CLI ergonomics

using System;

// A tiny CLI that prints help if no args or -h/--help is passed.
public class Program
{
  static void PrintUsage()
  {
    Console.WriteLine("usage: tool -i <input> [-o <output>] [--verbose]");
    Console.WriteLine("options:");
    Console.WriteLine("  -i, --input     input file path (required)");
    Console.WriteLine("  -o, --output    output file path (optional)");
    Console.WriteLine("  -h, --help      show help");
    Console.WriteLine("      --verbose   print extra diagnostics to stderr");
  }

  public static void Main(string[] args)
  {
    if (args.Length == 0 || args[0] == "-h" || args[0] == "--help")
    {
      PrintUsage();
      Environment.ExitCode = 0;
      return;
    }

    Console.WriteLine("OK: arguments received"); // placeholder success
  }
}

using System;

// Minimal manual parsing for beginners (no external libs).
public class Program
{
  static void Error(string msg)
  {
    Console.Error.WriteLine("error: " + msg);
    Environment.ExitCode = 1; // non-zero means failure
  }

  public static void Main(string[] args)
  {
    string input = null;
    string output = null;

    for (int i = 0; i < args.Length; i++)
    {
      string a = args[i];
      if (a == "-i" || a == "--input")
      {
        if (i + 1 >= args.Length) { Error("missing value for " + a); return; }
        input = args[++i];
      }
      else if (a == "-o" || a == "--output")
      {
        if (i + 1 >= args.Length) { Error("missing value for " + a); return; }
        output = args[++i];
      }
      else if (a == "-h" || a == "--help")
      {
        Console.WriteLine("usage: tool -i <input> [-o <output>]");
        return;
      }
      else
      {
        Error("unknown option: " + a);
        return;
      }
    }

    if (input == null) { Error("input is required (-i)"); return; }

    // Success path: write result to stdout
    Console.WriteLine("Processed " + input + (output == null ? "" : (" -> " + output)));
    Environment.ExitCode = 0;
  }
}

using System;

// Show separation of streams: stdout (results) vs stderr (diagnostics).
public class Program
{
  public static void Main(string[] args)
  {
    bool verbose = false;
    for (int i = 0; i < args.Length; i++) if (args[i] == "--verbose") verbose = true;

    if (verbose) Console.Error.WriteLine("info: starting work");
    // pretend to compute a number
    int result = 42;
    // Result goes to stdout so it can be piped:  tool ... > out.txt
    Console.WriteLine(result);

    if (verbose) Console.Error.WriteLine("info: finished work");
    Environment.ExitCode = 0;
  }
}