grep.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Text.RegularExpressions;
using System.IO;

namespace grep
{
    class Program
    {
        static void Main(string[] args)
        {
            string joinedArgs = String.Join(" ", args);
            string[] splitArgs = joinedArgs.Split(';');

            List<string> lines = new List<string>();
            List<string> matchedLines = new List<string>();

            if (splitArgs.Length != 2)
            {
                Console.WriteLine("Invalid parameters.  Syntax: grep.exe pattern; file");
                return;
            }

            string pattern = splitArgs[0];
            string file = splitArgs[1];

            if (!File.Exists(file))
            {
                Console.WriteLine("Unable to find file '" + file + "'.");
                return;
            }

            lines = File.ReadAllLines(file).ToList<string>();

            matchedLines = GetMatchingLines(pattern, lines);

            foreach(string line in matchedLines)
            {
                Console.WriteLine(line);
            }

            Console.WriteLine("Found " + matchedLines.Count + " matching lines.");
        }

        /// <summary>
        /// Returns a string array containing the lines matching the provided wildcard in the provided string array
        /// </summary>
        /// <returns></returns>
        static List<string> GetMatchingLines(string wildcard, List<string> lines)
        {
            string pattern = WildcardToRegex(wildcard);
            List<string> retVal = new List<string>();

            foreach (string line in lines)
            {
                if (Regex.IsMatch(line, pattern))
                    retVal.Add(line);
            }
            return retVal;
        }

        /// <summary>
        /// Converts the specified wildcard pattern to a regular expression.
        /// </summary>
        /// <param name="pattern">The wildcard pattern to convert.</param>
        /// <returns>The regular expression resulting from the conversion.</returns>
        internal static string WildcardToRegex(string pattern = "")
        {
            return "^" + System.Text.RegularExpressions.Regex.Escape(pattern)
                              .Replace(@"\*", ".*")
                              .Replace(@"\?", ".")
                       + "$";
        }
    }
}