A very simple parser for loading .env files in a c# application. Has no external dependencies and supports basic references.

DotEnv.cs

namespace DotEnv
{
	public class DotEnv(ILogger<DotEnv> logger)
	{
		/// <summary>
		/// Holds a set of all environment variables set from .env files. Listed if logLevel set do debug.
		/// </summary>
		private readonly IDictionary<string, string> _finalEnvironmentVariables = new Dictionary<string, string>();

		private void LoadAndParse()
		{
			string currentDirectory = Directory.GetCurrentDirectory();
			logger.LogDebug("Working directory: {CurrentDirectory}", currentDirectory);
			var allEnvFiles = FindEnvFilesInDirectoryTree(currentDirectory);

			foreach (var envFile in allEnvFiles)
			{
				logger.LogDebug("Parsing env file: {EnvFile}", envFile);
				ParseEnvFile(envFile);
			}

			var allEnvVariables = _finalEnvironmentVariables.Select((keyValuePair) => $"{keyValuePair.Key}={keyValuePair.Value}");
			logger.LogDebug("Environment variables loaded:\n{EnvironmentVariables}", string.Join('\n', allEnvVariables));
		}

		/// <summary>
		/// Locates all .env* files in the specified directory and the set number of ancestors up to the root directory of the volume. Orders them so that the most specific files are loaded last.
		/// </summary>
		/// <param name="startingDirectory">Where to begin looking for env files</param>
		/// <param name="nrOfAncestorsToCheck">The number of ancestor directories to check (default = 20) up to the root directory. Set to 0 to only check current startingDirectory</param>
		/// <returns>A list of absolute file paths to all env files found orderer from least to most specific.</returns>
		private static List<string> FindEnvFilesInDirectoryTree(string startingDirectory, int nrOfAncestorsToCheck = 20) {
			string? currentDirectory = startingDirectory;
			var allFiles = new List<string>();
			while (nrOfAncestorsToCheck-- >= 0 && currentDirectory is not null)
			{
				var currentDirectoryFiles = Directory.GetFiles(currentDirectory, ".env*", SearchOption.TopDirectoryOnly);
				allFiles.AddRange(currentDirectoryFiles);
				currentDirectory = Directory.GetParent(currentDirectory)?.FullName;
			}
	
			allFiles.Sort();
			return allFiles;
		}

		private void ParseEnvFile(string filePath)
		{
			foreach (var line in File.ReadAllLines(filePath))
			{
				var parts = line.Trim().Split("=", StringSplitOptions.RemoveEmptyEntries);
				if (parts.Length < 2) continue;
				var name = parts[0];
				var value = parts[1];

				if (value.StartsWith('$'))
				{
					var referenceEnvironmentVariableName = value[1..];
					// This value is a reference to another environment variable that must be resolved.
					logger.LogDebug("Resolving reference {Value} in {Name}", referenceEnvironmentVariableName, name);
					value = Environment.GetEnvironmentVariable(referenceEnvironmentVariableName);
				}

				logger.LogDebug("Setting environment variable {Name} to {Value}", name, value);
				_finalEnvironmentVariables[name] = value ?? "";
				Environment.SetEnvironmentVariable(name, value);
			}
		}

		/// <summary>
		/// Set up and load environment variables from any .env file.
		/// </summary>
		public static void LoadDotEnv(LogLevel logLevel = LogLevel.Information)
		{
			var logger = LoggerFactory.Create(builder =>
			{
				builder.AddConsole();
				builder.SetMinimumLevel(logLevel);
			}).CreateLogger<DotEnv>();
			var env = new DotEnv(logger);
			env.LoadAndParse();
		}
	}
}