Regex.Match Parameter Possible?

Question

Good Day,

I have some HTML input that I want to do a search and replace operation.

string html = @"
    <div class=""left bottom-margin"">
    <input id=""0086"" maxlength=""29"" data-src=""200:80"" type=""text""><br />
    <input id=""0087"" maxlength=""38"" data-src=""201:80"" type=""text""><br />
    <input id=""0088"" maxlength=""38"" data-src=""202:80"" type=""text""><br />
</div>";    

// Here we call Regex.Match.
Match match = Regex.Match(html, @"(<input.*id=""0087"".*?>)", RegexOptions.IgnoreCase);

// Here we check the Match instance.
if (match.Success)
{
    // Finally, we get the Group value and display it.
    string key = match.Groups[1].Value;
    Console.WriteLine(key);
} else {
    Console.WriteLine("No Match...");
}

This code does work, so far, but I want to be able to provide a parameter to the Regex.Match initialization. Is this possible? What if I wanted to search for 0086 or 0088 as the id? I have a couple hundred tags like this where I want to be able to find the HTML tag by providing a parameter?

I understand that the @ makes the string verbatim.

But I've tried doing this:

// string pattern = "(<input.*id=\"\"0087\"\".*?>)";
// string pattern = "(<input.*id=\"\"" + "0087" + "\"\".*?>)";

This doesn't work either. Most of the Regex.Match samples I've seen use the @ verbatim symbol to do the actual matching. Is my understanding of this correct?

Any suggestions?

Answer 1

You can't supply a parameter to a regular expression. But you could...Not try to coerce regular expressions into being an HTML parser.

• If your document contains valid markup, you can load it into a suitable XMLDocument and apply the desired tranformations in any of a number of different ways:
  • either programatically using XPATH queries
  • by traversing the document to find the nodes you're interested in,
  • applying an XSLT transformation.
  • using Linq for XML
• OR you could install the HTML Agility Pack via NuGet , load your document into an HTmlDocument and use its transformation capabilities.

If you're determined to use regular expression, you can

• Build your regular expression on the fly, something like

   Regex ConstructRegex( int id ) { string pattern = string.format( @"(<input.*id=""{0:0000}"".*?>)" , id ) ; Regex instance = new Regex( pattern ) ; return instance } 

• Make your regular expression generic and supply a MatchEvaluator / Func<Match,string> to apply the desired transformations to each match (if required):

   static readonly Regex rx = new Regex( @"(<input.*id=""(?<id>\\d\\d\\d\\d)"".*?>)" ) ; string Transform( string html , Func<string,string> transform ) { string transformed = rx.Replace( html, transform ) ; return transformed ; } 

  Which you could use thus:

   string raw = "some html here" ; string cooked = Transform( raw , m => { int id = int.Parse( m.Groups["id"].Value ) ; string s = Match.Value ; if ( id == 86 ) { s = apply_some_transformation_here(m.Value) ; } return s ; }) ; 

Answer 2

How about this:

string pattern = String.Format(@"(<input.*id=""{0}"".*?>)", "0087");

It looks like it works fine for me.

Actually, even this works as well:

string pattern = @"(<input.*id=""" + "0087" + @""".*?>)";