Regular Expression

Regular expression is a technology of using an expression to compare with the text being searched. The expression used for comparing is a pattern of characters which are constructed following some rules and regulation. By matching the expression with the text string, regular expression can be used to search for patterns in the text, to replace strings of the text and to extract substrings of the text.

Regular Expression Engine

 

Regular Expression Features

The features of patterns used in regular expression can be grouped into serveral categories.

Special Characters

To a regular expression engine, special characters are metacharacters that represents a special meaning instead of the literal letter itself. Double quotes " and slash / are used as the delimiters of a literal regular exression pattern in VBScript and JScript accordingly. Backslash \ is a universal praser of a token. Asterisk *, plus +, question mark ?, dollar $, period ., opening bracket [, closing bracket ], opening brace {, closing brace }, open parenthesis (, close parenthesis ), vertical bar |,  are special control characters of a regular expression pattern. Hyphen - is a special control character of a character set. While caret ^ is a special control character for both a regular expression pattern and a regular character set with two different meanings accordingly.