C# Cookbook

8.12. Using Common Patterns

Problem

You need a quick list from which to choose regular expression patterns that match standard items. These standard items could be a Social Security Number, a zip code, a word containing only characters, an alphanumeric word, an email address, a URL, dates, or one of many other possible items used throughout business applications.

These patterns can be useful in making sure that a user has input the correct data and that it is well-formed. These patterns can also be used as an extra security measure to keep hackers from attempting to break your code by entering strange or malformed input (e.g., SQL injection or cross-site-scripting attacks). Note that these regular expressions are not a silver bullet that will stop all attacks on your system; rather, they are an added layer of defense.

Solution

• Match only alphanumeric characters along with the characters -, +, ., and any whitespace:

  ^([\w\.+-]|\s)*$

  Tip

  Be careful using the - character within a character class—a regular expression enclosed within [ and ]. That character is also used to specify a range of characters, as in a--z for a through z inclusive. If you want to use a literal - character, either escape it with \ or put it at the end of the expression, as shown in the previous and next examples.

• Match only alphanumeric characters along with the characters -, +, ., and any whitespace, with the stipulation that there is at least one of these characters and no more than 10 of these characters: ...