ASP Kitchen: Classic ASP Articles: VBScript Regular Expressions: Subexpression Substitutions

VBScript Regular Expressions: Subexpression Substitutions

Introduction

Although there are a good range of text handling functions in VBScript, there are times when the required text replacement operation would be very tricky to carry out with a combination of calls to functions such as Replace, InStr and Left. In these cases, it is worth considering the use of VBScript's regular expressions, which are supported from VBScript version 5 upwards. An introduction to VBScript Regular Expressions is available.

Complex Substitutions

A typical use of regular expression substitutions is to process the BBCode tags into HTML. BBCode is a simplified version of HTML used by web-based applications such as the phpBB bulletin board. For example, if the user wishes to insert a hyperlink in their message then they can either use the BBCode:

[url]http://www.aspalliance.com/[/url]   .... which the bulletin board changes to: http://www.aspalliance.com/.

Alternatively, if anchor text is required then this BBCode is used:

[url=http://www.aspalliance.com/]AspAlliance.Com[/url]   .... which the bulletin board changes to: AspAlliance.Com.

Changing [url]http://www.aspalliance.com/[/url] to a Hyperlink

To change the first BBCode snippet to HTML, the following code can be used:

<%
InitialString = "[url]http://www.aspalliance.com[/url]"

Set RegularExpressionObject = New RegExp

With RegularExpressionObject
.Pattern = "\[url\]([^\]]+)\[\/url\]"
.IgnoreCase = True
.Global = True
End With

ReplacedString = RegularExpressionObject.Replace(InitialString, "<a href=""$1"">$1</a>")

Response.Write "Replaced " & InitialString & " with: " & ReplacedString
%>

The text replacement is achieved using the Replace method of a RegExp object. The method takes two arguments:

• The first argument is the string to be searched.
• The second argument is the replacement to be made.

The regular expression specified by setting the Pattern property of the RegExp object is \[url\]([^\]]+)\[\/url\], which matches the following pattern:

• \[ = Matches an opening square bracket.
• url = Matches the text url.
• \] = Matches a closing square bracket.
• ([^\]]+) = Match one or more of any character except for the character enclosed in square brackets, which in this instance is a closing square bracket. This part of the pattern (which matches the URL between the BBCode [url] ... [/url] tags) is enclosed in parenthesis because it needs to be remembered for the substitution.
• \[\/url\] = Matches the closing BBCode url tag.

Note that because square brackets ([ ]) and forward slashes (/) have special meanings in regular expressions, they have to be "escaped" by prefixing them with a backward slash (\).

In this example, the URL specified between the BBCode [url] ... [/url] tags is "remembered" because it is within a set of parenthesis. As a result, it can be used in the replacement by using a dollar sign immediately followed by the number of the subpattern in the regular expression. There can be more than one set of parenthesis in a regular expression pattern. This makes it possible to reorder text in substitutions - see the next section for more details of this.

Changing [url]http://www.aspalliance.com/[/url] to a Hyperlink

To change [url=http://www.aspalliance.com/]AspAlliance.Com[/url] to a hyperlink with http://www.aspalliance.com/ as the URL and AspAlliance.Com as the anchor text (i.e. the HTML equivalent of <a href="http://www.aspalliance.com/">AspAlliance.Com</a>) a more complex regular expression subsitution may be used:

<%
InitialString = "[url=http://www.aspalliance.com/]AspAlliance.Com[/url]"

Set RegularExpressionObject = New RegExp

With RegularExpressionObject
.Pattern = "\[url=([^\]]+)\]([^\]]+)\[\/url\]"
.IgnoreCase = True
.Global = True
End With

ReplacedString = RegularExpressionObject.Replace(InitialString, "<a href=""$1"">$2</a>")


Response.Write "Replaced " & InitialString & " with: " & ReplacedString

Set RegularExpressionObject = nothing
%>

In this example, there are two sets of parenthesis which match the subpattern of the URL (i.e. http://www.aspalliance.com) and the anchor text (i.e. AspAlliance.Com). These are accessible in the RegExp object's Replace method as $1 and $2, respectively.

As mentioned previously, these patterns may be used in a different order to the way they were matched. They can also be used more than once. For example, this line adds additional HTML to include a title attribute for the a tag:

ReplacedString = RegularExpressionObject.Replace(InitialString, "<a href=""$1"" title=""Visit $2 ($1)"">$2</a>")

This replacement produces the HTML:

<a href="http://www.aspalliance.com/" title="Visit AspAlliance.Com (http://www.aspalliance.com/)">AspAlliance.Com</a>

Useful Development Tools

ASP Documentation Tool™

Automatically creates technical documentation for ASP 2.0 and 3.0 web applications written in VBScript and JScript. Documentation for Microsoft Access, SQL Server 7/2000 databases and Visual Basic 6.0 components associated with the web application can also be incorporated into the reports. Documentation is created in HTML, HTML Help and plain text formats.

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.NET Documentation Tool

Automatically creates technical documentation for .NET Framework applications written in C# or VB.NET (including ASP.NET). Documentation for SQL Server 7/2000/2005 databases and C#/VB.NET components associated with the web application can also be incorporated into the reports. Documentation is created in HTML, HTML Help and plain text formats. Additional support for ASP.NET web applications. A useful alternative to NDoc!

View Sample Output (HTML Help format).     View Sample Output (HTML Format).     Download Trial Version (3Mb ZIP file).

SQL Documentation Tool

The SQL Documentation Tool creates technical documentation for Microsoft SQL Server 7.0, 2000 and 2005 databases. Technical documentation is created in HTML and HTML Help formats. The HTML Help format documentation is fully searchable and cross referenced. The SQL Documentation Tool documents SQL Server Tables, Views, Stored Procedures, Triggers, Table Relationships, Jobs and DTS Packages.

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VB Documentation Tool

The VB Documentation Tool creates technical documentation for Microsoft Visual Basic 6.0 projects. Technical documentation is created in HTML and HTML Help formats. The HTML Help format documentation is fully searchable and cross referenced.

View Sample Output (HTML Help format).     View Sample Output (HTML Format).     Download Trial Version (1Mb ZIP file).

The Website Utility

The Website Utility examines websites for errors and areas that need to be optimised for search engines by using a built in web crawling engine. Errors checked for include broken or moved hyperlinks, missing page titles and missing meta tags. It also generates HTML for use in creating website site maps (table of contents pages - like this one), and is able to create both client-side JavaScript search engines and server-side ASP search engines and ASP.NET search engines for a website.

View Sample Output (HTML Format).     Download Trial Version (3Mb ZIP file).

Text Workbench

Text Workbench is a file search and replacement utility for text files and Microsoft Office documents. Make rapid file replacements on multiple files and folders full of files. Advanced replacement options include regular expressions support. It even works on remote file systems via FTP. A Regular Expression Laboratory allows advanced pattern matching and replacement expressions to be built and tested. This great utility will make your everyday development tasks much easier!

Download Trial Version (3Mb ZIP file; you have the option to either install directly from this link or save the file for later installation).

Indexing Service Companion

The Indexing Service Companion is a utility that extends the functionality of the Microsoft Windows Indexing Service so that it is able to index content from any remote website and also from ODBC compliant databases. As such it can be used as a low cost alternative to Sharepoint's Search Services.

View Product Documentation (119K ZIP file).     Try Sample Search Facility.     Download Trial Version (1.7Mb ZIP file).

ASP Spell Check

ASPSpellCheck is the easy way to add spell checking capabilities to your ASP or ASP.NET websites, Intranets and web applications. The utility allows you to add spell checking capabilities to any HTML text field or rich content editing text box. It works with all common web browsers, and there are no components or databases to install on the server.

Read ASPSpellCheck Review.     View ASPSpellCheck Examples.     Download Trial Version (3Mb ZIP file; you have the option to either install directly from this link or save the file for later installation).

Author details

Brett Burridge has worked as a web developer since 1997 and has developed web applications for a range of corporations, start up busiensses and educational establishments.

Brett is presently employed as an Internet developer and technical writer through his own company, Winnersh Triangle Web Solutions Limited. The company produces a number of innovative products, including a range of software documentation tools, which include the ASP Documentation Tool™, the .NET Documentation Tool for VB.NET and C#, and the SQL Server Documentation Tool. Other products include The Website Utility, which functions as a website error checker, search engine optimizer and ASP/ASP.NET search engine builder application.

As well as the ASPAlliance, Brett has written articles for Ariadne.ac.uk, ASPToday, the software documentation portal www.softwaredocumentation.info, and has contributed recipes to the ASP.NET Developer's Cookbook.    links

Outside web development, Brett is interested in travelling (here are my travel logs from New York, Hong Kong and Tokyo), digital photography (here's my photo gallery), tropical fishkeeping and collecting contemporary works of art by artists such as Doug Hyde.

Contact Brett by emailing

Article history

"VBScript Regular Expressions: Subexpression Substitutions" published on ASPAlliance.com on 28 October 2004.

ASP Kitchen: Classic ASP Articles: VBScript Regular Expressions: Subexpression Substitutions