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 General_Category -- (Letter|Mark|Number|Connector_Punctuation) \W non word char \s whitespace char 0009, 000A, 000B, 000C, 000D, 0085(NEL), General_Category -- Line_Separator -- Paragraph_Separator -- Space_Separator \S non whitespace char \d decimal digit char General_Category -- Decimal_Number \D non decimal digit char \h hexadecimal digit char [0-9a-fA-F] \H non hexadecimal digit char 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 Note: {n,m}+, {n,}+, {n}+ are reluctant op. 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 (*) Ruby Regexp: previous end-of-match position (This specification is not related to this library.) 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:]) 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) 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 uppper 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.
Anyway, please note that we will accepts any bug reports, including the bug of libonig, and please do not report the bugs of our library to them.