How to get a substring with Regex in C#

Question

My program parses an XML-File which contains paths. Now I need to parse special folders like Appdata on different Windows devices:

<entry path="C:\Users\Simon\AppData\Roaming\myprogram" />

My attempt is to change the line into:

<entry path="#{APPDATA}\myprogram" />

and parse it using a Regular Expression:

string pattern = "#{ * }"; // what does fit here?

I've read some tutorials one Regex but I just can't figure out which Regex fits here.

How can I get the content between #{ and } using a regular Expression?

Why do you need regexp? If you have map of special paths that you want to change, simply string.Replace would do the job — Igoris
– Igoris, Commented Oct 6, 2015 at 14:23
@IgorisAzanovas And i wouldn't do this with a string containing the whole XML. Use the XMLDocument - Object to get the entry and modify it's "path" property. — Alex H
– Alex H, Commented Oct 6, 2015 at 14:26

poke · Accepted Answer · 2015-10-06 14:48:24Z

2

Just register general placeholders which you replace, e.g.

Dictionary<string, string> placeholders = new Dictionary<string, string>
{
    { "#{APPDATA}", @"C:\Users\Simon\AppData\Roaming" },
    { "#{SYSTEM32}", @"C:\Windows\System32" }
};

string ReplacePlaceholders (string text)
{
    foreach (var kv in placeholders)
    {
        text = text.Replace(kv.Key, kv.Value);
    }
    return text;
}

Used like this:

// this would come from the XML attribute
string path = @"#{APPDATA}\myprogram";

string newPath = ReplacePlaceholders(path);
Console.WriteLine(newPath); // C:\Users\Simon\AppData\Roaming\myprogram

As for actual values paths, you can also use Environment.GetFolderPath with the Environment.SpecialFolder enumeration to get the actual paths. But for the replacements and also other values, the answer still applies

Finally, since I wasn’t sure from your question in what direction you wanted to make these replacements, of course you can also reverse the mapping in above dictionary. I just assumed you had placeholders you wanted to replace by real paths.

edited Oct 6, 2015 at 14:48

answered Oct 6, 2015 at 14:28

poke

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1 Comment

James Over a year ago

Environment.SpecialFolder?

CodingWithSpike · Accepted Answer · 2015-10-06 14:37:23Z

1

You would want to use a match group in your regex. It would look like:

"#{(.*)}"

Then the Match.Groups property (documentation in the above link) would contain that "APPDATA" text.

This code prints "APPDATA" to the console

        var matches = Regex.Matches(@"#{APPDATA}\myprogram", "#{(.*)}");
        foreach (Match match in matches)
          Console.WriteLine(match.Groups[1].Value);

edited Oct 6, 2015 at 14:37

answered Oct 6, 2015 at 14:25

CodingWithSpike

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3 Comments

CodingWithSpike Over a year ago

For the record, I think @poke has a better solution to the overall problem, but I went for an answer to the specific question of getting the text from a match in regex. If I was implementing this behavior I would use poke's solution.

CodingWithSpike Over a year ago

@poke actually yes it is a valid regex. what is invalid about it? (unless you are talking about the surrounding quotes? The OP had it in a string assigned to a variable so I left the quotes in there)

poke Over a year ago

Odd, I was thinking that the unescaped curly braces (a quantifier in regexes) would break but apparently, C#’s implementation is smart enough not to parse them as quantifiers when they don’t contain a number range. Nevermind me then :)

Cetin Basoz · Accepted Answer · 2015-10-06 15:06:43Z

Reading your question once again, maybe it is the other way you are asking?

void Main()
{
  string myXML = @"
  <x>
  <paths>
  <entry path=""#{APPDATA}\myprogram"" />
  <entry path=""#{APPDATA}\yourprogram"" />
  <entry path=""#{APPDATA}\hisprogram"" />
  <entry path=""C:\OtherFolder\DummyProgram"" />
  <entry src=""C:\OtherFolder\DummyProgram"" />
  </paths>
  <Other>Other</Other>
  </x>";

  var appdata = Environment.GetFolderPath( 
    Environment.SpecialFolder.ApplicationData );
XDocument doc = XDocument.Parse(myXML);

  doc.Descendants("entry")
  .Where(xd => xd.Attribute("path") != null &&
      ((string)xd.Attribute("path")).StartsWith("#{APPDATA}"))
  .ToList()
  .ForEach(e => {
     var oldPath = (string)e.Attribute("path");
     var newPath = Path.Combine(appdata, Path.GetFileName(oldPath));
     e.Attribute("path").SetValue(newPath);
     } );

  Console.WriteLine( doc.ToString() );

}

Cetin Basoz · Accepted Answer · 2015-10-06 14:47:11Z

0

Wouldn't it be simpler to use Linq To XML for this. I couldn't see an exact pattern in your question, but probably something like this:

void Main()
{
  string myXML = @"
  <x>
  <paths>
  <entry path=""C:\Users\Simon\AppData\Roaming\myprogram"" />
  <entry path=""C:\Users\Simon\AppData\Roaming\yourprogram"" />
  <entry path=""C:\Users\Simon\AppData\Roaming\hisprogram"" />
  <entry path=""C:\OtherFolder\DummyProgram"" />
  <entry src=""C:\OtherFolder\DummyProgram"" />
  </paths>
  <Other>Other</Other>
  </x>";

XDocument doc = XDocument.Parse(myXML);

  doc.Descendants("entry")
  .Where(xd => xd.Attribute("path") != null &&
      ((string)xd.Attribute("path")).ToLower().Contains("appdata"))
  .ToList()
  .ForEach(e => {
     var oldPath = (string)e.Attribute("path");
     var newPath = @"#{APPDATA}\" + Path.GetFileName(oldPath);
     e.Attribute("path").SetValue(newPath);
     } );

  Console.WriteLine( doc.ToString() );

}

answered Oct 6, 2015 at 14:47

Cetin Basoz

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4 Comments

poke Over a year ago

What if my user name was appdata?

Cetin Basoz Over a year ago

What does it matter? It would get replaced.

poke Over a year ago

My point was mostly, that a path C:\Users\appdata\Documents\foo\bar\baz would be—incorreclty—replaced to #{APPDATA}\baz too.

Cetin Basoz Over a year ago

I don't think it would be incorrect. I don't see in original question that states he already does know the path. He says if there is "appdata" in path. Maybe I should just make that \appdata\ instead of just appdata. It would be "correctly" replaced IMHO.

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