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Uses for Regular Expressions

A typical search and replace operation requires you to provide the exact text that matches the intended search result. Although this technique may be adequate for simple search and replace tasks in static text, it lacks flexibility and makes searching dynamic text at least difficult if not impossible.

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For example, you may need to search an entire Web site, remove outdated material, and replace some HTML formatting tags. In this case, you can use a regular expression to determine if the material or the HTML formatting tags appears in each file. This process reduces the affected files list to those that contain material targeted for removal or change. You can then use a regular expression to remove the outdated material. Finally, you can use a regular expression to search for and replace the tags.

A regular expression is also useful in a language, such as JScript or C that is not known for its string-handling ability.