Research Oniguruma Regex

[ghost]

Please write documentation on what you find as a comment here.

[picchietti]

[DOCUMENTATION]

From here

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,

     + works on EUC_JP, Shift_JIS
       Hiragana, Katakana

     + works on UTF8, UTF16, UTF32
       Any, Assigned, C, Cc, Cf, Cn, Co, Cs, L, Ll, Lm, Lo, Lt, Lu,
       M, Mc, Me, Mn, N, Nd, Nl, No, P, Pc, Pd, Pe, Pf, Pi, Po, Ps,
       S, Sc, Sk, Sm, So, Z, Zl, Zp, Zs, 
       Arabic, Armenian, Bengali, Bopomofo, Braille, Buginese,
       Buhid, Canadian_Aboriginal, Cherokee, Common, Coptic,
       Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian,
       Glagolitic, Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul,
       Hanunoo, Hebrew, Hiragana, Inherited, Kannada, Katakana,
       Kharoshthi, Khmer, Lao, Latin, Limbu, Linear_B, Malayalam,
       Mongolian, Myanmar, New_Tai_Lue, Ogham, Old_Italic, Old_Persian,
       Oriya, Osmanya, Runic, Shavian, Sinhala, Syloti_Nagri, Syriac,
       Tagalog, Tagbanwa, Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan,
       Tifinagh, Ugaritic, Yi

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
      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    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
      xdigit   0030 - 0039 | 0041 - 0046 | 0061 - 0066
               (0-9, a-f, A-F)
      word     Letter | Mark | Decimal_Number | Connector_Punctuation

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), (?'name'subexp)
                     define named group
                     (All characters of the name must be a word character.)

                     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<n>       back reference by group number (n >= 1)
  \k'n'       back reference by group number (n >= 1)
  \k<-n>      back reference by relative group number (n >= 1)
  \k'-n'      back reference by relative group number (n >= 1)
  \k<name>    back reference by group name
  \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 setted.

  back reference with nest level

    level: 0, 1, 2, ...

    \k<n+level>     (n >= 1)
    \k<n-level>     (n >= 1)
    \k'n+level'     (n >= 1)
    \k'n-level'     (n >= 1)

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

    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