How can I combine regex with a string?

Question

I am fairly new to using regex and I am not entirely clear on the syntax for everything yet. Basically I am stuck on a bit of code where I have:

if(@"\d{2,}\s"+string == Path.GetFileNameWithoutExtension(dir)) 
{ 
    do stuff 
}

My problem is that it won't match anything. I basically have a bunch of files that it's searching through that all have 2 digits and a space, then the name that the user is searching for. Can I combine regex + string like that or is the problem with my regex/statement? Just for clarity, it will match when I actually remove the two digits and space from the files. I apologize if the problem is obvious, I've only been playing with regex for a few days...

String == doesn't have anything to do with regexes. It will just do a literal text compare. You need to use Regex.IsMatch or Regex.Matches to compare a string with a regex, not == — Pete Baughman
– Pete Baughman, Commented Mar 28, 2014 at 22:48
No. If that were valid syntactically (which it isn't), that does nothing to evaluate the regular expression. It would simply concatenate \d{2,}\s and the content of string into a single string - what you call a "regex" would be simply a literal string. Instead of trying to hack a regex into things (which isn't always appropriate), why not explain what you're trying to accomplish and ask how to to so? — Ken White
– Ken White, Commented Mar 28, 2014 at 22:49
If you want a string to be considered as a part of a regular expression, strings can be matched as literals within the regex. Example: \d{3}pie will match any three digits and the word pie. — signus
– signus, Commented Mar 28, 2014 at 23:05

p.s.w.g · Accepted Answer · 2014-03-28 22:49:03Z

3

Your if statement is not attempting to match a regular expression pattern, it's simply comparing two strings. That's what the Regex.IsMatch method is for. Also you will probably want to use Regex.Escape to combine a regex pattern with an arbitrary string.

Try this:

using System.Text.RegularExpressions;

...

var pattern = @"\d{2,}\s" + Regex.Escape(myString);
var fileName = Path.GetFileNameWithoutExtension(dir);
if (Regex.IsMatch(fileName, pattern))
{ 
    // do stuff 
}

answered Mar 28, 2014 at 22:49

p.s.w.g

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Greg · Accepted Answer · 2014-03-28 23:11:36Z

You actually shouldn't have to use a Regular Expression in that instance, in fact that may be over complicating the goal.

string path = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData);
string [] file = Directory.GetFiles(path, @"11_*.txt", SearchOption.AllDirectories);
foreach(string f in file)
{
    // Do Something.
}

If your entirely headset on utilizing Regular Expressions, you would do something more along these lines:

using System.Text.RegularExpressions;

...

    string path = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData);
    var file = Regex.IsMatch(path, @"\d{2,}\2");
    if(file == true)
    {
         // Do Something
    }

That is one way to use Regular Expressions, they can be even more powerful with Linq. I would highly recommend researching this on the MSDN, it has some solid resources.

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