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Converting Wildcards to Regexes

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15 Sep 20051 min read 312.4K   67   45
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:

C#
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.

C#
/// <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.

C#
// 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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Comments and Discussions

 
GeneralRe: Correction... Pin
Davide Icardi1-Jun-08 13:19
Davide Icardi1-Jun-08 13:19 
GeneralRe: Small suggestion Pin
sssw285-Mar-11 21:25
sssw285-Mar-11 21:25 
GeneralSimple, yet good Pin
NormDroid16-May-07 22:33
professionalNormDroid16-May-07 22:33 
Good solution.

.net is a box of never ending treasures, every day I get find another gem.

GeneralRe: Simple, yet good Pin
Rei Miyasaka17-May-07 5:32
Rei Miyasaka17-May-07 5:32 
GeneralJust what I was looking for. Pin
Ryan McFarren12-Apr-07 7:55
Ryan McFarren12-Apr-07 7:55 
GeneralRe: Just what I was looking for. Pin
Rei Miyasaka12-Apr-07 13:24
Rei Miyasaka12-Apr-07 13:24 
GeneralNICE Pin
Ben Allfree10-Mar-07 5:10
Ben Allfree10-Mar-07 5:10 
GeneralRe: NICE Pin
Rei Miyasaka10-Mar-07 12:24
Rei Miyasaka10-Mar-07 12:24 
QuestionDoesnt work with input string containing meta characters Pin
skk-ws31-Jan-06 6:41
skk-ws31-Jan-06 6:41 
AnswerRe: Doesnt work with input string containing meta characters Pin
Rei Miyasaka1-Feb-06 19:03
Rei Miyasaka1-Feb-06 19:03 
AnswerRe: Doesnt work with input string containing meta characters PinPopular
Rei Miyasaka26-Mar-06 11:22
Rei Miyasaka26-Mar-06 11:22 
AnswerRe: Doesnt work with input string containing meta characters Pin
N3croman12-Jan-11 1:13
N3croman12-Jan-11 1:13 
QuestionA small improvement? Pin
Jim Parsells16-Sep-05 10:40
Jim Parsells16-Sep-05 10:40 
AnswerRe: A small improvement? Pin
Jim Parsells16-Sep-05 16:35
Jim Parsells16-Sep-05 16:35 
GeneralRe: A small improvement? Pin
Rei Miyasaka16-Sep-05 20:56
Rei Miyasaka16-Sep-05 20:56 
GeneralRe: A small improvement? Pin
Jim Parsells17-Sep-05 5:09
Jim Parsells17-Sep-05 5:09 
GeneralRe: A small improvement? Pin
Rei Miyasaka17-Sep-05 11:48
Rei Miyasaka17-Sep-05 11:48 
AnswerRe: A small improvement? Pin
Rei Miyasaka16-Sep-05 20:59
Rei Miyasaka16-Sep-05 20:59 
GeneraliNice trick :) Pin
Pop Catalin15-Sep-05 20:49
Pop Catalin15-Sep-05 20:49 
GeneralRe: iNice trick :) Pin
Rei Miyasaka16-Sep-05 21:14
Rei Miyasaka16-Sep-05 21:14 

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