Regex Notes

Capturing Groups and Back Reference (\d)\d\1    -> matches : 808,717,505  not matches : 456 ,446 ( ) capturing group \1 referance to first group captured. (?<d1>)(?<d2>)   referrance $+{d2} $+{d1}   naming a group (?:) non  capture the name or referance in memory ------------------- ?  : one or mone      -?   - is optional + : one or more      dd * :  zero or more , not one \d{2} : length 2    22,33,43,54 not: 3213,434,214 example \D  or  [^0-9]  or  [^\d]    :  non-digit \w  only word equal to [a-zA-Z0-9]    \W upper "w" is non-word .* : any matches ?i :  (keyword?i)  not case-sensitive  equal to (keyword|Keyword|KEYWORD|KEYword.....) HTML  matching tags transforming plain text with sed appending tags transforming plain text with perl Quantifier : 7{1,}  equals to 7+ one or more 7{0,}  equals to 7* zero or more 7{0,1}  equals to 7?  optioanl Regex website list 

1. http://regexpal.com/
2. http://www.regexr.com/