Ex, C# - rextester

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Microsoft (R) Visual C# Compiler version 2.9.0.63208 (958f2354)

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

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            Program p = new Program();
            string input = "c:\\Users\\Llama\\Desktop\\My.Very.Green_.0001.jpg";
            string output = p.GetNewName(input);
            Console.WriteLine(output);
        }

private static IReadOnlyDictionary<string, string> _mapping = new Dictionary<string, string>()
        {
            { "0001", "APPLE" },
            { "0002", "PEAR" }
        };

private string GetNewName(string originalFileName)
        {
            // if the path is c:\test\Green_.0001.jpg then we'll end up with filePath containing c:\test and fileName containing Green_.0001.jpg
            string filePath = Path.GetDirectoryName(originalFileName);
            string fileName = Path.GetFileName(originalFileName); // get only the name part

// Split the filename by .
            string[] parts = fileName.Split('.');

// If we have enough parts in the filename try and extract the id and replace it
            if (parts.Length >= 2)
            {
                // extract the id (e.g. 0001)
                string id = parts[parts.Length - 2];

// look it up in the mapping dictionary
                if (_mapping.TryGetValue(id, out var newName))
                {
                    // join everything up to the id (i.e. Green_)
                    string leftPart = string.Join(".", parts.Take(parts.Length - 2));
                    // Append the new name and the last part (the extension)
                    fileName = $"{leftPart}{newName}.{parts.Last()}";
                }
            }

// Recombine the filePath and fileName
            return Path.Combine(filePath, fileName);
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,47 sec, absolute running time: 0,13 sec, cpu time: 0,14 sec, average memory usage: 15 Mb, average nr of threads: 3, absolute service time: 0,6 sec