Build a regex pattern from dynamic folder path string

Question

I want to iterate folders with Directory.EnumerateDirectories and check if there are folders starting with a specific pattern in each path.

static void SearchFolder(string searchDirectory)
{
    foreach (var path in Directory.EnumerateDirectories(searchDirectory))
    {
        var pattern = folderName + @"\10.*";
        var isProjectFolderMatch = Regex.Match(path, pattern);

        if (isProjectFolderMatch.Success)
        {
            Console.WriteLine($"found: {path}");

        }
    }
}

But the regex match throws an error

'C:\Folder\10.*' - Reference to undefined group number 1.'

How can I build a dynamic pattern in this way?

Thanks!

Do you mean `@"10.*"` pattern? Note, that `\1` means "1st capturing group" in regular expressions — Dmitry Bychenko, Jun 27 '19 at 12:30
Yes, exactly. I want to attach the pattern to the end of the folderName variable — mottosson, Jun 27 '19 at 12:30
is that necessary to add the `foldername` into the pattern? since it is in the same `foldername` loop — LONG, Jun 27 '19 at 12:33
folderName might not be the best name, EnumerateDirectories return the full path, not just the folder name, so it looks more like "C:\Folder\SubFolder" not just "SubFolder" — mottosson, Jun 27 '19 at 12:34
To match a backslash with regex, it must be doubled. `@"\\1"` or `"\\\\1"` — Wiktor Stribiżew, Jun 27 '19 at 12:37

score 1 · Accepted Answer · answered Jun 27 '19 at 12:36

1

It seems, that you are looking for DirectoryInfo class: having, say, c:\MyData\MyPath\10folder you want to match 10 within 10folder. If it's your case:

static void SearchFolder(string searchDirectory) {
  var folders = Directory
    .EnumerateDirectories(searchDirectory)
    .Where(path => new DirectoryInfo(path).Name.StartsWith("10"));

  foreach (var folderName in folders)
    Console.WriteLine($"found: {folderName}");
}

In case you want regular expression, put it as

     .Where(path => Regex.IsMatch(new DirectoryInfo(path).Name, "10.*"));

Please, note that "10.*" pattern means starting from 10, when you original pattern @"\10.*" uses \1 which means 1st capturing group.

answered Jun 27 '19 at 12:36

Dmitry Bychenko

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It looked like the string had escaping backslash \\. Your suggestion didn't quite answer the direct question about how to build a dynamic path pattern, but it solved my problem. Thanks! – mottosson Jun 27 '19 at 13:24
@mottosson: please, note, that valid path can have *different* separators: `Path.AltDirectorySeparatorChar` and `Path.DirectorySeparatorChar`, e.g. `c:/MyData/MyPath/10folder` is a valid path.That's why hardcoding *back slash* can be a bad idea, when `DirectoryInfo` works with whatever separators – Dmitry Bychenko Jun 27 '19 at 13:27

Build a regex pattern from dynamic folder path string

1 Answers1