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   Simple Regular Expression Reference Card

Any character except [\^$.|?*+() All characters except the special characters on the left match a single instance of themselves. { and } are literal characters, unless they're part of a valid regular expression token (e.g. the {n} quantifier). a
matches a
\ (backslash) followed by any of [\^$.|?*+(){} Escapes character to suppress the immediate following special character′ meaning. \+
matches +
\Q...\E Matches the characters between \Q and \E literally, suppressing the meaning of special characters. \Q+-*/\E
matches +-*/
\xHH where HH are 2 hexadecimal digits Matches HEX ASCII code of a character. \x21
matches !
\n, \r and \t Match LineFeed, Carrige Return and tab character respectively. \r\n matches a DOS CRLF.
\a, \e, \f and \v Match printer/keyboard special characters: bell character (\x07), escape character (\x1B), form feed (\x0C) and vertical tab (\x0B) respectively. Can be found in ASCII code page.  
\cA through \cZ Match keyboard code Control+A through Control+Z, equivalent to ASCII code\x01 through \x1A. \cS\cQ matches a stop and go on keyboard.
Character Sets [abc]
(opening square bracket)
Starts a character set. A character set contains all character within the range.  
Any character except ^-]\ can belongs to the character set. All characters except the special characters on the left. [abc]
matches a, b or c
A escapes special characters to suppress the special meaning ofi ^-]\. [\^\]]
matches ^ or ]
Specifies a range of characters if placed between characters and numbers. (represent a hyphen in the set, if placed immediately after [.) [a-z0-9]
matches any lower case letter or digit
Negates the character set if placed immediately after [, if placed anywhere except after the opening [, represent the caret belongs to the set [^A-C]
matches any character except A, B, or C)
The most important shorthand character, matches any single character except line break characters \r and \n. .
Matches any ONE character
^ Matches at the beginning of the string.  
$ Matches the end of the string.  
\A Start the regular expression match from the beginning of the string.  
\Z Position the regular expression match to the end of the string.  
Word Boundaries
\b This is a zero-width assertion that matches only at the beginning or end of a word. \bgreat\b
matches only "great" is a compelete word exist
\B Another zero-width assertion that is opposite the above. \Bhello\B success if there is no "hello" exist
\w Matches any alphanumeric character or string, including "_".  
\W Matches any non-alphanumeric character or string.  
| Match possible correct answers. a (2|two)-year-old girl
matches ether 2 or two, both are correct
? Lazy quantifier. Matches the preceding pattern element zero or one times. xyz? matches xy or xyz
* Matches the preceding pattern element zero or more times. Can not be placed at the first position as match pattern, since it can not repeat nothing. ".*"
default WebMux match pattern to match anything in anylength
+ Matches the preceding pattern element one or more times. "l+"
If the URL contains "hello", it will be matched.
None Greedy Match
Modify the "+" regular expression to match as few time as possible.  
An integer in curly brackets
Repeats the preceeding character n times. t{3} return true if ttt exist
{M,N} Denotes the minimum M and the maximum N match count. M,N must be > 0. l{1,2} matches Hello, World but not here

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