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Common Applications of Regular Expressions, Part 4

By Richard Lowe


  • Read Part 1
  • Read Part 2
  • Read Part 3

  • In Part 3 we looked at parsing data files with regular expressions. In this final part, we'll look at how to use regular expressions to perform powerful string replacements!

    Replacing Values
    The final example we'll look at is the replace functionality of regular expressions in VBScript. ASP often is called to dynamically apply formatting to the text it retrieves from the numerous data sources it has available to it. One handy feature of VBScript's regular expressions allow it to modify the complex patterns it matches. A prime example of this is the highlighting of certain words, such as keywords in a search by adding HTML tags.

    To illustrate this, here is an example of highlighting all references to ".NET" in a string. This string could easily come from any source, such as a database or another web site.

    <%
      Set regEx = New RegExp
      regEx.Global = true
      regEx.IgnoreCase = True
    
      ' Pattern finds any word (or URL) with
      ' .NET on the end of it
      regEx.Pattern = "(\b[a-zA-Z\._]+?\.NET\b)"
    
      ' Input a string to test our replace functionality:  
      strText = ""
      strText = strText & "Microsoft has launched a new Web site," & _
                          " www.ASP.NET. " & vbCrLf & "This Web site (as you " & _
                          "can probably guess) contains information " & vbCrLf
      strText = strText & "on the next ""version"" of ASP: ASP.NET. The site " & _
                          "contains links to " & vbCrLf & "download the latest " & _
                          "ASP.NET bits, contains a FAQ section, links " & vbCrLf
      strText = strText & "to ASP community sites, and other great information. " & _
                          "To learn more " & vbCrLf & "about ASP.NET, check out " & _
                          "www.ASP.NET and the 4Guys ASP.NET " & vbCrLf
      strText = strText & "Article Index! " & vbCrLf
    
      ' Call Replace method of the regular expression: 
      ' the $1 means place the matching text here
      Response.Write regEx.Replace(strText, _
                     "<b style='color: #000099; font-size: 18pt'>$1</b>")
    %>
    
    [View the live demo!]

    In this example, there are several important things to note. The whole regular expression is enclosed in parenthesis - (). This tells it to capture any pattern it matches for use later. This captured match is then referenced in the replacement text by $1. Up to nine such captures can be done per match, referenced by $1 to $9. The Replace method of the regular expression object is different from the Replace global function in VBScript. It takes only two parameters, the string to search in and the replacement text.

    Also in the example, a bold tag, with other style attributes was added to surround matching text for emphasis on the ".NET" matches. A search and replace like this could easily highlight search terms from a search of your site, or place automatic links to other pages on keywords that appear in any text.

    Conclusion
    I hope this exploration of some of the uses of regular expressions have given you ideas about how and where to use them in your web applications. Regular expressions are a very powerful way to extend the functionality of VBScript and JScript's string handling. Visual Basic applications, as well, can benefit from regular expressions. Microsoft has made the VBScript and JScript RegExp objects available to VB (or any COM-aware language). Just select Microsoft VBScript Regular Expressions under Project --> References and the RegExp object is available to extend your VB application's string handling, as well.

    There is also a bright future for regular expressions in ASP.NET, as they provide the mechanism for one of the major forms of server control form validation, and are exposed throughout the whole .NET framework in the System.Text.RegularExpressions namespace! (To learn more about ASP.NET, be sure to check out the ASP.NET Article Index Happy Programming!

    Richard Lowe works as a Development Services Consultant for Spherion's Technology Business Solutions Group...


    Article Information
    Article Title: Common Applications of Regular Expressions
    Article Author: Richard Lowe
    Published Date: Monday, December 04, 2000
    Article URL: http://www.4GuysFromRolla.com/webtech/120400-1.4.shtml


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