Sunday, March 6, 2011

Regular Expression

Search for REGEXP

Boolean "or"
vertical bar separates alternatives. For example, gray|grey can match "gray" or "grey".
Parentheses are used to define the scope and precedence of the operators (among other uses). For example,gray|grey and gr(a|e)y are equivalent patterns which both describe the set of "gray" and "grey".
A quantifier after a token (such as a character) or group specifies how often that preceding element is allowed to occur. The most common quantifiers are the question mark ?, the asterisk * (derived from the Kleene star), and the plus sign + (Kleene cross).
?The question mark indicates there is zero or one of the preceding element. For example, colou?r matches both "color" and "colour".
*The asterisk indicates there are zero or more of the preceding element. For example, ab*c matches "ac", "abc", "abbc", "abbbc", and so on.
+The plus sign indicates that there is one or more of the preceding element. For example, ab+c matches "abc", "abbc", "abbbc", and so on, but not "ac".


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