack after repeated)
?+ 1 or 0 times
*+ 0 or more times
++ 1 or more times
({n,m}+, {n,}+, {n}+ are possessive op. in ONIG_SYNTAX_JAVA only)
ex. /a*+/ === /(?>a*)/
5. Anchors
^ beginning of the line
$ end of the line
\b word boundary
\B not word boundary
\A beginning of string
\Z end of string, or before newline at the end
\z end of string
\G matching start position (*)
6. Character class
^... negative class (lowest precedence operator)
x-y range from x to y
[...] set (character class in character class)
..&&.. intersection (low precedence at the next of ^)
ex. [a-w&&[^c-g]z] ==> ([a-w] AND ([^c-g] OR z)) ==> [abh-w]
* If you want to use '[', '-', ']' as a normal character in a character class, you should escape these characters by '\'.
POSIX bracket ([:xxxxx:], negate [:^xxxxx:])
Not Unicode Case:
alnum alphabet or digit char
alpha alphabet
ascii code value: [0 - 127]
blank \t, \x20
cntrl
digit 0-9
graph include all of multibyte encoded characters
lower
print include all of multibyte encoded characters
punct
space \t, \n, \v, \f, \r, \x20
upper
word alphanumeric, "_" and multibyte characters
xdigit 0-9, a-f, A-F
Unicode Case:
alnum Letter | Mark | Decimal_Number
lpha Letter | Mark
ascii 0000 - 007F
blank Space_Separator | 0009
cntrl Control | Format | Unassigned | Private_Use | Surrogate
digit Decimal_Number
graph [[:^space:]] && ^Control && ^Unassigned && ^Surrogate
lower Lowercase_Letter
print [[:graph:]] | [[:space:]]
punct Connector_Punctuation | Dash_Punctuation | Close_Punctuation | Final_Punctuation | Initial_Punctuation | Other_Punctuation | Open_Punctuation
space Space_Separator | Line_Separator | Paragraph_Separator | 0009 | 000A | 000B | 000C | 000D | 0085
upper Uppercase_Letter
word Letter | Mark | Decimal_Number | Connector_Punctuation
xdigit 0030 - 0039 | 0041 - 0046 | 0061 - 0066 (0-9, a-f, A-F)
7. Extended groups
(?#...) comment
(?imx-imx) option on/off
i: ignore case
m: multi-line (dot(.) match newline)
x: extended form
(?imx-imx:subexp) option on/off for subexp
(?:subexp) not captured group
(subexp) captured group
(?=subexp) look-ahead
(?!subexp) negative look-ahead
(?<=subexp) look-behind
(?<!subexp) negative look-behind
Subexp of look-behind must be fixed character length. But different character length is allowed in top level alternatives only.
ex. (?<=a|bc) is OK. (?<=aaa(?:b|cd)) is not allowed.
In negative-look-behind, captured group isn't allowed, but shy group(?:) is allowed.
(?>subexp) atomic group
don't backtrack in subexp.
(?<name>subexp) define named group
(All characters of the name must be a word character. And first character must not be a digit or upper case)
Not only a name but a number is assigned like a captured group.
Assigning the same name as two or more subexps is allowed. In this case, a subexp call can not be performed although the back reference is possible.
8. Back reference
\n back reference by group number (n >= 1)
\k<name> back reference by group name
In the back reference by the multiplex definition name, a subexp with a large number is referred to preferentially. (When not matched, a group of the small number is referred to.)
* Back reference by group number is forbidden if named group is defined in the pattern and ONIG_OPTION_CAPTURE_GROUP is not set.
Back reference with nest level
\k<name+n> n: 0, 1, 2, ...
\k<name-n>n: 0, 1, 2, ...
Destinate relative nest level from back reference position.
ex 1.
/\A(?<a>|.|(?:(?<b>.)\g<a>\k<b+0>))\z/.match("reer")
ex 2.
r = Regexp.compile(<<'__REGEXP__'.strip, Regexp::EXTENDED)
(?<element> \g<stag> \g<content>* \g<etag> ){0}
(?<stag> < \g<name> \s* > ){0}
(?<name> [a-zA-Z_:]+ ){0}
(?<content> [^<&]+ (\g<element> | [^<&]+)* ){0}
(?<etag> </ \k<name+1> >){0}
\g<element>
__REGEXP__
p r.match('<foo>f<bar>bbb</bar>f</foo>').captures
9. Subexp call ("Tanaka Akira special")
\g<name> call by group name
\g<n> call by group number (n >= 1)
* left-most recursive call is not allowed.
ex. (?<name>a|\g<name>b) => error
(?<name>a|b\g<name>c) => OK
* Call by group number is forbidden if named group is defined in the pattern and ONIG_OPTION_CAPTURE_GROUP is not set.
* If the option status of called group is different from calling position then the group's option is effective.
ex. (?-i:\g<name>)(?i:(?<name>a)){0} match to "A"
10. Captured group
Behavior of the no-named group (...) changes with the following conditions. (But named group is not changed.)
case 1. /.../ (named group is not used, no option)
(...) is treated as a captured group.
(...) is treated as a no-captured group (?:...).
case 3. /..(?<name>..)../ (named group is used, no option)
(...) is treated as a no-captured group (?:...).
numbered-backref/call is not allowed.
case 4. /..(?<name>..)../G (named group is used, 'G' option)
(...) is treated as a captured group.
numbered-backref/call is allowed.
where
g: ONIG_OPTION_DONT_CAPTURE_GROUP
G: ONIG_OPTION_CAPTURE_GROUP
A-1. Syntax dependent options
+ RUBY
(?m): dot(.) match newline
+ PERL and JAVA
(?s): dot(.) match newline
(?m): ^ match after newline, $ match before newline
A-2. Original extensions
+ hexadecimal digit char type \h, \H
+ named group (?<name>...)
+ named backref \k<name>
+ subexp call \g<name>, \g<group-num>
A-3. Missing features compared with perl 5.8.0
+ \N{name}
+ \l,\u,\L,\U, \X, \C
+ (?{code})
+ (??{code})
+ (?(condition)yes-pat|no-pat)
* \Q...\E
This is effective on PERL and JAVA.
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