如何为带有字母和数字的搜索模式创建正则表达式？

Question

I am trying to get all the folders inside a given path that match a pattern. The pattern I need is an H with a number that can go from 1 to 9 .

This is how I try to create a regular expression, but it crashes with an "Illegal pattern" exception:

Regex searchPattern = new Regex(@"(H\d +)\");

This is how I get the folders (paths):

List<string> folders = Directory.GetDirectories(path).Where(p => searchPattern.IsMatch(path)).ToList();

How can I create a proper regular expression that matches the letter H with a number?

Answer 1

Could you provide example input? If I run this:

var path = "H3";
var match = Regex.Match(path, "H[1-9]").Success;

if (match)
{
    Console.WriteLine("Match found!");
    Console.ReadKey();
}

I get "Match found!" in console. Although, I don't know what your exact input is. My answer is based purely on: "The pattern I need is an H with a number that can go from 1 to 9.".

Answer 2

I try to create the Regular Expression but it crashes (illegal pattern)

The problem you have is caused by the literal \\ that is at the end of the pattern. The backslash is an escaping symbol in a regex pattern, and must be followed with some char.

A pattern that matches H is H and a pattern that matches a digit from 1 to 9 is [1-9] (a positive character class). So, declare it as

var searchPattern = new Regex(@"H[1-9]");

Then, if you declare the variable as p in the lambda part, use p instead of path (the original directory you are searching for subfolders).

Answer 3

The following code should suit your needs. Please note your Lambda was using path instead of the argument p .

string path = "C:/my-path";
Regex searchPattern = new Regex(@"H\d");
List<string> folders = Directory.GetDirectories(path).Where(p => searchPattern.IsMatch(p)).ToList();