Using regular expressions

Source: Internet
Author: User
Tags expression regular expression string
Regular

In a typical search and replace operation, you must provide the exact text you want to find. This technique may be sufficient for simple search and replace tasks in static text, but because of its lack of flexibility, it is difficult or even impossible to search for dynamic text.

Using regular expressions, you can:

  • Tests a pattern of a string. For example, you can test an input string to see if there is a phone number pattern or a credit card number pattern in the string. This is known as data validation.
  • Replaces text. You can use a regular expression in your document to identify specific text, and then you can delete it all, or replace it with another text.
  • Extracts a substring from a string based on pattern matching. Can be used to find specific text in text or input fields.

For example, if you need to search the entire Web site to remove some outdated material and replace some HTML formatting tags, you can use regular expressions to test each file to see if there are any material or HTML formatting tags that you want to find in the file. With this method, you can narrow the affected file range to those files that contain the material you want to delete or change. You can then use regular expressions to delete obsolete materials, and finally, you can use regular expressions again to find and replace those that need to be replaced.

Another example that illustrates the usefulness of regular expressions is a language whose string-handling power is not yet known. VBScript is a subset of Visual Basic that has rich string processing capabilities. Jscript similar to C does not have this ability. Regular expressions make a noticeable improvement in the string handling capabilities of JScript. However, it may be more efficient to use regular expressions in VBScript, which allows multiple string operations to be performed in a single expression.



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