In a typical search and replace operation, you must provide the exact text for which you are searching. That technique may be adequate for simple search and replace tasks in static text, but it lacks flexibility and makes searching dynamic text difficult, if not impossible.
Flexibility of Regular Expressions
With regular expressions, you can:
Test for a pattern within a string. For example, you can test an input string to see if a telephone number pattern or a credit card number pattern occurs within the string. This is called data validation.
Replace text. You can use a regular expression to identify specific text in a document and either remove it completely or replace it with other text.
Extract a substring from a string based upon a pattern match. You can find specific text within a document or input field
For example, if you need to search an entire web site to remove some outdated material and replace some HTML formatting tags, you can use a regular expression to test each file to see if the material or the HTML formatting tags you are looking for exists in that file. That way, you can narrow down the affected files to only those that contain the material that has to be removed or changed. You can then use a regular expression to remove the outdated material, and finally, you can use regular expressions to search for and replace the tags that need replacing.
Another example of where a regular expression is useful occurs in a language that is not known for its string-handling ability. VBScript, a subset of Visual Basic, has a rich set of string-handling functions. JScript, like C, does not. Regular expressions provide a significant improvement in string-handling for JScript. However, regular expressions may also be more efficient to use in VBScript as well, allowing you do perform multiple string manipulations in a single expression.