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Converting Wildcards to Regexes

, 15 Sep 2005
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Ever wondered how to do wildcards in C#?

Introduction

Ever wondered how to do wildcards in .NET? It's not hard, all you have to do is use regular expressions. But it's not always easy to figure it out either. I found that I had to dig around for a while to figure out how to do it properly.

Even though regexes are a lot more powerful, wildcards are still good in situations where you can't expect the user to know or learn the cryptic syntax of regexes. The most obvious example is in the file search functionality of practically all OSs -- there aren't many that don't accept wildcards. I personally need wildcards to handle the HttpHandlers tag in web.config files.

Note: This method is good enough for most uses, but if you need every ounce of performance with wildcards, here is a good place to start.

Using the Code

There are three steps to converting a wildcard to a regex:

  1. Escape the pattern to make it regex-safe. Wildcards use only * and ?, so the rest of the text has to be converted to literals.
  2. Once escaped, * becomes \* and ? becomes \?, so we have to convert \* and \? to their respective regex equivalents, .* and ..
  3. Prepend ^ and append $ to specify the beginning and end of the pattern.

So, here's the golden function:

public static string WildcardToRegex(string pattern)
{
  return "^" + Regex.Escape(pattern).
  Replace("\\*", ".*").
  Replace("\\?", ".") + "$";
}

Just to make it look cool, I wrapped it in a Wildcard class that inherits Regex.

/// <summary>
/// Represents a wildcard running on the
/// <see cref="System.Text.RegularExpressions"/> engine.
/// </summary>
public class Wildcard : Regex
{
 /// <summary>
 /// Initializes a wildcard with the given search pattern.
 /// </summary>
 /// <param name="pattern">The wildcard pattern to match.</param>
 public Wildcard(string pattern)
  : base(WildcardToRegex(pattern))
 {
 }
 
 /// <summary>
 /// Initializes a wildcard with the given search pattern and options.
 /// </summary>
 /// <param name="pattern">The wildcard pattern to match.</param>
 /// <param name="options">A combination of one or more
 /// <see cref="System.Text.RegexOptions"/>.</param>
 public Wildcard(string pattern, RegexOptions options)
  : base(WildcardToRegex(pattern), options)
 {
 }
 
 /// <summary>
 /// Converts a wildcard to a regex.
 /// </summary>
 /// <param name="pattern">The wildcard pattern to convert.</param>
 /// <returns>A regex equivalent of the given wildcard.</returns>
 public static string WildcardToRegex(string pattern)
 {
  return "^" + Regex.Escape(pattern).
   Replace("\\*", ".*").
   Replace("\\?", ".") + "$";
 }
}

You can use it like any other Regex -- case-(in)sensitivity, string replacement, matching and all.

// Get a list of files in the My Documents folder
string[] files = System.IO.Directory.GetFiles(
 System.Environment.GetFolderPath(
 Environment.SpecialFolder.Personal));

// Create a new wildcard to search for all
// .txt files, regardless of case
Wildcard wildcard = new Wildcard("*.txt", RegexOptions.IgnoreCase);

// Print all matching files
foreach(string file in files)
 if(wildcard.IsMatch(file))
  Console.WriteLine(file);

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

Rei Miyasaka

Canada Canada
The cows are here to take me home now...

Comments and Discussions

 
QuestionLicense information PinmemberMember 103749191-Nov-13 7:43 
QuestionThanks - just in time Pinmembersnoopy00116-May-13 5:31 
GeneralMy vote of 5 PinmemberChristopher Drake2-Jan-13 10:05 
GeneralMy vote of 5 PinmemberMember 892678824-Sep-12 0:33 
QuestionDoes not work with *.* Pinmemberguest2323113-Sep-12 4:23 
GeneralMy vote of 5 PinmemberKuthuparakkal12-Sep-12 18:03 
QuestionWord wild card matching behavior a little different from this [modified] Pinmemberweciii2-Mar-12 6:21 
GeneralMy vote of 5 Pinmembervet0n23-Feb-12 22:46 
SuggestionAdding More Static Methods PinmemberSina Iravanian14-Dec-11 3:21 
QuestionRe: Adding More Static Methods PinmemberDontSailBackwards6-May-13 15:47 
AnswerRe: Adding More Static Methods Pinmemberdrzaus1319-Sep-13 5:41 
GeneralMy vote of 5 PinmemberNagy Vilmos8-Nov-10 3:24 
The method WildcardToRegex has just saved me from having to write a very messy search class. TVM.
Generalbug?? with '.' Pinmemberalchemy916-Nov-09 5:07 
GeneralRe: bug?? with '.' PinmemberSteve Kutnar2-Sep-10 7:28 
QuestionHow to add other chars - [A-Z] [modified] Pinmemberboopathi_tpgit20-Oct-09 3:22 
GeneralDifference between httphandlers and httpmodules Pinmembergaurav200720-Jun-08 1:20 
GeneralRe: Difference between httphandlers and httpmodules Pinmemberreinux20-Jun-08 7:24 
NewsThere's a new version of the RegEx Tester Tool ! PinmemberBucanerO_Slacker2-Mar-08 0:18 
GeneralSmall suggestion PinmemberDavide Icardi16-Dec-07 23:12 
GeneralRe: Small suggestion Pinmemberphilippe dykmans31-May-08 16:39 
GeneralCorrection... Pinmemberphilippe dykmans31-May-08 16:45 
GeneralRe: Correction... PinmemberDavide Icardi1-Jun-08 14:19 
GeneralRe: Small suggestion Pinmembersssw285-Mar-11 22:25 
GeneralSimple, yet good Pinmembernorm .net16-May-07 23:33 
GeneralRe: Simple, yet good Pinmemberreinux17-May-07 6:32 

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