In a typical search and replace operation, you must provide the exact text you are looking for. 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.
With regular expressions, you can:
For example, if you need to search an entire web site to remove some outdated material and replace some HTML formatting tags, you can use a regular expression to test each file to see if the material or the HTML formatting tags you are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 You can then use a regular expression to remove the outdated material, and finally, you can use regular expressions to search for and replace the tags that need replacing.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 isn't 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.