syntax: ONIG_SYNTAX_ONIGURUMA (default syntax)

Syntax elements

\ escape (enable or disable meta character) | alternation (...) group [...] character class
Characters

\t horizontal tab (0x09) \v vertical tab (0x0B)
newline (line feed) (0x0A) \r carriage return (0x0D) backspace (0x08) \f form feed (0x0C) bell (0x07) escape (0x1B) \nnn octal char (encoded byte value) \xHH hexadecimal char (encoded byte value) \x{7HHHHHHH} (1-8 digits) hexadecimal char (code point value) \o{17777777777} (1-11 digits) octal char (code point value) \uHHHH hexadecimal char (code point value) \cx control char (code point value) \C-x control char (code point value) \M-x meta (x|0x80) (code point value) \M-\C-x meta control char (code point value)

(* as backspace is effective in character class only)

2.1 Code point sequences

Hexadecimal code point (1-8 digits) \x{7HHHHHHH 7HHHHHHH ... 7HHHHHHH}

Octal code point (1-11 digits) \o{17777777777 17777777777 ... 17777777777}

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 case:
       U+0009, U+000A, U+000B, U+000C, U+000D, U+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-hexdigit char

\R general newline (* can't be used in character-class) "\r\n" or
,\v,\f,\r (* but doesn't backtrack from \r
to \r)

Unicode case: "\r\n" or
,\v,\f,\r or U+0085, U+2028, U+2029

\N negative newline (?-m:.)

\O true anychar (?m:.) (* original function)

\X Text Segment \X === (?>\O(?:\Y\O)*)

     The meaning of this operator changes depending on the setting of
     the option (?y{..}).

     \X doesn't check whether matching start position is boundary or not.
     Please write as \y\X if you want to ensure it.

     [Extended Grapheme Cluster mode] (default)
       Unicode case:
         See [Unicode Standard Annex #29: http://unicode.org/reports/tr29/]

       Not Unicode case:  \X === (?>\r\n|\O)

     [Word mode]
       Currently, this mode is supported in Unicode only.
       See [Unicode Standard Annex #29: http://unicode.org/reports/tr29/]

Character Property

{property-name}
{^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
works on EUC_JP, Shift_JIS Hiragana, Katakana
works on UTF8, UTF16, UTF32 See doc/UNICODE_PROPERTIES.

Quantifier

greedy

? 1 or 0 times
- 0 or more times
- 1 or more times {n,m} (n <= m) at least n but no more than m times {n,} at least n times {,n} at least 0 but no more than n times ({0,n}) {n} n times
reluctant

?? 0 or 1 times *? 0 or more times +? 1 or more times {n,m}? (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}? is reluctant operator in ONIG_SYNTAX_JAVA and ONIG_SYNTAX_PERL only. (In that case, it doesn't make sense to write so.) In default syntax, /a{n}?/ === /(?:a{n})?/

possessive (greedy and does not backtrack once match)

?+ 1 or 0 times *+ 0 or more times ++ 1 or more times {n,m} (n > m) at least m but not more than n times

{n,m}+, {n,}+, {n}+ are possessive operators in ONIG_SYNTAX_JAVA and ONIG_SYNTAX_PERL only.

ex. /a*+/ === /(?>a*)/

Anchors

^ beginning of the line $ end of the line word boundary \B non-word boundary

\A beginning of string \Z end of string, or before newline at the end \z end of string \G where the current search attempt begins \K keep (keep start position of the result string)

\y Text Segment boundary \Y Text Segment non-boundary

    The meaning of these operators(\y, \Y) changes depending on the setting
    of the option (?y{..}).

    [Extended Grapheme Cluster mode] (default)
      Unicode case:
        See [Unicode Standard Annex #29: http://unicode.org/reports/tr29/]

      Not Unicode:
        All positions except between \r and \n.

    [Word mode]
      Currently, this mode is supported in Unicode only.
      See [Unicode Standard Annex #29: http://unicode.org/reports/tr29/]

Character class

^... negative class (lowest precedence) x-y range from x to y [...] set (character class in character class) ..&&.. intersection (low precedence, only higher than ^)

ex. [a-w&&[^c-g]z] ==> ([a-w] AND ([^c-g] OR z)) ==> [abh-w]
- If you want to use '[', '-', or ']' as a normal character in character class, you should escape them with '\'.
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,
, \v, \f, \r, \x20 upper xdigit 0-9, a-f, A-F word alphanumeric, "_" and multibyte characters

Unicode Case:

  alnum    Letter | Mark | Decimal_Number
  alpha    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    Punctuation | Symbol
  space    Space_Separator | Line_Separator | Paragraph_Separator |
           U+0009 | U+000A | U+000B | U+000C | U+000D | U+0085
  upper    Uppercase_Letter
  xdigit   U+0030 - U+0039 | U+0041 - U+0046 | U+0061 - U+0066
           (0-9, a-f, A-F)
  word     Letter | Mark | Decimal_Number | Connector_Punctuation

Extended groups

(?#...) comment

(?imxWDSPy-imxWDSP:subexp) option on/off for subexp
```
                     i: ignore case
                     m: multi-line (dot (.) also matches newline)
                     x: extended form
                     W: ASCII only word (\w, \p{Word}, [[:word:]])
                        ASCII only word bound (\b)
                     D: ASCII only digit (\d, \p{Digit}, [[:digit:]])
                     S: ASCII only space (\s, \p{Space}, [[:space:]])
                     P: ASCII only POSIX properties (includes W,D,S)
                        (alnum, alpha, blank, cntrl, digit, graph,
                         lower, print, punct, space, upper, xdigit, word)

                     y{?}: Text Segment mode
                        This option changes the meaning of \X, \y, \Y.
                        Currently, this option is supported in Unicode only.

                        y{g}: Extended Grapheme Cluster mode (default)
                        y{w}: Word mode
                        See [Unicode Standard Annex #29]
```
(?imxWDSPy-imxWDSP) isolated option
```
                * It makes a group to the next ')' or end of the pattern.
                  /ab(?i)c|def|gh/ == /ab(?i:c|def|gh)/
```
- (?i) option has no effect on word types (\w, {Word}). However, if the word types are used within a character class, it is valid. But, this would only be a concern when word types are used with the (?W) option.
/(?CIL).../, /(?CIL:...)/ whole option
```
                      This option must be placed in a position that
                      affects the entire regular expression.

                      C: ONIG_OPTION_DONT_CAPTURE_GROUP
                      I: ONIG_OPTION_IGNORECASE_IS_ASCII
                      L: ONIG_OPTION_FIND_LONGEST
```
(?:subexp) non-capturing group (subexp) capturing group

(?=subexp) look-ahead (?!subexp) negative look-ahead

(?<=subexp) look-behind (?<!subexp) negative look-behind
```
               * Cannot use Absent stopper (?~|expr) and Range clear
                 (?~|) operators in look-behind and negative look-behind.

               * In look-behind and negative look-behind, support for
                 ignore-case option is limited. Only supports conversion
                 between single characters. (Does not support conversion
                 of multiple characters in Unicode)
```
(?>subexp) atomic group no backtracks in subexp.

(?<name>subexp), (?'name'subexp) define named group (Each character of the name must be a word character.)

Not only a name but a number is assigned like a capturing group.

Assigning the same name to two or more subexps is allowed.

<Callouts>
- Callouts of contents (?{...contents...}) callout in progress (?{...contents...}D) D is a direction flag char D = 'X': in progress and retraction '<': in retraction only '>': in progress only (?{...contents...}[tag]) tag assigned (?{...contents...}[tag]D)
```
                        * Escape characters have no effects in contents.
                        * contents is not allowed to start with '{'.
```
  (?{{{...contents...}}}) n times continuations '}' in contents is allowed in (n+1) times continuations {{{...}}}.
  
  Allowed tag string characters: _ A-Z a-z 0-9 (* first character: _ A-Z a-z)
- Callouts of name (*name) (*name{args...}) with args (*name[tag]) tag assigned (*name[tag]{args...})
  
  Allowed name string characters: _ A-Z a-z 0-9 (* first character: _ A-Z a-z) Allowed tag string characters: _ A-Z a-z 0-9 (* first character: _ A-Z a-z)
<Absent functions>

(?~absent) Absent repeater (* proposed by Tanaka Akira) This works like .* (more precisely \O*), but it is limited by the range that does not include the string match with <absent>. This is a written abbreviation of (?~|(?:absent)|\O*). \O* is used as a repeater.

(?~|absent|exp) Absent expression (* original) This works like "exp", but it is limited by the range that does not include the string match with <absent>.

ex. (?~|345|\d*) "12345678" ==> "12", "1", ""

(?~|absent) Absent stopper (* original) After passed this operator, string right range is limited at the point that does not include the string match with <absent>.

(?~|) Range clear Clear the effects caused by Absent stoppers.
- Nested Absent functions are not supported and the behavior is undefined.
<if-then-else>

(?(condition_exp)then_exp|else_exp) if-then-else (?(condition_exp)then_exp) if-then
```
         condition_exp can be a backreference number/name or a normal
         regular expression.
         When condition_exp is a backreference number/name, both then_exp and
         else_exp can be omitted.
         Then it works as a backreference validity checker.
```
[ Backreference validity checker ] (* original)

(?(n)), (?(-n)), (?(+n)), (?(n+level)) ... (?(<n>)), (?('-n')), (?(<+n>)) ... (?(<name>)), (?('name')), (?(<name+level>)) ...
Backreferences

When we say "backreference a group," it actually means, "re-match the same text matched by the subexp in that group."

\k<n> \k'n' (n >= 1) backreference the nth group in the regexp \k<-n> \k'-n' (n >= 1) backreference the nth group counting backwards from the referring position \k<+n> \k'+n' (n >= 1) backreference the nth group counting forwards from the referring position \k<name> \k'name' backreference a group with the specified name

When backreferencing with a name that is assigned to more than one groups, the last group with the name is checked first, if not matched then the previous one with the name, and so on, until there is a match.
- Backreference by number is forbidden if any named group is defined and ONIG_OPTION_CAPTURE_GROUP is not set.
backreference with recursion level

(n >= 1, level >= 0)

\k<n+level> \k'n+level' \k<n-level> \k'n-level'

\k<name+level> \k'name+level' \k<name-level> \k'name-level'

Destine a group on the recursion level relative to the referring position.

ex 1.

/\A(?|.|(?:(?.)\g\k))\z/.match("reee") /\A(?|.|(?:(?.)\g\k<b+0>))\z/.match("reer")

\k<b+0> refers to the (?.) on the same recursion level with it.

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
Subexp calls ("Tanaka Akira special") (* original function)

When we say "call a group," it actually means, "re-execute the subexp in that group."

\g<n> \g'n' (n >= 1) call the nth group \g<0> \g'0' call zero (call the total regexp) \g<-n> \g'-n' (n >= 1) call the nth group counting backwards from the calling position \g<+n> \g'+n' (n >= 1) call the nth group counting forwards from the calling position \g<name> \g'name' call the group with the specified name
Captured group

Behavior of an unnamed 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 capturing group.

case 2. /.../g (named group is not used, 'g' option)

(...) is treated as a non-capturing group (?:...).

case 3. /..(?<name>..)../ (named group is used, no option)

(...) is treated as a non-capturing group. numbered-backref/call is not allowed.

case 4. /..(?<name>..)../G (named group is used, 'G' option)

(...) is treated as a capturing group. numbered-backref/call is allowed.

where g: ONIG_OPTION_DONT_CAPTURE_GROUP G: ONIG_OPTION_CAPTURE_GROUP

('g' and 'G' options are argued in ruby-dev ML)

A-1. Syntax-dependent options

ONIG_SYNTAX_ONIGURUMA (?m): dot (.) also matches newline

ONIG_SYNTAX_PERL and ONIG_SYNTAX_JAVA (?s): dot (.) also matches newline (?m): ^ matches after newline, $ matches before newline

A-2. Original extensions

hexadecimal digit char type \h, \H

true anychar \O

text segment boundary \y, \Y

backreference validity checker (?(...))

named group (?<name>...), (?'name'...)

named backref \k<name>

subexp call \g<name>, \g<group-num>

absent expression (?~|...|...)

absent stopper (?~|...)

A-3. Missing features compared with perl 5.8.0

\N{name}

\l,\u,\L,\U,\C

(??{code})

\Q...\E This is effective on ONIG_SYNTAX_PERL and ONIG_SYNTAX_JAVA.

A-4. Differences with Japanized GNU regex(version 0.12) of Ruby 1.8

add character property ({property}, \P{property})

add hexadecimal digit char type (\h, \H)

add look-behind (?<=fixed-width-pattern), (?<!fixed-width-pattern)

add possessive quantifier. ?+, *+, ++

add operations in character class. [], && ('[' must be escaped as an usual char in character class.)

add named group and subexp call.

octal or hexadecimal number sequence can be treated as a multibyte code char in character class if multibyte encoding is specified. (ex. [\xa1\xa2], [\xa1\xa7-\xa4\xa1])

allow the range of single byte char and multibyte char in character class. ex. /[a-<<any EUC-JP character>>]/ in EUC-JP encoding.

effect range of isolated option is to next ')'. ex. (?:(?i)a|b) is interpreted as (?:(?i:a|b)), not (?:(?i:a)|b).

isolated option is not transparent to previous pattern. ex. a(?i)* is a syntax error pattern.

allowed unpaired left brace as a normal character. ex. /{/, /({)/, /a{2,3/ etc...

negative POSIX bracket [:^xxxx:] is supported.

POSIX bracket [:ascii:] is added.

repeat of look-ahead is not allowed. ex. /(?=a)*/, /(?!b){5}/

Ignore case option is effective to escape sequence. ex. /\x61/i =~ "A"

In the range quantifier, the number of the minimum is optional. /a{,n}/ == /a{0,n}/ The omission of both minimum and maximum values is not allowed. /a{,}/

/{n}?/ is not a reluctant quantifier. /a{n}?/ == /(?:a{n})?/

invalid back reference is checked and raises error. /\1/, /(a)\2/

Zero-width match in an infinite loop stops the repeat, then changes of the capture group status are checked as stop condition. /(?:()|())*\1\2/ =~ "" /(?:\1a|())*/ =~ "a"

// END