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?

Why do you have pairs of escaped double-quotes in `"()"`? This will result in a regex pattern `()` - certainly not what you want... — , Aug 06 '14 at 01:21

score 1 · Answer 1 · answered Aug 06 '14 at 02:49

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 ;
  }) ;

score 0 · Accepted Answer · answered Aug 06 '14 at 01:16

0

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" + @""".*?>)";

answered Aug 06 '14 at 01:16

rfernandes

1,121
7
9

I guess that's what happens when you haven't had much sleep in one day. So close and yet so far. thanks, mate. – coson Aug 06 '14 at 16:29

Regex.Match Parameter Possible?

2 Answers2