Update version

Closes #19

.gitignore

@@ -143,6 +143,7 @@ _TeamCity*
 _NCrunch_*
 .*crunch*.local.xml
 nCrunchTemp_*
+.ncrunchsolution
 
 # MightyMoose
 *.mm.*

CliFx.Benchmarks/Benchmark.cs

@@ -8,7 +8,7 @@ namespace CliFx.Benchmarks
     [RankColumn]
     public class Benchmark
     {
-        private static readonly string[] Arguments = { "--str", "hello world", "-i", "13", "-b" };
+        private static readonly string[] Arguments = {"--str", "hello world", "-i", "13", "-b"};
 
         [Benchmark(Description = "CliFx", Baseline = true)]
         public Task<int> ExecuteWithCliFx() => new CliApplicationBuilder().AddCommand(typeof(CliFxCommand)).Build().RunAsync(Arguments);
@@ -19,16 +19,17 @@ namespace CliFx.Benchmarks
         [Benchmark(Description = "McMaster.Extensions.CommandLineUtils")]
         public int ExecuteWithMcMaster() => McMaster.Extensions.CommandLineUtils.CommandLineApplication.Execute<McMasterCommand>(Arguments);
 
-        // Skipped because this benchmark freezes after a couple of iterations
-        // Probably wasn't designed to run multiple times in single process execution
-        //[Benchmark(Description = "CommandLineParser")]
+        [Benchmark(Description = "CommandLineParser")]
         public void ExecuteWithCommandLineParser()
         {
-            var parsed = CommandLine.Parser.Default.ParseArguments(Arguments, typeof(CommandLineParserCommand));
+            var parsed = new CommandLine.Parser().ParseArguments(Arguments, typeof(CommandLineParserCommand));
             CommandLine.ParserResultExtensions.WithParsed<CommandLineParserCommand>(parsed, c => c.Execute());
         }
 
         [Benchmark(Description = "PowerArgs")]
         public void ExecuteWithPowerArgs() => PowerArgs.Args.InvokeMain<PowerArgsCommand>(Arguments);
+
+        [Benchmark(Description = "Clipr")]
+        public void ExecuteWithClipr() => clipr.CliParser.Parse<CliprCommand>(Arguments).Execute();
     }
 }

CliFx.Benchmarks/CliFx.Benchmarks.csproj

@@ -2,12 +2,12 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp2.2</TargetFramework>
-    <LangVersion>latest</LangVersion>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
     <PackageReference Include="BenchmarkDotNet" Version="0.11.5" />
+    <PackageReference Include="clipr" Version="1.6.1" />
     <PackageReference Include="CommandLineParser" Version="2.6.0" />
     <PackageReference Include="McMaster.Extensions.CommandLineUtils" Version="2.3.4" />
     <PackageReference Include="PowerArgs" Version="3.6.0" />

CliFx.Benchmarks/Commands/CliFxCommand.cs

@@ -1,4 +1,5 @@
-using System.Threading.Tasks;
+using System.Threading;
+using System.Threading.Tasks;
 using CliFx.Attributes;
 using CliFx.Services;
 

CliFx.Benchmarks/Commands/CliprCommand.cs

@@ -0,0 +1,20 @@
+using clipr;
+
+namespace CliFx.Benchmarks.Commands
+{
+    public class CliprCommand
+    {
+        [NamedArgument('s', "str")]
+        public string StrOption { get; set; }
+
+        [NamedArgument('i', "int")]
+        public int IntOption { get; set; }
+
+        [NamedArgument('b', "bool", Constraint = NumArgsConstraint.Optional, Const = true)]
+        public bool BoolOption { get; set; }
+
+        public void Execute()
+        {
+        }
+    }
+}

CliFx.Demo/CliFx.Demo.csproj

@@ -2,8 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp2.2</TargetFramework>
-    <LangVersion>latest</LangVersion>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>

CliFx.Demo/Commands/BookAddCommand.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Threading;
 using System.Threading.Tasks;
 using CliFx.Attributes;
 using CliFx.Demo.Internal;

CliFx.Demo/Commands/BookCommand.cs

@@ -1,4 +1,5 @@
-using System.Threading.Tasks;
+using System.Threading;
+using System.Threading.Tasks;
 using CliFx.Attributes;
 using CliFx.Demo.Internal;
 using CliFx.Demo.Services;

CliFx.Demo/Commands/BookListCommand.cs

@@ -1,4 +1,5 @@
-using System.Threading.Tasks;
+using System.Threading;
+using System.Threading.Tasks;
 using CliFx.Attributes;
 using CliFx.Demo.Internal;
 using CliFx.Demo.Services;

CliFx.Demo/Commands/BookRemoveCommand.cs

@@ -1,4 +1,5 @@
-using System.Threading.Tasks;
+using System.Threading;
+using System.Threading.Tasks;
 using CliFx.Attributes;
 using CliFx.Demo.Services;
 using CliFx.Exceptions;

CliFx.Tests.Dummy/CliFx.Tests.Dummy.csproj

@@ -1,14 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-
-  <PropertyGroup>
-    <OutputType>Exe</OutputType>
-    <TargetFramework>net46</TargetFramework>
-    <Version>1.2.3.4</Version>
-    <LangVersion>latest</LangVersion>
-  </PropertyGroup>
-
-  <ItemGroup>
-    <ProjectReference Include="..\CliFx\CliFx.csproj" />
-  </ItemGroup>
-
-</Project>

CliFx.Tests.Dummy/Commands/GreeterCommand.cs

@@ -1,31 +0,0 @@
-using System.Text;
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Services;
-
-namespace CliFx.Tests.Dummy.Commands
-{
-    [Command]
-    public class GreeterCommand : ICommand
-    {
-        [CommandOption("target", 't', Description = "Greeting target.")]
-        public string Target { get; set; } = "world";
-
-        [CommandOption('e', Description = "Whether the greeting should be exclaimed.")]
-        public bool IsExclaimed { get; set; }
-
-        public Task ExecuteAsync(IConsole console)
-        {
-            var buffer = new StringBuilder();
-
-            buffer.Append("Hello").Append(' ').Append(Target);
-
-            if (IsExclaimed)
-                buffer.Append('!');
-
-            console.Output.WriteLine(buffer.ToString());
-
-            return Task.CompletedTask;
-        }
-    }
-}

CliFx.Tests.Dummy/Commands/LogCommand.cs

@@ -1,25 +0,0 @@
-using System;
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Services;
-
-namespace CliFx.Tests.Dummy.Commands
-{
-    [Command("log", Description = "Calculate the logarithm of a value.")]
-    public class LogCommand : ICommand
-    {
-        [CommandOption("value", 'v', IsRequired = true, Description = "Value whose logarithm is to be found.")]
-        public double Value { get; set; }
-
-        [CommandOption("base", 'b', Description = "Logarithm base.")]
-        public double Base { get; set; } = 10;
-
-        public Task ExecuteAsync(IConsole console)
-        {
-            var result = Math.Log(Value, Base);
-            console.Output.WriteLine(result);
-
-            return Task.CompletedTask;
-        }
-    }
-}

CliFx.Tests.Dummy/Commands/SumCommand.cs

@@ -1,23 +0,0 @@
-using System.Collections.Generic;
-using System.Linq;
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Services;
-
-namespace CliFx.Tests.Dummy.Commands
-{
-    [Command("sum", Description = "Calculate the sum of all input values.")]
-    public class SumCommand : ICommand
-    {
-        [CommandOption("values", 'v', IsRequired = true, Description = "Input values.")]
-        public IReadOnlyList<double> Values { get; set; }
-
-        public Task ExecuteAsync(IConsole console)
-        {
-            var result = Values.Sum();
-            console.Output.WriteLine(result);
-
-            return Task.CompletedTask;
-        }
-    }
-}

CliFx.Tests.Dummy/Program.cs

@@ -1,21 +0,0 @@
-using System.Globalization;
-using System.Threading.Tasks;
-
-namespace CliFx.Tests.Dummy
-{
-    public static class Program
-    {
-        public static Task<int> Main(string[] args)
-        {
-            // Set culture to invariant to maintain consistent format because we rely on it in tests
-            CultureInfo.DefaultThreadCurrentCulture = CultureInfo.InvariantCulture;
-            CultureInfo.DefaultThreadCurrentUICulture = CultureInfo.InvariantCulture;
-
-            return new CliApplicationBuilder()
-                .AddCommandsFromThisAssembly()
-                .UseDescription("Dummy program used for E2E tests.")
-                .Build()
-                .RunAsync(args);
-        }
-    }
-}

CliFx.Tests/CliApplicationBuilderTests.cs

@@ -0,0 +1,51 @@
+using NUnit.Framework;
+using System;
+using System.IO;
+using CliFx.Services;
+using CliFx.Tests.Stubs;
+using CliFx.Tests.TestCommands;
+
+namespace CliFx.Tests
+{
+    [TestFixture]
+    public class CliApplicationBuilderTests
+    {
+        // Make sure all builder methods work
+        [Test]
+        public void All_Smoke_Test()
+        {
+            // Arrange
+            var builder = new CliApplicationBuilder();
+
+            // Act
+            builder
+                .AddCommand(typeof(HelloWorldDefaultCommand))
+                .AddCommandsFrom(typeof(HelloWorldDefaultCommand).Assembly)
+                .AddCommands(new[] { typeof(HelloWorldDefaultCommand) })
+                .AddCommandsFrom(new[] { typeof(HelloWorldDefaultCommand).Assembly })
+                .AddCommandsFromThisAssembly()
+                .AllowDebugMode()
+                .AllowPreviewMode()
+                .UseTitle("test")
+                .UseExecutableName("test")
+                .UseVersionText("test")
+                .UseDescription("test")
+                .UseConsole(new VirtualConsole(TextWriter.Null))
+                .UseCommandFactory(schema => (ICommand)Activator.CreateInstance(schema.Type))
+                .UseCommandOptionInputConverter(new CommandOptionInputConverter())
+                .UseEnvironmentVariablesProvider(new EnvironmentVariablesProviderStub())
+                .Build();
+        }
+
+        // Make sure builder can produce an application with no parameters specified
+        [Test]
+        public void Build_Test()
+        {
+            // Arrange
+            var builder = new CliApplicationBuilder();
+
+            // Act
+            builder.Build();
+        }
+    }
+}

CliFx.Tests/CliApplicationTests.Commands.cs

@@ -1,53 +0,0 @@
-using System;
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Exceptions;
-using CliFx.Services;
-
-namespace CliFx.Tests
-{
-    public partial class CliApplicationTests
-    {
-        [Command]
-        private class DefaultCommand : ICommand
-        {
-            public Task ExecuteAsync(IConsole console)
-            {
-                console.Output.WriteLine("DefaultCommand executed.");
-                return Task.CompletedTask;
-            }
-        }
-
-        [Command("cmd")]
-        private class NamedCommand : ICommand
-        {
-            public Task ExecuteAsync(IConsole console)
-            {
-                console.Output.WriteLine("NamedCommand executed.");
-                return Task.CompletedTask;
-            }
-        }
-    }
-
-    // Negative
-    public partial class CliApplicationTests
-    {
-        [Command("faulty1")]
-        private class FaultyCommand1 : ICommand
-        {
-            public Task ExecuteAsync(IConsole console) => throw new CommandException(150);
-        }
-
-        [Command("faulty2")]
-        private class FaultyCommand2 : ICommand
-        {
-            public Task ExecuteAsync(IConsole console) => throw new CommandException("FaultyCommand2 error message.", 150);
-        }
-
-        [Command("faulty3")]
-        private class FaultyCommand3 : ICommand
-        {
-            public Task ExecuteAsync(IConsole console) => throw new Exception("FaultyCommand3 error message.");
-        }
-    }
-}

CliFx.Tests/CliApplicationTests.cs

@@ -1,76 +1,123 @@
-using System;
+using FluentAssertions;
+using NUnit.Framework;
+using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Threading;
 using System.Threading.Tasks;
 using CliFx.Services;
-using FluentAssertions;
-using NUnit.Framework;
+using CliFx.Tests.Stubs;
+using CliFx.Tests.TestCommands;
 
 namespace CliFx.Tests
 {
     [TestFixture]
-    public partial class CliApplicationTests
+    public class CliApplicationTests
     {
+        private const string TestVersionText = "v1.0";
+
         private static IEnumerable<TestCaseData> GetTestCases_RunAsync()
         {
             yield return new TestCaseData(
-                new[] {typeof(DefaultCommand)},
+                new[] { typeof(HelloWorldDefaultCommand) },
                 new string[0],
-                "DefaultCommand executed."
+                "Hello world."
             );
 
             yield return new TestCaseData(
-                new[] {typeof(NamedCommand)},
-                new[] {"cmd"},
-                "NamedCommand executed."
-            );
-        }
-
-        private static IEnumerable<TestCaseData> GetTestCases_HelpAndVersion_RunAsync()
-        {
-            yield return new TestCaseData(
-                new[] {typeof(DefaultCommand)},
-                new string[0]
+                new[] { typeof(ConcatCommand) },
+                new[] { "concat", "-i", "foo", "-i", "bar", "-s", " " },
+                "foo bar"
             );
 
             yield return new TestCaseData(
-                new[] {typeof(DefaultCommand)},
-                new[] {"-h"}
+                new[] { typeof(ConcatCommand) },
+                new[] { "concat", "-i", "one", "two", "three", "-s", ", " },
+                "one, two, three"
             );
 
             yield return new TestCaseData(
-                new[] {typeof(DefaultCommand)},
-                new[] {"--help"}
+                new[] { typeof(DivideCommand) },
+                new[] { "div", "-D", "24", "-d", "8" },
+                "3"
             );
 
             yield return new TestCaseData(
-                new[] {typeof(DefaultCommand)},
-                new[] {"--version"}
+                new[] { typeof(HelloWorldDefaultCommand) },
+                new[] { "--version" },
+                TestVersionText
             );
 
             yield return new TestCaseData(
-                new[] {typeof(NamedCommand)},
-                new string[0]
+                new[] { typeof(ConcatCommand) },
+                new[] { "--version" },
+                TestVersionText
             );
 
             yield return new TestCaseData(
-                new[] {typeof(NamedCommand)},
-                new[] {"cmd", "-h"}
+                new[] { typeof(HelloWorldDefaultCommand) },
+                new[] { "-h" },
+                null
             );
 
             yield return new TestCaseData(
-                new[] {typeof(FaultyCommand1)},
-                new[] {"faulty1", "-h"}
+                new[] { typeof(HelloWorldDefaultCommand) },
+                new[] { "--help" },
+                null
             );
 
             yield return new TestCaseData(
-                new[] {typeof(FaultyCommand2)},
-                new[] {"faulty2", "-h"}
+                new[] { typeof(ConcatCommand) },
+                new string[0],
+                null
             );
 
             yield return new TestCaseData(
-                new[] {typeof(FaultyCommand3)},
-                new[] {"faulty3", "-h"}
+                new[] { typeof(ConcatCommand) },
+                new[] { "-h" },
+                null
+            );
+
+            yield return new TestCaseData(
+                new[] { typeof(ConcatCommand) },
+                new[] { "--help" },
+                null
+            );
+
+            yield return new TestCaseData(
+                new[] { typeof(ConcatCommand) },
+                new[] { "concat", "-h" },
+                null
+            );
+
+            yield return new TestCaseData(
+                new[] { typeof(ExceptionCommand) },
+                new[] { "exc", "-h" },
+                null
+            );
+
+            yield return new TestCaseData(
+                new[] { typeof(CommandExceptionCommand) },
+                new[] { "exc", "-h" },
+                null
+            );
+
+            yield return new TestCaseData(
+                new[] { typeof(ConcatCommand) },
+                new[] { "[preview]" },
+                null
+            );
+
+            yield return new TestCaseData(
+                new[] { typeof(ExceptionCommand) },
+                new[] { "exc", "[preview]" },
+                null
+            );
+
+            yield return new TestCaseData(
+                new[] { typeof(ConcatCommand) },
+                new[] { "concat", "[preview]", "-o", "value" },
+                null
             );
         }
 
@@ -78,96 +125,138 @@ namespace CliFx.Tests
         {
             yield return new TestCaseData(
                 new Type[0],
-                new string[0]
+                new string[0],
+                null, null
             );
 
             yield return new TestCaseData(
-                new[] {typeof(DefaultCommand)},
-                new[] {"non-existing"}
+                new[] { typeof(ConcatCommand) },
+                new[] { "non-existing" },
+                null, null
             );
 
             yield return new TestCaseData(
-                new[] {typeof(FaultyCommand1)},
-                new[] {"faulty1"}
+                new[] { typeof(ExceptionCommand) },
+                new[] { "exc" },
+                null, null
             );
 
             yield return new TestCaseData(
-                new[] {typeof(FaultyCommand2)},
-                new[] {"faulty2"}
+                new[] { typeof(CommandExceptionCommand) },
+                new[] { "exc" },
+                null, null
             );
 
             yield return new TestCaseData(
-                new[] {typeof(FaultyCommand3)},
-                new[] {"faulty3"}
+                new[] { typeof(CommandExceptionCommand) },
+                new[] { "exc" },
+                null, null
+            );
+
+            yield return new TestCaseData(
+                new[] { typeof(CommandExceptionCommand) },
+                new[] { "exc", "-m", "foo bar" },
+                "foo bar", null
+            );
+
+            yield return new TestCaseData(
+                new[] { typeof(CommandExceptionCommand) },
+                new[] { "exc", "-m", "foo bar", "-c", "666" },
+                "foo bar", 666
             );
         }
 
         [Test]
         [TestCaseSource(nameof(GetTestCases_RunAsync))]
-        public async Task RunAsync_Test(IReadOnlyList<Type> commandTypes, IReadOnlyList<string> commandLineArguments, string expectedStdOut)
+        public async Task RunAsync_Test(IReadOnlyList<Type> commandTypes, IReadOnlyList<string> commandLineArguments,
+            string expectedStdOut = null)
         {
             // Arrange
-            using (var stdout = new StringWriter())
+            using (var stdoutStream = new StringWriter())
             {
-                var console = new VirtualConsole(stdout);
+                var console = new VirtualConsole(stdoutStream);
+                var environmentVariablesProvider = new EnvironmentVariablesProviderStub();
 
                 var application = new CliApplicationBuilder()
                     .AddCommands(commandTypes)
+                    .UseVersionText(TestVersionText)
                     .UseConsole(console)
+                    .UseEnvironmentVariablesProvider(environmentVariablesProvider)
                     .Build();
 
                 // Act
                 var exitCode = await application.RunAsync(commandLineArguments);
+                var stdOut = stdoutStream.ToString().Trim();
 
                 // Assert
                 exitCode.Should().Be(0);
-                stdout.ToString().Trim().Should().Be(expectedStdOut);
-            }
-        }
 
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_HelpAndVersion_RunAsync))]
-        public async Task RunAsync_HelpAndVersion_Test(IReadOnlyList<Type> commandTypes, IReadOnlyList<string> commandLineArguments)
-        {
-            // Arrange
-            using (var stdout = new StringWriter())
-            {
-                var console = new VirtualConsole(stdout);
-
-                var application = new CliApplicationBuilder()
-                    .AddCommands(commandTypes)
-                    .UseConsole(console)
-                    .Build();
-
-                // Act
-                var exitCode = await application.RunAsync(commandLineArguments);
-
-                // Assert
-                exitCode.Should().Be(0);
-                stdout.ToString().Should().NotBeNullOrWhiteSpace();
+                if (expectedStdOut != null)
+                    stdOut.Should().Be(expectedStdOut);
+                else
+                    stdOut.Should().NotBeNullOrWhiteSpace();
             }
         }
 
         [Test]
         [TestCaseSource(nameof(GetTestCases_RunAsync_Negative))]
-        public async Task RunAsync_Negative_Test(IReadOnlyList<Type> commandTypes, IReadOnlyList<string> commandLineArguments)
+        public async Task RunAsync_Negative_Test(IReadOnlyList<Type> commandTypes, IReadOnlyList<string> commandLineArguments,
+            string expectedStdErr = null, int? expectedExitCode = null)
         {
             // Arrange
-            using (var stderr = new StringWriter())
+            using (var stderrStream = new StringWriter())
             {
-                var console = new VirtualConsole(TextWriter.Null, stderr);
+                var console = new VirtualConsole(TextWriter.Null, stderrStream);
+                var environmentVariablesProvider = new EnvironmentVariablesProviderStub();
 
                 var application = new CliApplicationBuilder()
                     .AddCommands(commandTypes)
+                    .UseVersionText(TestVersionText)
+                    .UseEnvironmentVariablesProvider(environmentVariablesProvider)
                     .UseConsole(console)
                     .Build();
 
                 // Act
                 var exitCode = await application.RunAsync(commandLineArguments);
+                var stderr = stderrStream.ToString().Trim();
 
                 // Assert
-                exitCode.Should().NotBe(0);
-                stderr.ToString().Should().NotBeNullOrWhiteSpace();
+                if (expectedExitCode != null)
+                    exitCode.Should().Be(expectedExitCode);
+                else
+                    exitCode.Should().NotBe(0);
+
+                if (expectedStdErr != null)
+                    stderr.Should().Be(expectedStdErr);
+                else
+                    stderr.Should().NotBeNullOrWhiteSpace();
+            }
+        }
+
+        [Test]
+        public async Task RunAsync_Cancellation_Test()
+        {
+            // Arrange
+            using (var stdoutStream = new StringWriter())
+            using (var cancellationTokenSource = new CancellationTokenSource())
+            {
+                var console = new VirtualConsole(stdoutStream, cancellationTokenSource.Token);
+                
+                var application = new CliApplicationBuilder()
+                    .AddCommand(typeof(CancellableCommand))
+                    .UseConsole(console)
+                    .Build();
+                var args = new[] { "cancel" };
+
+                // Act
+                var runTask = application.RunAsync(args);
+                cancellationTokenSource.Cancel();
+                var exitCode = await runTask.ConfigureAwait(false);
+                var stdOut = stdoutStream.ToString().Trim();
+
+                // Assert
+                exitCode.Should().Be(-2146233029);
+                stdOut.Should().Be("Printed");
             }
         }
     }

CliFx.Tests/CliFx.Tests.csproj

@@ -7,7 +7,6 @@
     <CollectCoverage>true</CollectCoverage>
     <CoverletOutputFormat>opencover</CoverletOutputFormat>
     <CoverletOutput>bin/$(Configuration)/Coverage.xml</CoverletOutput>
-    <LangVersion>latest</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>
@@ -15,7 +14,6 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.2.0" />
     <PackageReference Include="NUnit" Version="3.12.0" />
     <PackageReference Include="NUnit3TestAdapter" Version="3.14.0" />
-    <PackageReference Include="CliWrap" Version="2.3.1" />
     <PackageReference Include="coverlet.msbuild" Version="2.6.3">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
@@ -23,7 +21,6 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="..\CliFx.Tests.Dummy\CliFx.Tests.Dummy.csproj" />
     <ProjectReference Include="..\CliFx\CliFx.csproj" />
   </ItemGroup>
 

CliFx.Tests/CommandFactoryTests.Commands.cs

@@ -1,15 +0,0 @@
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Services;
-
-namespace CliFx.Tests
-{
-    public partial class CommandFactoryTests
-    {
-        [Command]
-        private class TestCommand : ICommand
-        {
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-    }
-}

CliFx.Tests/CommandInitializerTests.Commands.cs

@@ -1,21 +0,0 @@
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Services;
-
-namespace CliFx.Tests
-{
-    public partial class CommandInitializerTests
-    {
-        [Command]
-        private class TestCommand : ICommand
-        {
-            [CommandOption("int", 'i', IsRequired = true)]
-            public int IntOption { get; set; } = 24;
-
-            [CommandOption("str", 's')]
-            public string StringOption { get; set; } = "foo bar";
-
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-    }
-}

CliFx.Tests/CommandInitializerTests.cs

@@ -1,96 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using CliFx.Exceptions;
-using CliFx.Models;
-using CliFx.Services;
-using FluentAssertions;
-using NUnit.Framework;
-
-namespace CliFx.Tests
-{
-    [TestFixture]
-    public partial class CommandInitializerTests
-    {
-        private static CommandSchema GetCommandSchema(Type commandType) =>
-            new CommandSchemaResolver().GetCommandSchemas(new[] {commandType}).Single();
-
-        private static IEnumerable<TestCaseData> GetTestCases_InitializeCommand()
-        {
-            yield return new TestCaseData(
-                new TestCommand(),
-                GetCommandSchema(typeof(TestCommand)),
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("int", "13")
-                }),
-                new TestCommand {IntOption = 13}
-            );
-
-            yield return new TestCaseData(
-                new TestCommand(),
-                GetCommandSchema(typeof(TestCommand)),
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("int", "13"),
-                    new CommandOptionInput("str", "hello world")
-                }),
-                new TestCommand {IntOption = 13, StringOption = "hello world"}
-            );
-
-            yield return new TestCaseData(
-                new TestCommand(),
-                GetCommandSchema(typeof(TestCommand)),
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("i", "13")
-                }),
-                new TestCommand {IntOption = 13}
-            );
-        }
-
-        private static IEnumerable<TestCaseData> GetTestCases_InitializeCommand_Negative()
-        {
-            yield return new TestCaseData(
-                new TestCommand(),
-                GetCommandSchema(typeof(TestCommand)),
-                CommandInput.Empty
-            );
-
-            yield return new TestCaseData(
-                new TestCommand(),
-                GetCommandSchema(typeof(TestCommand)),
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("str", "hello world")
-                })
-            );
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_InitializeCommand))]
-        public void InitializeCommand_Test(ICommand command, CommandSchema commandSchema, CommandInput commandInput, ICommand expectedCommand)
-        {
-            // Arrange
-            var initializer = new CommandInitializer();
-
-            // Act
-            initializer.InitializeCommand(command, commandSchema, commandInput);
-
-            // Assert
-            command.Should().BeEquivalentTo(expectedCommand, o => o.RespectingRuntimeTypes());
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_InitializeCommand_Negative))]
-        public void InitializeCommand_Negative_Test(ICommand command, CommandSchema commandSchema, CommandInput commandInput)
-        {
-            // Arrange
-            var initializer = new CommandInitializer();
-
-            // Act & Assert
-            initializer.Invoking(i => i.InitializeCommand(command, commandSchema, commandInput))
-                .Should().ThrowExactly<MissingCommandOptionInputException>();
-        }
-    }
-}

CliFx.Tests/CommandInputParserTests.cs

@@ -1,184 +0,0 @@
-using System.Collections.Generic;
-using CliFx.Models;
-using CliFx.Services;
-using FluentAssertions;
-using NUnit.Framework;
-
-namespace CliFx.Tests
-{
-    [TestFixture]
-    public class CommandInputParserTests
-    {
-        private static IEnumerable<TestCaseData> GetTestCases_ParseCommandInput()
-        {
-            yield return new TestCaseData(new string[0], CommandInput.Empty);
-
-            yield return new TestCaseData(
-                new[] {"--option", "value"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("option", "value")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"--option1", "value1", "--option2", "value2"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("option1", "value1"),
-                    new CommandOptionInput("option2", "value2")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"--option", "value1", "value2"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("option", new[] {"value1", "value2"})
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"--option", "value1", "--option", "value2"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("option", new[] {"value1", "value2"})
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"-a", "value"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("a", "value")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"-a", "value1", "-b", "value2"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("a", "value1"),
-                    new CommandOptionInput("b", "value2")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"-a", "value1", "value2"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("a", new[] {"value1", "value2"})
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"-a", "value1", "-a", "value2"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("a", new[] {"value1", "value2"})
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"--option1", "value1", "-b", "value2"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("option1", "value1"),
-                    new CommandOptionInput("b", "value2")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"--switch"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("switch")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"--switch1", "--switch2"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("switch1"),
-                    new CommandOptionInput("switch2")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"-s"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("s")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"-a", "-b"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("a"),
-                    new CommandOptionInput("b")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"-ab"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("a"),
-                    new CommandOptionInput("b")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"-ab", "value"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("a"),
-                    new CommandOptionInput("b", "value")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"command"},
-                new CommandInput("command")
-            );
-
-            yield return new TestCaseData(
-                new[] {"command", "--option", "value"},
-                new CommandInput("command", new[]
-                {
-                    new CommandOptionInput("option", "value")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"long", "command", "name"},
-                new CommandInput("long command name")
-            );
-
-            yield return new TestCaseData(
-                new[] {"long", "command", "name", "--option", "value"},
-                new CommandInput("long command name", new[]
-                {
-                    new CommandOptionInput("option", "value")
-                })
-            );
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_ParseCommandInput))]
-        public void ParseCommandInput_Test(IReadOnlyList<string> commandLineArguments, CommandInput expectedCommandInput)
-        {
-            // Arrange
-            var parser = new CommandInputParser();
-
-            // Act
-            var commandInput = parser.ParseCommandInput(commandLineArguments);
-
-            // Assert
-            commandInput.Should().BeEquivalentTo(expectedCommandInput);
-        }
-    }
-}

CliFx.Tests/CommandOptionInputConverterTests.Types.cs

@@ -1,63 +0,0 @@
-using System;
-
-namespace CliFx.Tests
-{
-    public partial class CommandOptionInputConverterTests
-    {
-        private enum TestEnum
-        {
-            Value1,
-            Value2,
-            Value3
-        }
-
-        private class TestStringConstructable
-        {
-            public string Value { get; }
-
-            public TestStringConstructable(string value)
-            {
-                Value = value;
-            }
-        }
-
-        private class TestStringParseable
-        {
-            public string Value { get; }
-
-            private TestStringParseable(string value)
-            {
-                Value = value;
-            }
-
-            public static TestStringParseable Parse(string value) => new TestStringParseable(value);
-        }
-
-        private class TestStringParseableWithFormatProvider
-        {
-            public string Value { get; }
-
-            private TestStringParseableWithFormatProvider(string value)
-            {
-                Value = value;
-            }
-
-            public static TestStringParseableWithFormatProvider Parse(string value, IFormatProvider formatProvider) =>
-                new TestStringParseableWithFormatProvider(value + " " + formatProvider);
-        }
-    }
-
-    // Negative
-    public partial class CommandOptionInputConverterTests
-    {
-        private class NonStringParseable
-        {
-            public int Value { get; }
-
-            public NonStringParseable(int value)
-            {
-                Value = value;
-            }
-        }
-    }
-}

CliFx.Tests/CommandSchemaResolverTests.Commands.cs

@@ -1,81 +0,0 @@
-using System;
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Services;
-
-namespace CliFx.Tests
-{
-    public partial class CommandSchemaResolverTests
-    {
-        [Command("cmd", Description = "NormalCommand1 description.")]
-        private class NormalCommand1 : ICommand
-        {
-            [CommandOption("option-a", 'a')]
-            public int OptionA { get; set; }
-
-            [CommandOption("option-b", IsRequired = true)]
-            public string OptionB { get; set; }
-
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-
-        [Command(Description = "NormalCommand2 description.")]
-        private class NormalCommand2 : ICommand
-        {
-            [CommandOption("option-c", Description = "OptionC description.")]
-            public bool OptionC { get; set; }
-
-            [CommandOption("option-d", 'd')]
-            public DateTimeOffset OptionD { get; set; }
-
-            public string NotAnOption { get; set; }
-
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-    }
-
-    // Negative
-    public partial class CommandSchemaResolverTests
-    {
-        [Command("conflict")]
-        private class ConflictingCommand1 : ICommand
-        {
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-
-        [Command("conflict")]
-        private class ConflictingCommand2 : ICommand
-        {
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-
-        [Command]
-        private class InvalidCommand1
-        {
-        }
-
-        [Command]
-        private class InvalidCommand2 : ICommand
-        {
-            [CommandOption("conflict")]
-            public string ConflictingOption1 { get; set; }
-
-            [CommandOption("conflict")]
-            public string ConflictingOption2 { get; set; }
-
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-
-        [Command]
-        private class InvalidCommand3 : ICommand
-        {
-            [CommandOption('c')]
-            public string ConflictingOption1 { get; set; }
-
-            [CommandOption('c')]
-            public string ConflictingOption2 { get; set; }
-
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-    }
-}

CliFx.Tests/CommandSchemaResolverTests.cs

@@ -1,94 +0,0 @@
-using System;
-using System.Collections.Generic;
-using CliFx.Exceptions;
-using CliFx.Models;
-using CliFx.Services;
-using FluentAssertions;
-using NUnit.Framework;
-
-namespace CliFx.Tests
-{
-    [TestFixture]
-    public partial class CommandSchemaResolverTests
-    {
-        private static IEnumerable<TestCaseData> GetTestCases_GetCommandSchemas()
-        {
-            yield return new TestCaseData(
-                new[] {typeof(NormalCommand1), typeof(NormalCommand2)},
-                new[]
-                {
-                    new CommandSchema(typeof(NormalCommand1), "cmd", "NormalCommand1 description.",
-                        new[]
-                        {
-                            new CommandOptionSchema(typeof(NormalCommand1).GetProperty(nameof(NormalCommand1.OptionA)),
-                                "option-a", 'a', false, null),
-                            new CommandOptionSchema(typeof(NormalCommand1).GetProperty(nameof(NormalCommand1.OptionB)),
-                                "option-b", null, true, null)
-                        }),
-                    new CommandSchema(typeof(NormalCommand2), null, "NormalCommand2 description.",
-                        new[]
-                        {
-                            new CommandOptionSchema(typeof(NormalCommand2).GetProperty(nameof(NormalCommand2.OptionC)),
-                                "option-c", null, false, "OptionC description."),
-                            new CommandOptionSchema(typeof(NormalCommand2).GetProperty(nameof(NormalCommand2.OptionD)),
-                                "option-d", 'd', false, null)
-                        })
-                }
-            );
-        }
-
-        private static IEnumerable<TestCaseData> GetTestCases_GetCommandSchemas_Negative()
-        {
-            yield return new TestCaseData(new object[]
-            {
-                new Type[0]
-            });
-
-            yield return new TestCaseData(new object[]
-            {
-                new[] {typeof(ConflictingCommand1), typeof(ConflictingCommand2)}
-            });
-
-            yield return new TestCaseData(new object[]
-            {
-                new[] {typeof(InvalidCommand1)}
-            });
-
-            yield return new TestCaseData(new object[]
-            {
-                new[] {typeof(InvalidCommand2)}
-            });
-
-            yield return new TestCaseData(new object[]
-            {
-                new[] {typeof(InvalidCommand3)}
-            });
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_GetCommandSchemas))]
-        public void GetCommandSchemas_Test(IReadOnlyList<Type> commandTypes, IReadOnlyList<CommandSchema> expectedCommandSchemas)
-        {
-            // Arrange
-            var commandSchemaResolver = new CommandSchemaResolver();
-
-            // Act
-            var commandSchemas = commandSchemaResolver.GetCommandSchemas(commandTypes);
-
-            // Assert
-            commandSchemas.Should().BeEquivalentTo(expectedCommandSchemas);
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_GetCommandSchemas_Negative))]
-        public void GetCommandSchemas_Negative_Test(IReadOnlyList<Type> commandTypes)
-        {
-            // Arrange
-            var resolver = new CommandSchemaResolver();
-
-            // Act & Assert
-            resolver.Invoking(r => r.GetCommandSchemas(commandTypes))
-                .Should().ThrowExactly<InvalidCommandSchemaException>();
-        }
-    }
-}

CliFx.Tests/DelegateCommandFactoryTests.Commands.cs

@@ -1,15 +0,0 @@
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Services;
-
-namespace CliFx.Tests
-{
-    public partial class DelegateCommandFactoryTests
-    {
-        [Command]
-        private class TestCommand : ICommand
-        {
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-    }
-}

CliFx.Tests/DummyTests.cs

@@ -1,73 +0,0 @@
-using System.Threading.Tasks;
-using CliWrap;
-using FluentAssertions;
-using NUnit.Framework;
-
-namespace CliFx.Tests
-{
-    [TestFixture]
-    public class DummyTests
-    {
-        private static string DummyFilePath => typeof(Dummy.Program).Assembly.Location;
-
-        private static string DummyVersionText => typeof(Dummy.Program).Assembly.GetName().Version.ToString();
-
-        [Test]
-        [TestCase("", "Hello world")]
-        [TestCase("-t .NET", "Hello .NET")]
-        [TestCase("-e", "Hello world!")]
-        [TestCase("sum -v 1 2", "3")]
-        [TestCase("sum -v 2.75 3.6 4.18", "10.53")]
-        [TestCase("sum -v 4 -v 16", "20")]
-        [TestCase("sum --values 2 5 --values 3", "10")]
-        [TestCase("log -v 100", "2")]
-        [TestCase("log --value 256 --base 2", "8")]
-        public async Task CliApplication_RunAsync_Test(string arguments, string expectedOutput)
-        {
-            // Arrange & Act
-            var result = await Cli.Wrap(DummyFilePath)
-                .SetArguments(arguments)
-                .EnableExitCodeValidation()
-                .EnableStandardErrorValidation()
-                .ExecuteAsync();
-
-            // Assert
-            result.StandardOutput.Trim().Should().Be(expectedOutput);
-        }
-
-        [Test]
-        [TestCase("--version")]
-        public async Task CliApplication_RunAsync_ShowVersion_Test(string arguments)
-        {
-            // Arrange & Act
-            var result = await Cli.Wrap(DummyFilePath)
-                .SetArguments(arguments)
-                .EnableExitCodeValidation()
-                .EnableStandardErrorValidation()
-                .ExecuteAsync();
-
-            // Assert
-            result.StandardOutput.Trim().Should().Be(DummyVersionText);
-        }
-
-        [Test]
-        [TestCase("--help")]
-        [TestCase("-h")]
-        [TestCase("sum -h")]
-        [TestCase("sum --help")]
-        [TestCase("log -h")]
-        [TestCase("log --help")]
-        public async Task CliApplication_RunAsync_ShowHelp_Test(string arguments)
-        {
-            // Arrange & Act
-            var result = await Cli.Wrap(DummyFilePath)
-                .SetArguments(arguments)
-                .EnableExitCodeValidation()
-                .EnableStandardErrorValidation()
-                .ExecuteAsync();
-
-            // Assert
-            result.StandardOutput.Trim().Should().NotBeNullOrWhiteSpace();
-        }
-    }
-}

CliFx.Tests/HelpTextRendererTests.Commands.cs

@@ -1,42 +0,0 @@
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Services;
-
-namespace CliFx.Tests
-{
-    public partial class HelpTextRendererTests
-    {
-        [Command(Description = "DefaultCommand description.")]
-        private class DefaultCommand : ICommand
-        {
-            [CommandOption("option-a", 'a', Description = "OptionA description.")]
-            public string OptionA { get; set; }
-
-            [CommandOption("option-b", 'b', Description = "OptionB description.")]
-            public string OptionB { get; set; }
-
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-
-        [Command("cmd", Description = "NamedCommand description.")]
-        private class NamedCommand : ICommand
-        {
-            [CommandOption("option-c", 'c', Description = "OptionC description.")]
-            public string OptionC { get; set; }
-
-            [CommandOption("option-d", 'd', Description = "OptionD description.")]
-            public string OptionD { get; set; }
-
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-
-        [Command("cmd sub", Description = "NamedSubCommand description.")]
-        private class NamedSubCommand : ICommand
-        {
-            [CommandOption("option-e", 'e', Description = "OptionE description.")]
-            public string OptionE { get; set; }
-
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-    }
-}

CliFx.Tests/Services/CommandFactoryTests.cs

@@ -3,20 +3,21 @@ using System.Collections.Generic;
 using System.Linq;
 using CliFx.Models;
 using CliFx.Services;
+using CliFx.Tests.TestCommands;
 using FluentAssertions;
 using NUnit.Framework;
 
-namespace CliFx.Tests
+namespace CliFx.Tests.Services
 {
     [TestFixture]
-    public partial class CommandFactoryTests
+    public class CommandFactoryTests
     {
         private static CommandSchema GetCommandSchema(Type commandType) =>
             new CommandSchemaResolver().GetCommandSchemas(new[] {commandType}).Single();
 
         private static IEnumerable<TestCaseData> GetTestCases_CreateCommand()
         {
-            yield return new TestCaseData(GetCommandSchema(typeof(TestCommand)));
+            yield return new TestCaseData(GetCommandSchema(typeof(HelloWorldDefaultCommand)));
         }
 
         [Test]

CliFx.Tests/Services/CommandInitializerTests.cs

@@ -0,0 +1,173 @@
+using FluentAssertions;
+using NUnit.Framework;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using CliFx.Exceptions;
+using CliFx.Models;
+using CliFx.Services;
+using CliFx.Tests.TestCommands;
+using CliFx.Tests.Stubs;
+
+namespace CliFx.Tests.Services
+{
+    [TestFixture]
+    public class CommandInitializerTests
+    {
+        private static CommandSchema GetCommandSchema(Type commandType) =>
+            new CommandSchemaResolver().GetCommandSchemas(new[] { commandType }).Single();
+
+        private static IEnumerable<TestCaseData> GetTestCases_InitializeCommand()
+        {
+            yield return new TestCaseData(
+                new DivideCommand(),
+                GetCommandSchema(typeof(DivideCommand)),
+                new CommandInput("div", new[]
+                {
+                    new CommandOptionInput("dividend", "13"),
+                    new CommandOptionInput("divisor", "8")
+                }),
+                new DivideCommand { Dividend = 13, Divisor = 8 }
+            );
+
+            yield return new TestCaseData(
+                new DivideCommand(),
+                GetCommandSchema(typeof(DivideCommand)),
+                new CommandInput("div", new[]
+                {
+                    new CommandOptionInput("dividend", "13"),
+                    new CommandOptionInput("d", "8")
+                }),
+                new DivideCommand { Dividend = 13, Divisor = 8 }
+            );
+
+            yield return new TestCaseData(
+                new DivideCommand(),
+                GetCommandSchema(typeof(DivideCommand)),
+                new CommandInput("div", new[]
+                {
+                    new CommandOptionInput("D", "13"),
+                    new CommandOptionInput("d", "8")
+                }),
+                new DivideCommand { Dividend = 13, Divisor = 8 }
+            );
+
+            yield return new TestCaseData(
+                new ConcatCommand(),
+                GetCommandSchema(typeof(ConcatCommand)),
+                new CommandInput("concat", new[]
+                {
+                    new CommandOptionInput("i", new[] {"foo", " ", "bar"})
+                }),
+                new ConcatCommand { Inputs = new[] { "foo", " ", "bar" } }
+            );
+
+            yield return new TestCaseData(
+                new ConcatCommand(),
+                GetCommandSchema(typeof(ConcatCommand)),
+                new CommandInput("concat", new[]
+                {
+                    new CommandOptionInput("i", new[] {"foo", "bar"}),
+                    new CommandOptionInput("s", " ")
+                }),
+                new ConcatCommand { Inputs = new[] { "foo", "bar" }, Separator = " " }
+            );
+
+            //Will read a value from environment variables because none is supplied via CommandInput
+            yield return new TestCaseData(
+                new EnvironmentVariableCommand(),
+                GetCommandSchema(typeof(EnvironmentVariableCommand)),
+                new CommandInput(null, new CommandOptionInput[0], EnvironmentVariablesProviderStub.EnvironmentVariables),
+                new EnvironmentVariableCommand { Option = "A" }
+            );
+
+            //Will read multiple values from environment variables because none is supplied via CommandInput
+            yield return new TestCaseData(
+                new EnvironmentVariableWithMultipleValuesCommand(),
+                GetCommandSchema(typeof(EnvironmentVariableWithMultipleValuesCommand)),
+                new CommandInput(null, new CommandOptionInput[0], EnvironmentVariablesProviderStub.EnvironmentVariables),
+                new EnvironmentVariableWithMultipleValuesCommand { Option = new[] { "A", "B", "C" } }
+            );
+
+            //Will not read a value from environment variables because one is supplied via CommandInput
+            yield return new TestCaseData(
+                new EnvironmentVariableCommand(),
+                GetCommandSchema(typeof(EnvironmentVariableCommand)),
+                new CommandInput(null, new[]
+                {
+                    new CommandOptionInput("opt", new[] { "X" })
+                },
+                EnvironmentVariablesProviderStub.EnvironmentVariables),
+                new EnvironmentVariableCommand { Option = "X" }
+            );
+
+            //Will not split environment variable values because underlying property is not a collection
+            yield return new TestCaseData(
+                new EnvironmentVariableWithoutCollectionPropertyCommand(),
+                GetCommandSchema(typeof(EnvironmentVariableWithoutCollectionPropertyCommand)),
+                new CommandInput(null, new CommandOptionInput[0], EnvironmentVariablesProviderStub.EnvironmentVariables),
+                new EnvironmentVariableWithoutCollectionPropertyCommand { Option = "A;B;C;" }
+            );
+        }
+
+        private static IEnumerable<TestCaseData> GetTestCases_InitializeCommand_Negative()
+        {
+            yield return new TestCaseData(
+                new DivideCommand(),
+                GetCommandSchema(typeof(DivideCommand)),
+                new CommandInput("div")
+            );
+
+            yield return new TestCaseData(
+                new DivideCommand(),
+                GetCommandSchema(typeof(DivideCommand)),
+                new CommandInput("div", new[]
+                {
+                    new CommandOptionInput("D", "13")
+                })
+            );
+
+            yield return new TestCaseData(
+                new ConcatCommand(),
+                GetCommandSchema(typeof(ConcatCommand)),
+                new CommandInput("concat")
+            );
+
+            yield return new TestCaseData(
+                new ConcatCommand(),
+                GetCommandSchema(typeof(ConcatCommand)),
+                new CommandInput("concat", new[]
+                {
+                    new CommandOptionInput("s", "_")
+                })
+            );
+        }
+
+        [Test]
+        [TestCaseSource(nameof(GetTestCases_InitializeCommand))]
+        public void InitializeCommand_Test(ICommand command, CommandSchema commandSchema, CommandInput commandInput,
+            ICommand expectedCommand)
+        {
+            // Arrange
+            var initializer = new CommandInitializer();
+
+            // Act
+            initializer.InitializeCommand(command, commandSchema, commandInput);
+
+            // Assert
+            command.Should().BeEquivalentTo(expectedCommand, o => o.RespectingRuntimeTypes());
+        }
+
+        [Test]
+        [TestCaseSource(nameof(GetTestCases_InitializeCommand_Negative))]
+        public void InitializeCommand_Negative_Test(ICommand command, CommandSchema commandSchema, CommandInput commandInput)
+        {
+            // Arrange
+            var initializer = new CommandInitializer();
+
+            // Act & Assert
+            initializer.Invoking(i => i.InitializeCommand(command, commandSchema, commandInput))
+                .Should().ThrowExactly<CliFxException>();
+        }
+    }
+}

CliFx.Tests/Services/CommandInputParserTests.cs

@@ -0,0 +1,255 @@
+using FluentAssertions;
+using NUnit.Framework;
+using System.Collections.Generic;
+using CliFx.Models;
+using CliFx.Services;
+using CliFx.Tests.Stubs;
+
+namespace CliFx.Tests.Services
+{
+    [TestFixture]
+    public class CommandInputParserTests
+    {
+        private static IEnumerable<TestCaseData> GetTestCases_ParseCommandInput()
+        {
+            yield return new TestCaseData(new string[0], CommandInput.Empty, new EmptyEnvironmentVariablesProviderStub());
+
+            yield return new TestCaseData(
+                new[] { "--option", "value" },
+                new CommandInput(new[]
+                {
+                    new CommandOptionInput("option", "value")
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "--option1", "value1", "--option2", "value2" },
+                new CommandInput(new[]
+                {
+                    new CommandOptionInput("option1", "value1"),
+                    new CommandOptionInput("option2", "value2")
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "--option", "value1", "value2" },
+                new CommandInput(new[]
+                {
+                    new CommandOptionInput("option", new[] {"value1", "value2"})
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "--option", "value1", "--option", "value2" },
+                new CommandInput(new[]
+                {
+                    new CommandOptionInput("option", new[] {"value1", "value2"})
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "-a", "value" },
+                new CommandInput(new[]
+                {
+                    new CommandOptionInput("a", "value")
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "-a", "value1", "-b", "value2" },
+                new CommandInput(new[]
+                {
+                    new CommandOptionInput("a", "value1"),
+                    new CommandOptionInput("b", "value2")
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "-a", "value1", "value2" },
+                new CommandInput(new[]
+                {
+                    new CommandOptionInput("a", new[] {"value1", "value2"})
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "-a", "value1", "-a", "value2" },
+                new CommandInput(new[]
+                {
+                    new CommandOptionInput("a", new[] {"value1", "value2"})
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "--option1", "value1", "-b", "value2" },
+                new CommandInput(new[]
+                {
+                    new CommandOptionInput("option1", "value1"),
+                    new CommandOptionInput("b", "value2")
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "--switch" },
+                new CommandInput(new[]
+                {
+                    new CommandOptionInput("switch")
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "--switch1", "--switch2" },
+                new CommandInput(new[]
+                {
+                    new CommandOptionInput("switch1"),
+                    new CommandOptionInput("switch2")
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "-s" },
+                new CommandInput(new[]
+                {
+                    new CommandOptionInput("s")
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "-a", "-b" },
+                new CommandInput(new[]
+                {
+                    new CommandOptionInput("a"),
+                    new CommandOptionInput("b")
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "-ab" },
+                new CommandInput(new[]
+                {
+                    new CommandOptionInput("a"),
+                    new CommandOptionInput("b")
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "-ab", "value" },
+                new CommandInput(new[]
+                {
+                    new CommandOptionInput("a"),
+                    new CommandOptionInput("b", "value")
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "command" },
+                new CommandInput("command"),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "command", "--option", "value" },
+                new CommandInput("command", new[]
+                {
+                    new CommandOptionInput("option", "value")
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "long", "command", "name" },
+                new CommandInput("long command name"),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "long", "command", "name", "--option", "value" },
+                new CommandInput("long command name", new[]
+                {
+                    new CommandOptionInput("option", "value")
+                }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "[debug]" },
+                new CommandInput(null,
+                    new[] { "debug" },
+                    new CommandOptionInput[0]),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "[debug]", "[preview]" },
+                new CommandInput(null,
+                    new[] { "debug", "preview" },
+                    new CommandOptionInput[0]),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "[debug]", "[preview]", "-o", "value" },
+                new CommandInput(null,
+                    new[] { "debug", "preview" },
+                    new[]
+                    {
+                        new CommandOptionInput("o", "value")
+                    }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "command", "[debug]", "[preview]", "-o", "value" },
+                new CommandInput("command",
+                    new[] { "debug", "preview" },
+                    new[]
+                    {
+                        new CommandOptionInput("o", "value")
+                    }),
+                new EmptyEnvironmentVariablesProviderStub()
+            );
+
+            yield return new TestCaseData(
+                new[] { "command", "[debug]", "[preview]", "-o", "value" },
+                new CommandInput("command",
+                    new[] { "debug", "preview" },
+                    new[]
+                    {
+                        new CommandOptionInput("o", "value")
+                    },
+                    EnvironmentVariablesProviderStub.EnvironmentVariables),
+                new EnvironmentVariablesProviderStub()
+            );
+        }
+
+        [Test]
+        [TestCaseSource(nameof(GetTestCases_ParseCommandInput))]
+        public void ParseCommandInput_Test(IReadOnlyList<string> commandLineArguments,
+            CommandInput expectedCommandInput, IEnvironmentVariablesProvider environmentVariablesProvider)
+        {
+            // Arrange
+            var parser = new CommandInputParser(environmentVariablesProvider);
+
+            // Act
+            var commandInput = parser.ParseCommandInput(commandLineArguments);
+
+            // Assert
+            commandInput.Should().BeEquivalentTo(expectedCommandInput);
+        }
+    }
+}

CliFx.Tests/Services/CommandOptionInputConverterTests.cs

@@ -5,13 +5,14 @@ using System.Globalization;
 using CliFx.Exceptions;
 using CliFx.Models;
 using CliFx.Services;
+using CliFx.Tests.TestCustomTypes;
 using FluentAssertions;
 using NUnit.Framework;
 
-namespace CliFx.Tests
+namespace CliFx.Tests.Services
 {
     [TestFixture]
-    public partial class CommandOptionInputConverterTests
+    public class CommandOptionInputConverterTests
     {
         private static IEnumerable<TestCaseData> GetTestCases_ConvertOptionInput()
         {
@@ -213,6 +214,12 @@ namespace CliFx.Tests
                 new[] {47, 69}
             );
 
+            yield return new TestCaseData(
+                new CommandOptionInput("option", new[] {"47"}),
+                typeof(int[]),
+                new[] {47}
+            );
+
             yield return new TestCaseData(
                 new CommandOptionInput("option", new[] {"value1", "value3"}),
                 typeof(TestEnum[]),
@@ -269,15 +276,26 @@ namespace CliFx.Tests
                 typeof(int)
             );
 
+            yield return new TestCaseData(
+                new CommandOptionInput("option", new[] {"123", "456"}),
+                typeof(int)
+            );
+
+            yield return new TestCaseData(
+                new CommandOptionInput("option"),
+                typeof(int)
+            );
+
             yield return new TestCaseData(
                 new CommandOptionInput("option", "123"),
-                typeof(NonStringParseable)
+                typeof(TestNonStringParseable)
             );
         }
 
         [Test]
         [TestCaseSource(nameof(GetTestCases_ConvertOptionInput))]
-        public void ConvertOptionInput_Test(CommandOptionInput optionInput, Type targetType, object expectedConvertedValue)
+        public void ConvertOptionInput_Test(CommandOptionInput optionInput, Type targetType,
+            object expectedConvertedValue)
         {
             // Arrange
             var converter = new CommandOptionInputConverter();
@@ -299,7 +317,7 @@ namespace CliFx.Tests
 
             // Act & Assert
             converter.Invoking(c => c.ConvertOptionInput(optionInput, targetType))
-                .Should().ThrowExactly<InvalidCommandOptionInputException>();
+                .Should().ThrowExactly<CliFxException>();
         }
     }
 }

CliFx.Tests/Services/CommandSchemaResolverTests.cs

@@ -0,0 +1,116 @@
+using FluentAssertions;
+using NUnit.Framework;
+using System;
+using System.Collections.Generic;
+using CliFx.Exceptions;
+using CliFx.Models;
+using CliFx.Services;
+using CliFx.Tests.TestCommands;
+
+namespace CliFx.Tests.Services
+{
+    [TestFixture]
+    public class CommandSchemaResolverTests
+    {
+        private static IEnumerable<TestCaseData> GetTestCases_GetCommandSchemas()
+        {
+            yield return new TestCaseData(
+                new[] { typeof(DivideCommand), typeof(ConcatCommand), typeof(EnvironmentVariableCommand) },
+                new[]
+                {
+                    new CommandSchema(typeof(DivideCommand), "div", "Divide one number by another.",
+                        new[]
+                        {
+                            new CommandOptionSchema(typeof(DivideCommand).GetProperty(nameof(DivideCommand.Dividend)),
+                                "dividend", 'D', true, "The number to divide.", null),
+                            new CommandOptionSchema(typeof(DivideCommand).GetProperty(nameof(DivideCommand.Divisor)),
+                                "divisor", 'd', true, "The number to divide by.", null)
+                        }),
+                    new CommandSchema(typeof(ConcatCommand), "concat", "Concatenate strings.",
+                        new[]
+                        {
+                            new CommandOptionSchema(typeof(ConcatCommand).GetProperty(nameof(ConcatCommand.Inputs)),
+                                null, 'i', true, "Input strings.", null),
+                            new CommandOptionSchema(typeof(ConcatCommand).GetProperty(nameof(ConcatCommand.Separator)),
+                                null, 's', false, "String separator.", null)
+                        }),
+                    new CommandSchema(typeof(EnvironmentVariableCommand), null, "Reads option values from environment variables.",
+                        new[]
+                        {
+                            new CommandOptionSchema(typeof(EnvironmentVariableCommand).GetProperty(nameof(EnvironmentVariableCommand.Option)),
+                                "opt", null, false, null, "ENV_SINGLE_VALUE")
+                        }
+                    )
+                }
+            );
+
+            yield return new TestCaseData(
+                new[] { typeof(HelloWorldDefaultCommand) },
+                new[]
+                {
+                    new CommandSchema(typeof(HelloWorldDefaultCommand), null, null, new CommandOptionSchema[0])
+                }
+            );
+        }
+
+        private static IEnumerable<TestCaseData> GetTestCases_GetCommandSchemas_Negative()
+        {
+            yield return new TestCaseData(new object[]
+            {
+                new Type[0]
+            });
+
+            yield return new TestCaseData(new object[]
+            {
+                new[] {typeof(NonImplementedCommand)}
+            });
+
+            yield return new TestCaseData(new object[]
+            {
+                new[] {typeof(NonAnnotatedCommand)}
+            });
+
+            yield return new TestCaseData(new object[]
+            {
+                new[] {typeof(DuplicateOptionNamesCommand)}
+            });
+
+            yield return new TestCaseData(new object[]
+            {
+                new[] {typeof(DuplicateOptionShortNamesCommand)}
+            });
+
+            yield return new TestCaseData(new object[]
+            {
+                new[] {typeof(ExceptionCommand), typeof(CommandExceptionCommand)}
+            });
+        }
+
+        [Test]
+        [TestCaseSource(nameof(GetTestCases_GetCommandSchemas))]
+        public void GetCommandSchemas_Test(IReadOnlyList<Type> commandTypes,
+            IReadOnlyList<CommandSchema> expectedCommandSchemas)
+        {
+            // Arrange
+            var commandSchemaResolver = new CommandSchemaResolver();
+
+            // Act
+            var commandSchemas = commandSchemaResolver.GetCommandSchemas(commandTypes);
+
+            // Assert
+            commandSchemas.Should().BeEquivalentTo(expectedCommandSchemas);
+        }
+
+        [Test]
+        [TestCaseSource(nameof(GetTestCases_GetCommandSchemas_Negative))]
+        public void GetCommandSchemas_Negative_Test(IReadOnlyList<Type> commandTypes)
+        {
+            // Arrange
+            var resolver = new CommandSchemaResolver();
+
+            // Act & Assert
+            resolver.Invoking(r => r.GetCommandSchemas(commandTypes))
+                .Should().ThrowExactly<CliFxException>();
+        }
+    }
+}

CliFx.Tests/Services/DelegateCommandFactoryTests.cs

@@ -3,13 +3,14 @@ using System.Collections.Generic;
 using System.Linq;
 using CliFx.Models;
 using CliFx.Services;
+using CliFx.Tests.TestCommands;
 using FluentAssertions;
 using NUnit.Framework;
 
-namespace CliFx.Tests
+namespace CliFx.Tests.Services
 {
     [TestFixture]
-    public partial class DelegateCommandFactoryTests
+    public class DelegateCommandFactoryTests
     {
         private static CommandSchema GetCommandSchema(Type commandType) =>
             new CommandSchemaResolver().GetCommandSchemas(new[] {commandType}).Single();
@@ -18,7 +19,7 @@ namespace CliFx.Tests
         {
             yield return new TestCaseData(
                 new Func<CommandSchema, ICommand>(schema => (ICommand) Activator.CreateInstance(schema.Type)),
-                GetCommandSchema(typeof(TestCommand))
+                GetCommandSchema(typeof(HelloWorldDefaultCommand))
             );
         }
 

CliFx.Tests/Services/HelpTextRendererTests.cs

@@ -4,13 +4,14 @@ using System.IO;
 using System.Linq;
 using CliFx.Models;
 using CliFx.Services;
+using CliFx.Tests.TestCommands;
 using FluentAssertions;
 using NUnit.Framework;
 
-namespace CliFx.Tests
+namespace CliFx.Tests.Services
 {
     [TestFixture]
-    public partial class HelpTextRendererTests
+    public class HelpTextRendererTests
     {
         private static HelpTextSource CreateHelpTextSource(IReadOnlyList<Type> availableCommandTypes, Type targetCommandType)
         {
@@ -27,11 +28,13 @@ namespace CliFx.Tests
         {
             yield return new TestCaseData(
                 CreateHelpTextSource(
-                    new[] {typeof(DefaultCommand), typeof(NamedCommand), typeof(NamedSubCommand)},
-                    typeof(DefaultCommand)),
+                    new[] {typeof(HelpDefaultCommand), typeof(HelpNamedCommand), typeof(HelpSubCommand)},
+                    typeof(HelpDefaultCommand)),
 
                 new[]
                 {
+                    "Description",
+                    "HelpDefaultCommand description.",
                     "Usage",
                     "[command]", "[options]",
                     "Options",
@@ -40,20 +43,20 @@ namespace CliFx.Tests
                     "-h|--help", "Shows help text.",
                     "--version", "Shows version information.",
                     "Commands",
-                    "cmd", "NamedCommand description.",
+                    "cmd", "HelpNamedCommand description.",
                     "You can run", "to show help on a specific command."
                 }
             );
 
             yield return new TestCaseData(
                 CreateHelpTextSource(
-                    new[] {typeof(DefaultCommand), typeof(NamedCommand), typeof(NamedSubCommand)},
-                    typeof(NamedCommand)),
+                    new[] {typeof(HelpDefaultCommand), typeof(HelpNamedCommand), typeof(HelpSubCommand)},
+                    typeof(HelpNamedCommand)),
 
                 new[]
                 {
                     "Description",
-                    "NamedCommand description.",
+                    "HelpNamedCommand description.",
                     "Usage",
                     "cmd", "[command]", "[options]",
                     "Options",
@@ -61,20 +64,20 @@ namespace CliFx.Tests
                     "-d|--option-d", "OptionD description.",
                     "-h|--help", "Shows help text.",
                     "Commands",
-                    "sub", "NamedSubCommand description.",
+                    "sub", "HelpSubCommand description.",
                     "You can run", "to show help on a specific command."
                 }
             );
 
             yield return new TestCaseData(
                 CreateHelpTextSource(
-                    new[] {typeof(DefaultCommand), typeof(NamedCommand), typeof(NamedSubCommand)},
-                    typeof(NamedSubCommand)),
+                    new[] {typeof(HelpDefaultCommand), typeof(HelpNamedCommand), typeof(HelpSubCommand)},
+                    typeof(HelpSubCommand)),
 
                 new[]
                 {
                     "Description",
-                    "NamedSubCommand description.",
+                    "HelpSubCommand description.",
                     "Usage",
                     "cmd sub", "[options]",
                     "Options",
@@ -86,13 +89,14 @@ namespace CliFx.Tests
 
         [Test]
         [TestCaseSource(nameof(GetTestCases_RenderHelpText))]
-        public void RenderHelpText_Test(HelpTextSource source, IReadOnlyList<string> expectedSubstrings)
+        public void RenderHelpText_Test(HelpTextSource source,
+            IReadOnlyList<string> expectedSubstrings)
         {
             // Arrange
             using (var stdout = new StringWriter())
             {
-                var renderer = new HelpTextRenderer();
                 var console = new VirtualConsole(stdout);
+                var renderer = new HelpTextRenderer();
 
                 // Act
                 renderer.RenderHelpText(console, source);

CliFx.Tests/Services/SystemConsoleTests.cs

@@ -0,0 +1,41 @@
+using System;
+using CliFx.Services;
+using FluentAssertions;
+using NUnit.Framework;
+
+namespace CliFx.Tests.Services
+{
+    [TestFixture]
+    public class SystemConsoleTests
+    {
+        [TearDown]
+        public void TearDown()
+        {
+            // Reset console color so it doesn't carry on into next tests
+            Console.ResetColor();
+        }
+        
+        // Make sure console correctly wraps around System.Console
+        [Test]
+        public void All_Smoke_Test()
+        {
+            // Arrange
+            var console = new SystemConsole();
+
+            // Act
+            console.ResetColor();
+            console.ForegroundColor = ConsoleColor.DarkMagenta;
+            console.BackgroundColor = ConsoleColor.DarkMagenta;
+
+            // Assert
+            console.Input.Should().BeSameAs(Console.In);
+            console.IsInputRedirected.Should().Be(Console.IsInputRedirected);
+            console.Output.Should().BeSameAs(Console.Out);
+            console.IsOutputRedirected.Should().Be(Console.IsOutputRedirected);
+            console.Error.Should().BeSameAs(Console.Error);
+            console.IsErrorRedirected.Should().Be(Console.IsErrorRedirected);
+            console.ForegroundColor.Should().Be(Console.ForegroundColor);
+            console.BackgroundColor.Should().Be(Console.BackgroundColor);
+        }
+    }
+}

CliFx.Tests/Services/VirtualConsoleTests.cs

@@ -0,0 +1,43 @@
+using System;
+using System.IO;
+using CliFx.Services;
+using FluentAssertions;
+using NUnit.Framework;
+
+namespace CliFx.Tests.Services
+{
+    [TestFixture]
+    public class VirtualConsoleTests
+    {
+        // Make sure console uses specified streams and doesn't leak to System.Console
+        [Test]
+        public void All_Smoke_Test()
+        {
+            // Arrange
+            using (var stdin = new StringReader("hello world"))
+            using (var stdout = new StringWriter())
+            using (var stderr = new StringWriter())
+            {
+                var console = new VirtualConsole(stdin, stdout, stderr);
+
+                // Act
+                console.ResetColor();
+                console.ForegroundColor = ConsoleColor.DarkMagenta;
+                console.BackgroundColor = ConsoleColor.DarkMagenta;
+
+                // Assert
+                console.Input.Should().BeSameAs(stdin);
+                console.Input.Should().NotBeSameAs(Console.In);
+                console.IsInputRedirected.Should().BeTrue();
+                console.Output.Should().BeSameAs(stdout);
+                console.Output.Should().NotBeSameAs(Console.Out);
+                console.IsOutputRedirected.Should().BeTrue();
+                console.Error.Should().BeSameAs(stderr);
+                console.Error.Should().NotBeSameAs(Console.Error);
+                console.IsErrorRedirected.Should().BeTrue();
+                console.ForegroundColor.Should().NotBe(Console.ForegroundColor);
+                console.BackgroundColor.Should().NotBe(Console.BackgroundColor);
+            }
+        }
+    }
+}

CliFx.Tests/Stubs/EmptyEnvironmentVariablesProviderStub.cs

@@ -0,0 +1,10 @@
+using System.Collections.Generic;
+using CliFx.Services;
+
+namespace CliFx.Tests.Stubs
+{
+    public class EmptyEnvironmentVariablesProviderStub : IEnvironmentVariablesProvider
+    {
+        public IReadOnlyDictionary<string, string> GetEnvironmentVariables() => new Dictionary<string, string>();
+    }
+}

CliFx.Tests/Stubs/EnvironmentVariablesProviderStub.cs

@@ -0,0 +1,18 @@
+using System.Collections.Generic;
+using System.IO;
+using CliFx.Services;
+
+namespace CliFx.Tests.Stubs
+{
+    public class EnvironmentVariablesProviderStub : IEnvironmentVariablesProvider
+    {
+        public static readonly Dictionary<string, string> EnvironmentVariables = new Dictionary<string, string>
+        {
+            ["ENV_SINGLE_VALUE"] = "A",
+            ["ENV_MULTIPLE_VALUES"] = $"A{Path.PathSeparator}B{Path.PathSeparator}C{Path.PathSeparator}",
+            ["ENV_ESCAPED_MULTIPLE_VALUES"] = $"\"A{Path.PathSeparator}B{Path.PathSeparator}C{Path.PathSeparator}\""
+        };
+
+        public IReadOnlyDictionary<string, string> GetEnvironmentVariables() => EnvironmentVariables;
+    }
+}

CliFx.Tests/TestCommands/CancellableCommand.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Services;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("cancel")]
+    public class CancellableCommand : ICommand
+    {
+        public async Task ExecuteAsync(IConsole console)
+        {
+            await Task.Yield();
+
+            console.Output.WriteLine("Printed");
+
+            await Task.Delay(TimeSpan.FromSeconds(1), console.GetCancellationToken()).ConfigureAwait(false);
+
+            console.Output.WriteLine("Never printed");
+        }
+    }
+}

CliFx.Tests/TestCommands/CommandExceptionCommand.cs

@@ -0,0 +1,20 @@
+using System.Threading;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Exceptions;
+using CliFx.Services;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("exc")]
+    public class CommandExceptionCommand : ICommand
+    {
+        [CommandOption("code", 'c')]
+        public int ExitCode { get; set; } = 1337;
+        
+        [CommandOption("msg", 'm')]
+        public string Message { get; set; }
+        
+        public Task ExecuteAsync(IConsole console) => throw new CommandException(Message, ExitCode);
+    }
+}

CliFx.Tests/TestCommands/ConcatCommand.cs

@@ -0,0 +1,24 @@
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Services;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("concat", Description = "Concatenate strings.")]
+    public class ConcatCommand : ICommand
+    {
+        [CommandOption('i', IsRequired = true, Description = "Input strings.")]
+        public IReadOnlyList<string> Inputs { get; set; }
+
+        [CommandOption('s', Description = "String separator.")]
+        public string Separator { get; set; } = ""; 
+        
+        public Task ExecuteAsync(IConsole console)
+        {
+            console.Output.WriteLine(string.Join(Separator, Inputs));
+            return Task.CompletedTask;
+        }
+    }
+}

CliFx.Tests/TestCommands/DivideCommand.cs

@@ -0,0 +1,26 @@
+using System.Threading;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Services;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("div", Description = "Divide one number by another.")]
+    public class DivideCommand : ICommand
+    {
+        [CommandOption("dividend", 'D', IsRequired = true, Description = "The number to divide.")]
+        public double Dividend { get; set; }
+
+        [CommandOption("divisor", 'd', IsRequired = true, Description = "The number to divide by.")]
+        public double Divisor { get; set; }
+
+        // This property should be ignored by resolver
+        public bool NotAnOption { get; set; }
+        
+        public Task ExecuteAsync(IConsole console)
+        {
+            console.Output.WriteLine(Dividend / Divisor);
+            return Task.CompletedTask;
+        }
+    }
+}

CliFx.Tests/TestCommands/DuplicateOptionNamesCommand.cs

@@ -0,0 +1,19 @@
+using System.Threading;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Services;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command]
+    public class DuplicateOptionNamesCommand : ICommand
+    {
+        [CommandOption("fruits")]
+        public string Apples { get; set; }
+        
+        [CommandOption("fruits")]
+        public string Oranges { get; set; }
+        
+        public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+    }
+}

CliFx.Tests/TestCommands/DuplicateOptionShortNamesCommand.cs

@@ -0,0 +1,19 @@
+using System.Threading;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Services;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command]
+    public class DuplicateOptionShortNamesCommand : ICommand
+    {
+        [CommandOption('f')]
+        public string Apples { get; set; }
+        
+        [CommandOption('f')]
+        public string Oranges { get; set; }
+        
+        public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+    }
+}

CliFx.Tests/TestCommands/EnvironmentVariableCommand.cs

@@ -0,0 +1,16 @@
+using System.Threading;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Services;
+
+namespace CliFx.Tests.TestCommands
+{
+	[Command(Description = "Reads option values from environment variables.")]
+	public class EnvironmentVariableCommand : ICommand
+	{
+		[CommandOption("opt", EnvironmentVariableName = "ENV_SINGLE_VALUE")]
+		public string Option { get; set; }
+
+		public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+	}
+}

CliFx.Tests/TestCommands/EnvironmentVariableWithMultipleValuesCommand.cs

@@ -0,0 +1,17 @@
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Services;
+
+namespace CliFx.Tests.TestCommands
+{
+	[Command(Description = "Reads multiple option values from environment variables.")]
+	public class EnvironmentVariableWithMultipleValuesCommand : ICommand
+	{
+		[CommandOption("opt", EnvironmentVariableName = "ENV_MULTIPLE_VALUES")]
+		public IEnumerable<string> Option { get; set; }
+
+		public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+	}
+}

CliFx.Tests/TestCommands/EnvironmentVariableWithoutCollectionPropertyCommand.cs

@@ -0,0 +1,17 @@
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Services;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command(Description = "Reads one option value from environment variables because target property is not a collection.")]
+    public class EnvironmentVariableWithoutCollectionPropertyCommand : ICommand
+    {
+        [CommandOption("opt", EnvironmentVariableName = "ENV_MULTIPLE_VALUES")]
+        public string Option { get; set; }
+
+        public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+    }
+}

CliFx.Tests/TestCommands/ExceptionCommand.cs

@@ -0,0 +1,17 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Services;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("exc")]
+    public class ExceptionCommand : ICommand
+    {
+        [CommandOption("msg", 'm')]
+        public string Message { get; set; }
+        
+        public Task ExecuteAsync(IConsole console) => throw new Exception(Message);
+    }
+}

CliFx.Tests/TestCommands/HelloWorldDefaultCommand.cs

@@ -0,0 +1,17 @@
+using System.Threading;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Services;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command]
+    public class HelloWorldDefaultCommand : ICommand
+    {
+        public Task ExecuteAsync(IConsole console)
+        {
+            console.Output.WriteLine("Hello world.");
+            return Task.CompletedTask;
+        }
+    }
+}

CliFx.Tests/TestCommands/HelpDefaultCommand.cs

@@ -0,0 +1,19 @@
+using System.Threading;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Services;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command(Description = "HelpDefaultCommand description.")]
+    public class HelpDefaultCommand : ICommand
+    {
+        [CommandOption("option-a", 'a', Description = "OptionA description.")]
+        public string OptionA { get; set; }
+
+        [CommandOption("option-b", 'b', Description = "OptionB description.")]
+        public string OptionB { get; set; }
+
+        public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+    }
+}

CliFx.Tests/TestCommands/HelpNamedCommand.cs

@@ -0,0 +1,19 @@
+using System.Threading;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Services;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("cmd", Description = "HelpNamedCommand description.")]
+    public class HelpNamedCommand : ICommand
+    {
+        [CommandOption("option-c", 'c', Description = "OptionC description.")]
+        public string OptionC { get; set; }
+
+        [CommandOption("option-d", 'd', Description = "OptionD description.")]
+        public string OptionD { get; set; }
+
+        public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+    }
+}

CliFx.Tests/TestCommands/HelpSubCommand.cs

@@ -0,0 +1,16 @@
+using System.Threading;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Services;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("cmd sub", Description = "HelpSubCommand description.")]
+    public class HelpSubCommand : ICommand
+    {
+        [CommandOption("option-e", 'e', Description = "OptionE description.")]
+        public string OptionE { get; set; }
+
+        public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+    }
+}

CliFx.Tests/TestCommands/NonAnnotatedCommand.cs

@@ -0,0 +1,11 @@
+using System.Threading;
+using System.Threading.Tasks;
+using CliFx.Services;
+
+namespace CliFx.Tests.TestCommands
+{
+    public class NonAnnotatedCommand : ICommand
+    {
+        public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+    }
+}

CliFx.Tests/TestCommands/NonImplementedCommand.cs

@@ -0,0 +1,9 @@
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command]
+    public class NonImplementedCommand
+    {
+    }
+}

CliFx.Tests/TestCustomTypes/TestEnum.cs

@@ -0,0 +1,9 @@
+namespace CliFx.Tests.TestCustomTypes
+{
+    public enum TestEnum
+    {
+        Value1,
+        Value2,
+        Value3
+    }
+}

CliFx.Tests/TestCustomTypes/TestNonStringParseable.cs

@@ -0,0 +1,12 @@
+namespace CliFx.Tests.TestCustomTypes
+{
+    public class TestNonStringParseable
+    {
+        public int Value { get; }
+
+        public TestNonStringParseable(int value)
+        {
+            Value = value;
+        }
+    }
+}

CliFx.Tests/TestCustomTypes/TestStringConstructable.cs

@@ -0,0 +1,12 @@
+namespace CliFx.Tests.TestCustomTypes
+{
+    public class TestStringConstructable
+    {
+        public string Value { get; }
+
+        public TestStringConstructable(string value)
+        {
+            Value = value;
+        }
+    }
+}

CliFx.Tests/TestCustomTypes/TestStringParseable.cs

@@ -0,0 +1,14 @@
+namespace CliFx.Tests.TestCustomTypes
+{
+    public class TestStringParseable
+    {
+        public string Value { get; }
+
+        private TestStringParseable(string value)
+        {
+            Value = value;
+        }
+
+        public static TestStringParseable Parse(string value) => new TestStringParseable(value);
+    }
+}

CliFx.Tests/TestCustomTypes/TestStringParseableWithFormatProvider.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace CliFx.Tests.TestCustomTypes
+{
+    public class TestStringParseableWithFormatProvider
+    {
+        public string Value { get; }
+
+        private TestStringParseableWithFormatProvider(string value)
+        {
+            Value = value;
+        }
+
+        public static TestStringParseableWithFormatProvider Parse(string value, IFormatProvider formatProvider) =>
+            new TestStringParseableWithFormatProvider(value + " " + formatProvider);
+    }
+}

CliFx.Tests/Utilities/ProgressTickerTests.cs

@@ -0,0 +1,57 @@
+using System.Globalization;
+using System.IO;
+using System.Linq;
+using CliFx.Services;
+using CliFx.Utilities;
+using FluentAssertions;
+using NUnit.Framework;
+
+namespace CliFx.Tests.Utilities
+{
+    [TestFixture]
+    public class ProgressTickerTests
+    {
+        [Test]
+        public void Report_Test()
+        {
+            // Arrange
+            var formatProvider = CultureInfo.InvariantCulture;
+
+            using (var stdout = new StringWriter(formatProvider))
+            {
+                var console = new VirtualConsole(TextReader.Null, false, stdout, false, TextWriter.Null, false);
+                var ticker = console.CreateProgressTicker();
+
+                var progressValues = Enumerable.Range(0, 100).Select(p => p / 100.0).ToArray();
+                var progressStringValues = progressValues.Select(p => p.ToString("P2", formatProvider)).ToArray();
+
+                // Act
+                foreach (var progress in progressValues)
+                    ticker.Report(progress);
+
+                // Assert
+                stdout.ToString().Should().ContainAll(progressStringValues);
+            }
+        }
+
+        [Test]
+        public void Report_Redirected_Test()
+        {
+            // Arrange
+            using (var stdout = new StringWriter())
+            {
+                var console = new VirtualConsole(stdout);
+                var ticker = console.CreateProgressTicker();
+
+                var progressValues = Enumerable.Range(0, 100).Select(p => p / 100.0).ToArray();
+
+                // Act
+                foreach (var progress in progressValues)
+                    ticker.Report(progress);
+
+                // Assert
+                stdout.ToString().Should().BeEmpty();
+            }
+        }
+    }
+}

CliFx.sln

@@ -7,8 +7,6 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx", "CliFx\CliFx.csproj
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx.Tests", "CliFx.Tests\CliFx.Tests.csproj", "{268CF863-65A5-49BB-93CF-08972B7756DC}"
 EndProject
-Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx.Tests.Dummy", "CliFx.Tests.Dummy\CliFx.Tests.Dummy.csproj", "{4904B3EB-3286-4F1B-8B74-6FF051C8E787}"
-EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{3AAE8166-BB8E-49DA-844C-3A0EE6BD40A0}"
 	ProjectSection(SolutionItems) = preProject
 		Changelog.md = Changelog.md
@@ -18,7 +16,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx.Benchmarks", "CliFx.Benchmarks\CliFx.Benchmarks.csproj", "{8ACD6DC2-D768-4850-9223-5B7C83A78513}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "CliFx.Demo", "CliFx.Demo\CliFx.Demo.csproj", "{AAB6844C-BF71-448F-A11B-89AEE459AB15}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx.Demo", "CliFx.Demo\CliFx.Demo.csproj", "{AAB6844C-BF71-448F-A11B-89AEE459AB15}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
@@ -54,18 +52,6 @@ Global
 		{268CF863-65A5-49BB-93CF-08972B7756DC}.Release|x64.Build.0 = Release|Any CPU
 		{268CF863-65A5-49BB-93CF-08972B7756DC}.Release|x86.ActiveCfg = Release|Any CPU
 		{268CF863-65A5-49BB-93CF-08972B7756DC}.Release|x86.Build.0 = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|x64.ActiveCfg = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|x64.Build.0 = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|x86.ActiveCfg = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|x86.Build.0 = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|Any CPU.Build.0 = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|x64.ActiveCfg = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|x64.Build.0 = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|x86.ActiveCfg = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|x86.Build.0 = Release|Any CPU
 		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Debug|x64.ActiveCfg = Debug|Any CPU

CliFx/Attributes/CommandOptionAttribute.cs

@@ -28,6 +28,11 @@ namespace CliFx.Attributes
         /// </summary>
         public string Description { get; set; }
 
+        /// <summary>
+        /// Optional environment variable name that will be used as fallback value if no option value is specified.
+        /// </summary>
+        public string EnvironmentVariableName { get; set; }
+
         /// <summary>
         /// Initializes an instance of <see cref="CommandOptionAttribute"/>.
         /// </summary>
@@ -41,7 +46,7 @@ namespace CliFx.Attributes
         /// Initializes an instance of <see cref="CommandOptionAttribute"/>.
         /// </summary>
         public CommandOptionAttribute(string name, char shortName)
-            : this(name, (char?) shortName)
+            : this(name, (char?)shortName)
         {
         }
 

CliFx/CliApplication.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Threading.Tasks;
 using CliFx.Exceptions;
@@ -42,6 +43,140 @@ namespace CliFx
             _helpTextRenderer = helpTextRenderer.GuardNotNull(nameof(helpTextRenderer));
         }
 
+        private async Task<int?> HandleDebugDirectiveAsync(CommandInput commandInput)
+        {
+            // Debug mode is enabled if it's allowed in the application and it was requested via corresponding directive
+            var isDebugMode = _configuration.IsDebugModeAllowed && commandInput.IsDebugDirectiveSpecified();
+
+            // If not in debug mode, pass execution to the next handler
+            if (!isDebugMode)
+                return null;
+
+            // Inform user which process they need to attach debugger to
+            _console.WithForegroundColor(ConsoleColor.Green,
+                () => _console.Output.WriteLine($"Attach debugger to PID {Process.GetCurrentProcess().Id} to continue."));
+
+            // Wait until debugger is attached
+            while (!Debugger.IsAttached)
+                await Task.Delay(100);
+
+            // Debug directive never short-circuits
+            return null;
+        }
+
+        private int? HandlePreviewDirective(CommandInput commandInput)
+        {
+            // Preview mode is enabled if it's allowed in the application and it was requested via corresponding directive
+            var isPreviewMode = _configuration.IsPreviewModeAllowed && commandInput.IsPreviewDirectiveSpecified();
+
+            // If not in preview mode, pass execution to the next handler
+            if (!isPreviewMode)
+                return null;
+
+            // Render command name
+            _console.Output.WriteLine($"Command name: {commandInput.CommandName}");
+            _console.Output.WriteLine();
+
+            // Render directives
+            _console.Output.WriteLine("Directives:");
+            foreach (var directive in commandInput.Directives)
+            {
+                _console.Output.Write(" ");
+                _console.Output.WriteLine(directive);
+            }
+
+            // Margin
+            _console.Output.WriteLine();
+
+            // Render options
+            _console.Output.WriteLine("Options:");
+            foreach (var option in commandInput.Options)
+            {
+                _console.Output.Write(" ");
+                _console.Output.WriteLine(option);
+            }
+
+            // Short-circuit with exit code 0
+            return 0;
+        }
+
+        private int? HandleVersionOption(CommandInput commandInput)
+        {
+            // Version should be rendered if it was requested on a default command
+            var shouldRenderVersion = !commandInput.IsCommandSpecified() && commandInput.IsVersionOptionSpecified();
+
+            // If shouldn't render version, pass execution to the next handler
+            if (!shouldRenderVersion)
+                return null;
+
+            // Render version text
+            _console.Output.WriteLine(_metadata.VersionText);
+
+            // Short-circuit with exit code 0
+            return 0;
+        }
+
+        private int? HandleHelpOption(CommandInput commandInput,
+            IReadOnlyList<CommandSchema> availableCommandSchemas, CommandSchema targetCommandSchema)
+        {
+            // Help should be rendered if it was requested, or when executing a command which isn't defined
+            var shouldRenderHelp = commandInput.IsHelpOptionSpecified() || targetCommandSchema == null;
+
+            // If shouldn't render help, pass execution to the next handler
+            if (!shouldRenderHelp)
+                return null;
+
+            // Keep track whether there was an error in the input
+            var isError = false;
+
+            // If target command isn't defined, find its contextual replacement
+            if (targetCommandSchema == null)
+            {
+                // If command was specified, inform the user that it's not defined
+                if (commandInput.IsCommandSpecified())
+                {
+                    _console.WithForegroundColor(ConsoleColor.Red,
+                        () => _console.Error.WriteLine($"Specified command [{commandInput.CommandName}] is not defined."));
+
+                    isError = true;
+                }
+
+                // Replace target command with closest parent of specified command
+                targetCommandSchema = availableCommandSchemas.FindParent(commandInput.CommandName);
+
+                // If there's no parent, replace with stub default command
+                if (targetCommandSchema == null)
+                {
+                    targetCommandSchema = CommandSchema.StubDefaultCommand;
+                    availableCommandSchemas = availableCommandSchemas.Concat(CommandSchema.StubDefaultCommand).ToArray();
+                }
+            }
+
+            // Build help text source
+            var helpTextSource = new HelpTextSource(_metadata, availableCommandSchemas, targetCommandSchema);
+
+            // Render help text
+            _helpTextRenderer.RenderHelpText(_console, helpTextSource);
+
+            // Short-circuit with appropriate exit code
+            return isError ? -1 : 0;
+        }
+
+        private async Task<int> HandleCommandExecutionAsync(CommandInput commandInput, CommandSchema targetCommandSchema)
+        {
+            // Create an instance of the command
+            var command = _commandFactory.CreateCommand(targetCommandSchema);
+
+            // Populate command with options according to its schema
+            _commandInitializer.InitializeCommand(command, targetCommandSchema, commandInput);
+
+            // Execute command
+            await command.ExecuteAsync(_console);
+
+            // Finish the chain with exit code 0
+            return 0;
+        }
+
         /// <inheritdoc />
         public async Task<int> RunAsync(IReadOnlyList<string> commandLineArguments)
         {
@@ -49,95 +184,47 @@ namespace CliFx
 
             try
             {
-                // Get schemas for all available command types
-                var availableCommandSchemas = _commandSchemaResolver.GetCommandSchemas(_configuration.CommandTypes);
-
                 // Parse command input from arguments
                 var commandInput = _commandInputParser.ParseCommandInput(commandLineArguments);
 
+                // Get schemas for all available command types
+                var availableCommandSchemas = _commandSchemaResolver.GetCommandSchemas(_configuration.CommandTypes);
+
                 // Find command schema matching the name specified in the input
                 var targetCommandSchema = availableCommandSchemas.FindByName(commandInput.CommandName);
 
-                // Handle cases where requested command is not defined
-                if (targetCommandSchema == null)
-                {
-                    var isError = false;
-
-                    // If specified a command - show error
-                    if (commandInput.IsCommandSpecified())
-                    {
-                        isError = true;
-
-                        _console.WithForegroundColor(ConsoleColor.Red,
-                            () => _console.Error.WriteLine($"Specified command [{commandInput.CommandName}] is not defined."));
-                    }
-
-                    // Get parent command schema
-                    var parentCommandSchema = availableCommandSchemas.FindParent(commandInput.CommandName);
-
-                    // Show help for parent command if it's defined
-                    if (parentCommandSchema != null)
-                    {
-                        var helpTextSource = new HelpTextSource(_metadata, availableCommandSchemas, parentCommandSchema);
-                        _helpTextRenderer.RenderHelpText(_console, helpTextSource);
-                    }
-                    // Otherwise show help for a stub default command
-                    else
-                    {
-                        var helpTextSource = new HelpTextSource(_metadata,
-                            availableCommandSchemas.Concat(CommandSchema.StubDefaultCommand).ToArray(),
-                            CommandSchema.StubDefaultCommand);
-
-                        _helpTextRenderer.RenderHelpText(_console, helpTextSource);
-                    }
-
-                    return isError ? -1 : 0;
-                }
-
-                // Show version if it was requested without specifying a command
-                if (commandInput.IsVersionRequested() && !commandInput.IsCommandSpecified())
-                {
-                    _console.Output.WriteLine(_metadata.VersionText);
-
-                    return 0;
-                }
-
-                // Show help if it was requested
-                if (commandInput.IsHelpRequested())
-                {
-                    var helpTextSource = new HelpTextSource(_metadata, availableCommandSchemas, targetCommandSchema);
-                    _helpTextRenderer.RenderHelpText(_console, helpTextSource);
-
-                    return 0;
-                }
-
-                // Create an instance of the command
-                var command = _commandFactory.CreateCommand(targetCommandSchema);
-
-                // Populate command with options according to its schema
-                _commandInitializer.InitializeCommand(command, targetCommandSchema, commandInput);
-
-                // Execute command
-                await command.ExecuteAsync(_console);
-
-                return 0;
+                // Chain handlers until the first one that produces an exit code
+                return
+                    await HandleDebugDirectiveAsync(commandInput) ??
+                    HandlePreviewDirective(commandInput) ??
+                    HandleVersionOption(commandInput) ??
+                    HandleHelpOption(commandInput, availableCommandSchemas, targetCommandSchema) ??
+                    await HandleCommandExecutionAsync(commandInput, targetCommandSchema);
             }
             catch (Exception ex)
             {
                 // We want to catch exceptions in order to print errors and return correct exit codes.
-                // Also, by doing this we get rid of the annoying Windows troubleshooting dialog that shows up on unhandled exceptions.
+                // Doing this also gets rid of the annoying Windows troubleshooting dialog that shows up on unhandled exceptions.
 
-                // In case we catch a CliFx-specific exception, we want to just show the error message, not the stack trace.
-                // Stack trace isn't very useful to the user if the exception is not really coming from their code.
+                // Prefer showing message without stack trace on exceptions coming from CliFx or on CommandException
+                if (!ex.Message.IsNullOrWhiteSpace() && (ex is CliFxException || ex is CommandException))
+                {
+                    _console.WithForegroundColor(ConsoleColor.Red, () => _console.Error.WriteLine(ex.Message));
+                }
+                else
+                {
+                    _console.WithForegroundColor(ConsoleColor.Red, () => _console.Error.WriteLine(ex));
+                }
 
-                // CommandException is the same, but it also lets users specify exit code so we want to return that instead of default.
-
-                var message = ex is CliFxException && !ex.Message.IsNullOrWhiteSpace() ? ex.Message : ex.ToString();
-                var exitCode = ex is CommandException commandEx ? commandEx.ExitCode : ex.HResult;
-
-                _console.WithForegroundColor(ConsoleColor.Red, () => _console.Error.WriteLine(message));
-
-                return exitCode;
+                // Return exit code if it was specified via CommandException
+                if (ex is CommandException commandException)
+                {
+                    return commandException.ExitCode;
+                }
+                else
+                {
+                    return ex.HResult;
+                }
             }
         }
     }

CliFx/CliApplicationBuilder.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using System.Reflection;
+using CliFx.Attributes;
 using CliFx.Internal;
 using CliFx.Models;
 using CliFx.Services;
@@ -16,12 +17,16 @@ namespace CliFx
     {
         private readonly HashSet<Type> _commandTypes = new HashSet<Type>();
 
+        private bool _isDebugModeAllowed = true;
+        private bool _isPreviewModeAllowed = true;
         private string _title;
         private string _executableName;
         private string _versionText;
         private string _description;
         private IConsole _console;
         private ICommandFactory _commandFactory;
+        private ICommandOptionInputConverter _commandOptionInputConverter;
+        private IEnvironmentVariablesProvider _environmentVariablesProvider;
 
         /// <inheritdoc />
         public ICliApplicationBuilder AddCommand(Type commandType)
@@ -38,7 +43,10 @@ namespace CliFx
         {
             commandAssembly.GuardNotNull(nameof(commandAssembly));
 
-            var commandTypes = commandAssembly.ExportedTypes.Where(t => t.Implements(typeof(ICommand)));
+            var commandTypes = commandAssembly.ExportedTypes
+                .Where(t => t.Implements(typeof(ICommand)))
+                .Where(t => t.IsDefined(typeof(CommandAttribute)))
+                .Where(t => !t.IsAbstract && !t.IsInterface);
 
             foreach (var commandType in commandTypes)
                 AddCommand(commandType);
@@ -46,6 +54,20 @@ namespace CliFx
             return this;
         }
 
+        /// <inheritdoc />
+        public ICliApplicationBuilder AllowDebugMode(bool isAllowed = true)
+        {
+            _isDebugModeAllowed = isAllowed;
+            return this;
+        }
+
+        /// <inheritdoc />
+        public ICliApplicationBuilder AllowPreviewMode(bool isAllowed = true)
+        {
+            _isPreviewModeAllowed = isAllowed;
+            return this;
+        }
+
         /// <inheritdoc />
         public ICliApplicationBuilder UseTitle(string title)
         {
@@ -88,70 +110,39 @@ namespace CliFx
             return this;
         }
 
-        private void SetFallbackValues()
+        /// <inheritdoc />
+        public ICliApplicationBuilder UseCommandOptionInputConverter(ICommandOptionInputConverter converter)
         {
-            if (_title.IsNullOrWhiteSpace())
-            {
-                // Entry assembly is null in tests
-                UseTitle(EntryAssembly?.GetName().Name ?? "App");
-            }
+            _commandOptionInputConverter = converter.GuardNotNull(nameof(converter));
+            return this;
+        }
 
-            if (_executableName.IsNullOrWhiteSpace())
-            {
-                // Entry assembly is null in tests
-                var entryAssemblyLocation = EntryAssembly?.Location;
-
-                // Set different executable name depending on location
-                if (!entryAssemblyLocation.IsNullOrWhiteSpace())
-                {
-                    // Prepend 'dotnet' to assembly file name if the entry assembly is a dll file (extension needs to be kept)
-                    if (string.Equals(Path.GetExtension(entryAssemblyLocation), ".dll", StringComparison.OrdinalIgnoreCase))
-                    {
-                        UseExecutableName("dotnet " + Path.GetFileName(entryAssemblyLocation));
-                    }
-                    // Otherwise just use assembly file name without extension
-                    else
-                    {
-                        UseExecutableName(Path.GetFileNameWithoutExtension(entryAssemblyLocation));
-                    }
-                }
-                // If location is null then just use a stub
-                else
-                {
-                    UseExecutableName("app");
-                }
-            }
-
-            if (_versionText.IsNullOrWhiteSpace())
-            {
-                // Entry assembly is null in tests
-                UseVersionText(EntryAssembly?.GetName().Version.ToString() ?? "1.0");
-            }
-
-            if (_console == null)
-            {
-                UseConsole(new SystemConsole());
-            }
-
-            if (_commandFactory == null)
-            {
-                UseCommandFactory(new CommandFactory());
-            }
+        /// <inheritdoc />
+        public ICliApplicationBuilder UseEnvironmentVariablesProvider(IEnvironmentVariablesProvider environmentVariablesProvider)
+        {
+            _environmentVariablesProvider = environmentVariablesProvider.GuardNotNull(nameof(environmentVariablesProvider));
+            return this;
         }
 
         /// <inheritdoc />
         public ICliApplication Build()
         {
             // Use defaults for required parameters that were not configured
-            SetFallbackValues();
+            _title = _title ?? GetDefaultTitle() ?? "App";
+            _executableName = _executableName ?? GetDefaultExecutableName() ?? "app";
+            _versionText = _versionText ?? GetDefaultVersionText() ?? "v1.0";
+            _console = _console ?? new SystemConsole();
+            _commandFactory = _commandFactory ?? new CommandFactory();
+            _commandOptionInputConverter = _commandOptionInputConverter ?? new CommandOptionInputConverter();
+            _environmentVariablesProvider = _environmentVariablesProvider ?? new EnvironmentVariablesProvider();
 
             // Project parameters to expected types
             var metadata = new ApplicationMetadata(_title, _executableName, _versionText, _description);
-            var configuration = new ApplicationConfiguration(_commandTypes.ToArray());
+            var configuration = new ApplicationConfiguration(_commandTypes.ToArray(), _isDebugModeAllowed, _isPreviewModeAllowed);
 
             return new CliApplication(metadata, configuration,
-                _console, new CommandInputParser(), new CommandSchemaResolver(),
-                _commandFactory, new CommandInitializer(), new HelpTextRenderer());
+                _console, new CommandInputParser(_environmentVariablesProvider), new CommandSchemaResolver(),
+                _commandFactory, new CommandInitializer(_commandOptionInputConverter, new EnvironmentVariablesParser()), new HelpTextRenderer());
         }
     }
 
@@ -159,6 +150,25 @@ namespace CliFx
     {
         private static readonly Lazy<Assembly> LazyEntryAssembly = new Lazy<Assembly>(Assembly.GetEntryAssembly);
 
+        // Entry assembly is null in tests
         private static Assembly EntryAssembly => LazyEntryAssembly.Value;
+
+        private static string GetDefaultTitle() => EntryAssembly?.GetName().Name;
+
+        private static string GetDefaultExecutableName()
+        {
+            var entryAssemblyLocation = EntryAssembly?.Location;
+
+            // If it's a .dll assembly, prepend 'dotnet' and keep the file extension
+            if (string.Equals(Path.GetExtension(entryAssemblyLocation), ".dll", StringComparison.OrdinalIgnoreCase))
+            {
+                return "dotnet " + Path.GetFileName(entryAssemblyLocation);
+            }
+
+            // Otherwise just use assembly file name without extension
+            return Path.GetFileNameWithoutExtension(entryAssemblyLocation);
+        }
+
+        private static string GetDefaultVersionText() => EntryAssembly != null ? $"v{EntryAssembly.GetName().Version}" : null;
     }
 }

CliFx/CliFx.csproj

@@ -2,8 +2,7 @@
 
   <PropertyGroup>
     <TargetFrameworks>net45;netstandard2.0</TargetFrameworks>
-    <LangVersion>latest</LangVersion>
-    <Version>0.0.2</Version>
+    <Version>0.0.7</Version>
     <Company>Tyrrrz</Company>
     <Authors>$(Company)</Authors>
     <Copyright>Copyright (C) Alexey Golub</Copyright>
@@ -11,7 +10,7 @@
     <PackageTags>command line executable interface framework parser arguments net core</PackageTags>
     <PackageProjectUrl>https://github.com/Tyrrrz/CliFx</PackageProjectUrl>
     <PackageReleaseNotes>https://github.com/Tyrrrz/CliFx/blob/master/Changelog.md</PackageReleaseNotes>
-    <PackageIconUrl>https://raw.githubusercontent.com/Tyrrrz/CliFx/master/favicon.png</PackageIconUrl>
+    <PackageIcon>favicon.png</PackageIcon>
     <PackageLicenseExpression>LGPL-3.0-only</PackageLicenseExpression>
     <RepositoryUrl>https://github.com/Tyrrrz/CliFx</RepositoryUrl>
     <RepositoryType>git</RepositoryType>
@@ -20,4 +19,8 @@
     <DocumentationFile>bin/$(Configuration)/$(TargetFramework)/$(AssemblyName).xml</DocumentationFile>
   </PropertyGroup>
 
-</Project>
+  <ItemGroup>
+    <None Include="../favicon.png" Pack="True" PackagePath="" />
+  </ItemGroup>
+
+</Project>

CliFx/Exceptions/CliFxException.cs

@@ -5,12 +5,12 @@ namespace CliFx.Exceptions
     /// <summary>
     /// Domain exception thrown within CliFx.
     /// </summary>
-    public abstract class CliFxException : Exception
+    public class CliFxException : Exception
     {
         /// <summary>
         /// Initializes an instance of <see cref="CliFxException"/>.
         /// </summary>
-        protected CliFxException(string message)
+        public CliFxException(string message)
             : base(message)
         {
         }
@@ -18,7 +18,7 @@ namespace CliFx.Exceptions
         /// <summary>
         /// Initializes an instance of <see cref="CliFxException"/>.
         /// </summary>
-        protected CliFxException(string message, Exception innerException)
+        public CliFxException(string message, Exception innerException)
             : base(message, innerException)
         {
         }

CliFx/Exceptions/CommandException.cs

@@ -8,7 +8,7 @@ namespace CliFx.Exceptions
     /// Use this exception if you want to report an error that occured during execution of a command.
     /// This exception also allows specifying exit code which will be returned to the calling process.
     /// </summary>
-    public class CommandException : CliFxException
+    public class CommandException : Exception
     {
         private const int DefaultExitCode = -100;
 

CliFx/Exceptions/InvalidCommandOptionInputException.cs

@@ -1,26 +0,0 @@
-using System;
-
-namespace CliFx.Exceptions
-{
-    /// <summary>
-    /// Thrown when a command option can't be converted to target type specified in its schema.
-    /// </summary>
-    public class InvalidCommandOptionInputException : CliFxException
-    {
-        /// <summary>
-        /// Initializes an instance of <see cref="InvalidCommandOptionInputException"/>.
-        /// </summary>
-        public InvalidCommandOptionInputException(string message)
-            : base(message)
-        {
-        }
-
-        /// <summary>
-        /// Initializes an instance of <see cref="InvalidCommandOptionInputException"/>.
-        /// </summary>
-        public InvalidCommandOptionInputException(string message, Exception innerException)
-            : base(message, innerException)
-        {
-        }
-    }
-}

CliFx/Exceptions/InvalidCommandSchemaException.cs

@@ -1,26 +0,0 @@
-using System;
-
-namespace CliFx.Exceptions
-{
-    /// <summary>
-    /// Thrown when a command schema fails validation.
-    /// </summary>
-    public class InvalidCommandSchemaException : CliFxException
-    {
-        /// <summary>
-        /// Initializes an instance of <see cref="InvalidCommandSchemaException"/>.
-        /// </summary>
-        public InvalidCommandSchemaException(string message)
-            : base(message)
-        {
-        }
-
-        /// <summary>
-        /// Initializes an instance of <see cref="InvalidCommandSchemaException"/>.
-        /// </summary>
-        public InvalidCommandSchemaException(string message, Exception innerException)
-            : base(message, innerException)
-        {
-        }
-    }
-}

CliFx/Exceptions/MissingCommandOptionInputException.cs

@@ -1,26 +0,0 @@
-using System;
-
-namespace CliFx.Exceptions
-{
-    /// <summary>
-    /// Thrown when a required command option was not set.
-    /// </summary>
-    public class MissingCommandOptionInputException : CliFxException
-    {
-        /// <summary>
-        /// Initializes an instance of <see cref="MissingCommandOptionInputException"/>.
-        /// </summary>
-        public MissingCommandOptionInputException(string message)
-            : base(message)
-        {
-        }
-
-        /// <summary>
-        /// Initializes an instance of <see cref="MissingCommandOptionInputException"/>.
-        /// </summary>
-        public MissingCommandOptionInputException(string message, Exception innerException)
-            : base(message, innerException)
-        {
-        }
-    }
-}

CliFx/ICliApplicationBuilder.cs

@@ -19,6 +19,16 @@ namespace CliFx
         /// </summary>
         ICliApplicationBuilder AddCommandsFrom(Assembly commandAssembly);
 
+        /// <summary>
+        /// Specifies whether debug mode (enabled with [debug] directive) is allowed in the application.
+        /// </summary>
+        ICliApplicationBuilder AllowDebugMode(bool isAllowed = true);
+
+        /// <summary>
+        /// Specifies whether preview mode (enabled with [preview] directive) is allowed in the application.
+        /// </summary>
+        ICliApplicationBuilder AllowPreviewMode(bool isAllowed = true);
+
         /// <summary>
         /// Sets application title, which appears in the help text.
         /// </summary>
@@ -49,6 +59,16 @@ namespace CliFx
         /// </summary>
         ICliApplicationBuilder UseCommandFactory(ICommandFactory factory);
 
+        /// <summary>
+        /// Configures application to use specified implementation of <see cref="ICommandOptionInputConverter"/>.
+        /// </summary>
+        ICliApplicationBuilder UseCommandOptionInputConverter(ICommandOptionInputConverter converter);
+
+        /// <summary>
+        /// Configures application to use specified implementation of <see cref="IEnvironmentVariablesProvider"/>.
+        /// </summary>
+        ICliApplicationBuilder UseEnvironmentVariablesProvider(IEnvironmentVariablesProvider environmentVariablesProvider);
+
         /// <summary>
         /// Creates an instance of <see cref="ICliApplication"/> using configured parameters.
         /// Default values are used in place of parameters that were not specified.

CliFx/ICommand.cs

@@ -1,4 +1,5 @@
-using System.Threading.Tasks;
+using System.Threading;
+using System.Threading.Tasks;
 using CliFx.Services;
 
 namespace CliFx

CliFx/Internal/Extensions.cs

@@ -26,11 +26,6 @@ namespace CliFx.Internal
         public static StringBuilder AppendIfNotEmpty(this StringBuilder builder, char value) =>
             builder.Length > 0 ? builder.Append(value) : builder;
 
-        public static TValue GetValueOrDefault<TKey, TValue>(this IReadOnlyDictionary<TKey, TValue> dic, TKey key) =>
-            dic.TryGetValue(key, out var result) ? result : default;
-
-        public static IEnumerable<T> ExceptNull<T>(this IEnumerable<T> source) where T : class => source.Where(i => i != null);
-
         public static IEnumerable<T> Concat<T>(this IEnumerable<T> source, T value)
         {
             foreach (var i in source)
@@ -41,8 +36,13 @@ namespace CliFx.Internal
 
         public static bool Implements(this Type type, Type interfaceType) => type.GetInterfaces().Contains(interfaceType);
 
+        public static Type GetNullableUnderlyingType(this Type type) => Nullable.GetUnderlyingType(type);
+
         public static Type GetEnumerableUnderlyingType(this Type type)
         {
+            if (type.IsPrimitive)
+                return null;
+
             if (type == typeof(IEnumerable))
                 return typeof(object);
 
@@ -51,7 +51,7 @@ namespace CliFx.Internal
 
             return type.GetInterfaces()
                 .Select(GetEnumerableUnderlyingType)
-                .ExceptNull()
+                .Where(t => t != default)
                 .OrderByDescending(t => t != typeof(object)) // prioritize more specific types
                 .FirstOrDefault();
         }

CliFx/Models/ApplicationConfiguration.cs

@@ -10,16 +10,29 @@ namespace CliFx.Models
     public class ApplicationConfiguration
     {
         /// <summary>
-        /// Command types defined in the application.
+        /// Command types defined in this application.
         /// </summary>
         public IReadOnlyList<Type> CommandTypes { get; }
 
+        /// <summary>
+        /// Whether debug mode is allowed in this application.
+        /// </summary>
+        public bool IsDebugModeAllowed { get; }
+
+        /// <summary>
+        /// Whether preview mode is allowed in this application.
+        /// </summary>
+        public bool IsPreviewModeAllowed { get; }
+
         /// <summary>
         /// Initializes an instance of <see cref="ApplicationConfiguration"/>.
         /// </summary>
-        public ApplicationConfiguration(IReadOnlyList<Type> commandTypes)
+        public ApplicationConfiguration(IReadOnlyList<Type> commandTypes,
+            bool isDebugModeAllowed, bool isPreviewModeAllowed)
         {
             CommandTypes = commandTypes.GuardNotNull(nameof(commandTypes));
+            IsDebugModeAllowed = isDebugModeAllowed;
+            IsPreviewModeAllowed = isPreviewModeAllowed;
         }
     }
 }

CliFx/Models/CommandInput.cs

@@ -15,18 +15,54 @@ namespace CliFx.Models
         /// </summary>
         public string CommandName { get; }
 
+        /// <summary>
+        /// Specified directives.
+        /// </summary>
+        public IReadOnlyList<string> Directives { get; }
+
         /// <summary>
         /// Specified options.
         /// </summary>
         public IReadOnlyList<CommandOptionInput> Options { get; }
 
+        /// <summary>
+        /// Environment variables available when the command was parsed
+        /// </summary>
+        public IReadOnlyDictionary<string, string> EnvironmentVariables { get; }
+
+        /// <summary>
+        /// Initializes an instance of <see cref="CommandInput"/>.
+        /// </summary>
+        public CommandInput(string commandName, IReadOnlyList<string> directives, IReadOnlyList<CommandOptionInput> options, IReadOnlyDictionary<string, string> environmentVariables)
+        {
+            CommandName = commandName; // can be null
+            Directives = directives.GuardNotNull(nameof(directives));
+            Options = options.GuardNotNull(nameof(options));
+            EnvironmentVariables = environmentVariables.GuardNotNull(nameof(environmentVariables));
+        }
+
+        /// <summary>
+        /// Initializes an instance of <see cref="CommandInput"/>.
+        /// </summary>
+        public CommandInput(string commandName, IReadOnlyList<string> directives, IReadOnlyList<CommandOptionInput> options)
+            : this(commandName, directives, options, EmptyEnvironmentVariables)
+        {
+        }
+
+        /// <summary>
+        /// Initializes an instance of <see cref="CommandInput"/>.
+        /// </summary>
+        public CommandInput(string commandName, IReadOnlyList<CommandOptionInput> options, IReadOnlyDictionary<string, string> environmentVariables)
+            : this(commandName, EmptyDirectives, options, environmentVariables)
+        {
+        }
+
         /// <summary>
         /// Initializes an instance of <see cref="CommandInput"/>.
         /// </summary>
         public CommandInput(string commandName, IReadOnlyList<CommandOptionInput> options)
+            : this(commandName, EmptyDirectives, options)
         {
-            CommandName = commandName; // can be null
-            Options = options.GuardNotNull(nameof(options));
         }
 
         /// <summary>
@@ -41,15 +77,7 @@ namespace CliFx.Models
         /// Initializes an instance of <see cref="CommandInput"/>.
         /// </summary>
         public CommandInput(string commandName)
-            : this(commandName, new CommandOptionInput[0])
-        {
-        }
-
-        /// <summary>
-        /// Initializes an instance of <see cref="CommandInput"/>.
-        /// </summary>
-        public CommandInput()
-            : this(null, new CommandOptionInput[0])
+            : this(commandName, EmptyOptions)
         {
         }
 
@@ -61,6 +89,12 @@ namespace CliFx.Models
             if (!CommandName.IsNullOrWhiteSpace())
                 buffer.Append(CommandName);
 
+            foreach (var directive in Directives)
+            {
+                buffer.AppendIfNotEmpty(' ');
+                buffer.Append(directive);
+            }
+
             foreach (var option in Options)
             {
                 buffer.AppendIfNotEmpty(' ');
@@ -73,9 +107,13 @@ namespace CliFx.Models
 
     public partial class CommandInput
     {
+        private static readonly IReadOnlyList<string> EmptyDirectives = new string[0];
+        private static readonly IReadOnlyList<CommandOptionInput> EmptyOptions = new CommandOptionInput[0];
+        private static readonly IReadOnlyDictionary<string, string> EmptyEnvironmentVariables = new Dictionary<string, string>();
+
         /// <summary>
         /// Empty input.
         /// </summary>
-        public static CommandInput Empty { get; } = new CommandInput();
+        public static CommandInput Empty { get; } = new CommandInput(EmptyOptions);
     }
 }

CliFx/Models/CommandOptionInput.cs

@@ -7,7 +7,7 @@ namespace CliFx.Models
     /// <summary>
     /// Parsed option from command line input.
     /// </summary>
-    public class CommandOptionInput
+    public partial class CommandOptionInput
     {
         /// <summary>
         /// Specified option alias.
@@ -40,7 +40,7 @@ namespace CliFx.Models
         /// Initializes an instance of <see cref="CommandOptionInput"/>.
         /// </summary>
         public CommandOptionInput(string alias)
-            : this(alias, new string[0])
+            : this(alias, EmptyValues)
         {
         }
 
@@ -70,4 +70,9 @@ namespace CliFx.Models
             return buffer.ToString();
         }
     }
+
+    public partial class CommandOptionInput
+    {
+        private static readonly IReadOnlyList<string> EmptyValues = new string[0];
+    }
 }

CliFx/Models/CommandOptionSchema.cs

@@ -34,16 +34,22 @@ namespace CliFx.Models
         /// </summary>
         public string Description { get; }
 
+        /// <summary>
+        /// Optional environment variable name that will be used as fallback value if no option value is specified.
+        /// </summary>
+        public string EnvironmentVariableName { get; }
+
         /// <summary>
         /// Initializes an instance of <see cref="CommandOptionSchema"/>.
         /// </summary>
-        public CommandOptionSchema(PropertyInfo property, string name, char? shortName, bool isRequired, string description)
+        public CommandOptionSchema(PropertyInfo property, string name, char? shortName, bool isRequired, string description, string environmentVariableName)
         {
             Property = property; // can be null
             Name = name; // can be null
             ShortName = shortName; // can be null
             IsRequired = isRequired;
             Description = description; // can be null
+            EnvironmentVariableName = environmentVariableName; //can be null
         }
 
         /// <inheritdoc />
@@ -75,9 +81,9 @@ namespace CliFx.Models
         // ...in CliApplication (when reading) and HelpTextRenderer (when writing).
 
         internal static CommandOptionSchema HelpOption { get; } =
-            new CommandOptionSchema(null, "help", 'h', false, "Shows help text.");
+            new CommandOptionSchema(null, "help", 'h', false, "Shows help text.", null);
 
         internal static CommandOptionSchema VersionOption { get; } =
-            new CommandOptionSchema(null, "version", null, false, "Shows version information.");
+            new CommandOptionSchema(null, "version", null, false, "Shows version information.", null);
     }
 }

CliFx/Models/Extensions.cs

@@ -1,7 +1,7 @@
-using System;
+using CliFx.Internal;
+using System;
 using System.Collections.Generic;
 using System.Linq;
-using CliFx.Internal;
 
 namespace CliFx.Models
 {
@@ -71,16 +71,16 @@ namespace CliFx.Models
 
             return matchesByName || matchesByShortName;
         }
-        
-        /// <summary>
-        /// Finds an option that matches specified alias, or null if not found.
-        /// </summary>
-        public static CommandOptionSchema FindByAlias(this IReadOnlyList<CommandOptionSchema> optionSchemas, string alias)
-        {
-            optionSchemas.GuardNotNull(nameof(optionSchemas));
-            alias.GuardNotNull(nameof(alias));
 
-            return optionSchemas.FirstOrDefault(o => o.MatchesAlias(alias));
+        /// <summary>
+        /// Finds an option input that matches the option schema specified, or null if not found.
+        /// </summary>
+        public static CommandOptionInput FindByOptionSchema(this IReadOnlyList<CommandOptionInput> optionInputs, CommandOptionSchema optionSchema)
+        {
+            optionInputs.GuardNotNull(nameof(optionInputs));
+            optionSchema.GuardNotNull(nameof(optionSchema));
+
+            return optionInputs.FirstOrDefault(o => optionSchema.MatchesAlias(o.Alias));
         }
 
         /// <summary>
@@ -109,26 +109,42 @@ namespace CliFx.Models
         }
 
         /// <summary>
-        /// Gets whether help was requested in the input.
+        /// Gets whether debug directive was specified in the input.
         /// </summary>
-        public static bool IsHelpRequested(this CommandInput commandInput)
+        public static bool IsDebugDirectiveSpecified(this CommandInput commandInput)
+        {
+            commandInput.GuardNotNull(nameof(commandInput));
+            return commandInput.Directives.Contains("debug", StringComparer.OrdinalIgnoreCase);
+        }
+
+        /// <summary>
+        /// Gets whether preview directive was specified in the input.
+        /// </summary>
+        public static bool IsPreviewDirectiveSpecified(this CommandInput commandInput)
+        {
+            commandInput.GuardNotNull(nameof(commandInput));
+            return commandInput.Directives.Contains("preview", StringComparer.OrdinalIgnoreCase);
+        }
+
+        /// <summary>
+        /// Gets whether help option was specified in the input.
+        /// </summary>
+        public static bool IsHelpOptionSpecified(this CommandInput commandInput)
         {
             commandInput.GuardNotNull(nameof(commandInput));
 
             var firstOption = commandInput.Options.FirstOrDefault();
-
             return firstOption != null && CommandOptionSchema.HelpOption.MatchesAlias(firstOption.Alias);
         }
 
         /// <summary>
-        /// Gets whether version information was requested in the input.
+        /// Gets whether version option was specified in the input.
         /// </summary>
-        public static bool IsVersionRequested(this CommandInput commandInput)
+        public static bool IsVersionOptionSpecified(this CommandInput commandInput)
         {
             commandInput.GuardNotNull(nameof(commandInput));
 
             var firstOption = commandInput.Options.FirstOrDefault();
-
             return firstOption != null && CommandOptionSchema.VersionOption.MatchesAlias(firstOption.Alias);
         }
 

CliFx/Services/CommandInitializer.cs

@@ -11,20 +11,30 @@ namespace CliFx.Services
     public class CommandInitializer : ICommandInitializer
     {
         private readonly ICommandOptionInputConverter _commandOptionInputConverter;
+        private readonly IEnvironmentVariablesParser _environmentVariablesParser;
 
         /// <summary>
         /// Initializes an instance of <see cref="CommandInitializer"/>.
         /// </summary>
-        public CommandInitializer(ICommandOptionInputConverter commandOptionInputConverter)
+        public CommandInitializer(ICommandOptionInputConverter commandOptionInputConverter, IEnvironmentVariablesParser environmentVariablesParser)
         {
             _commandOptionInputConverter = commandOptionInputConverter.GuardNotNull(nameof(commandOptionInputConverter));
+            _environmentVariablesParser = environmentVariablesParser.GuardNotNull(nameof(environmentVariablesParser));
+        }
+
+        /// <summary>
+        /// Initializes an instance of <see cref="CommandInitializer"/>.
+        /// </summary>
+        public CommandInitializer(IEnvironmentVariablesParser environmentVariablesParser)
+            : this(new CommandOptionInputConverter(), environmentVariablesParser)
+        {
         }
 
         /// <summary>
         /// Initializes an instance of <see cref="CommandInitializer"/>.
         /// </summary>
         public CommandInitializer()
-            : this(new CommandOptionInputConverter())
+            : this(new CommandOptionInputConverter(), new EnvironmentVariablesParser())
         {
         }
 
@@ -38,15 +48,28 @@ namespace CliFx.Services
             // Keep track of unset required options to report an error at a later stage
             var unsetRequiredOptions = commandSchema.Options.Where(o => o.IsRequired).ToList();
 
-            // Set command options
-            foreach (var optionInput in commandInput.Options)
+            //Set command options
+            foreach (var optionSchema in commandSchema.Options)
             {
-                // Find matching option schema for this option input
-                var optionSchema = commandSchema.Options.FindByAlias(optionInput.Alias);
-                if (optionSchema == null)
+                //Find matching option input
+                var optionInput = commandInput.Options.FindByOptionSchema(optionSchema);
+
+                //If no option input is available fall back to environment variable values
+                if (optionInput == null && !optionSchema.EnvironmentVariableName.IsNullOrWhiteSpace())
+                {
+                    var fallbackEnvironmentVariableExists = commandInput.EnvironmentVariables.ContainsKey(optionSchema.EnvironmentVariableName);
+
+                    //If no environment variable is found or there is no valid value for this option skip it
+                    if (!fallbackEnvironmentVariableExists || commandInput.EnvironmentVariables[optionSchema.EnvironmentVariableName].IsNullOrWhiteSpace())
+                        continue;
+
+                    optionInput = _environmentVariablesParser.GetCommandOptionInputFromEnvironmentVariable(commandInput.EnvironmentVariables[optionSchema.EnvironmentVariableName], optionSchema);
+                }
+
+                //No fallback available and no option input was specified, skip option
+                if (optionInput == null)
                     continue;
 
-                // Convert option to the type of the underlying property
                 var convertedValue = _commandOptionInputConverter.ConvertOptionInput(optionInput, optionSchema.Property.PropertyType);
 
                 // Set value of the underlying property
@@ -61,7 +84,7 @@ namespace CliFx.Services
             if (unsetRequiredOptions.Any())
             {
                 var unsetRequiredOptionNames = unsetRequiredOptions.Select(o => o.GetAliases().FirstOrDefault()).JoinToString(", ");
-                throw new MissingCommandOptionInputException($"One or more required options were not set: {unsetRequiredOptionNames}.");
+                throw new CliFxException($"One or more required options were not set: {unsetRequiredOptionNames}.");
             }
         }
     }

CliFx/Services/CommandInputParser.cs

@@ -12,14 +12,36 @@ namespace CliFx.Services
     /// </summary>
     public class CommandInputParser : ICommandInputParser
     {
+        private readonly IEnvironmentVariablesProvider _environmentVariablesProvider;
+
+        /// <summary>
+        /// Initializes an instance of <see cref="CommandInputParser"/>
+        /// </summary>
+        public CommandInputParser(IEnvironmentVariablesProvider environmentVariablesProvider)
+        {
+            environmentVariablesProvider.GuardNotNull(nameof(environmentVariablesProvider));
+
+            _environmentVariablesProvider = environmentVariablesProvider;
+        }
+
+        /// <summary>
+        /// Initializes an instance of <see cref="CommandInputParser"/>
+        /// </summary>
+        public CommandInputParser()
+            : this(new EnvironmentVariablesProvider())
+        {
+        }
+
         /// <inheritdoc />
         public CommandInput ParseCommandInput(IReadOnlyList<string> commandLineArguments)
         {
             commandLineArguments.GuardNotNull(nameof(commandLineArguments));
 
             var commandNameBuilder = new StringBuilder();
+            var directives = new List<string>();
             var optionsDic = new Dictionary<string, List<string>>();
 
+            // Option aliases and values are parsed in pairs so we need to keep track of last alias
             var lastOptionAlias = "";
 
             foreach (var commandLineArgument in commandLineArguments)
@@ -34,7 +56,7 @@ namespace CliFx.Services
                         optionsDic[lastOptionAlias] = new List<string>();
                 }
 
-                // Encountered short option name or multiple thereof
+                // Encountered short option name or multiple short option names
                 else if (commandLineArgument.StartsWith("-", StringComparison.OrdinalIgnoreCase))
                 {
                     // Handle stacked options
@@ -48,11 +70,22 @@ namespace CliFx.Services
                     }
                 }
 
-                // Encountered command name or part thereof
+                // Encountered directive or (part of) command name
                 else if (lastOptionAlias.IsNullOrWhiteSpace())
                 {
-                    commandNameBuilder.AppendIfNotEmpty(' ');
-                    commandNameBuilder.Append(commandLineArgument);
+                    if (commandLineArgument.StartsWith("[", StringComparison.OrdinalIgnoreCase) &&
+                        commandLineArgument.EndsWith("]", StringComparison.OrdinalIgnoreCase))
+                    {
+                        // Extract directive
+                        var directive = commandLineArgument.Substring(1, commandLineArgument.Length - 2);
+
+                        directives.Add(directive);
+                    }
+                    else
+                    {
+                        commandNameBuilder.AppendIfNotEmpty(' ');
+                        commandNameBuilder.Append(commandLineArgument);
+                    }
                 }
 
                 // Encountered option value
@@ -65,7 +98,9 @@ namespace CliFx.Services
             var commandName = commandNameBuilder.Length > 0 ? commandNameBuilder.ToString() : null;
             var options = optionsDic.Select(p => new CommandOptionInput(p.Key, p.Value)).ToArray();
 
-            return new CommandInput(commandName, options);
+            var environmentVariables = _environmentVariablesProvider.GetEnvironmentVariables();
+
+            return new CommandInput(commandName, directives, options, environmentVariables);
         }
     }
 }

CliFx/Services/CommandOptionInputConverter.cs

@@ -31,8 +31,13 @@ namespace CliFx.Services
         {
         }
 
-        private object ConvertValue(string value, Type targetType)
+        /// <summary>
+        /// Converts a single string value to specified target type.
+        /// </summary>
+        protected virtual object ConvertValue(string value, Type targetType)
         {
+            targetType.GuardNotNull(nameof(targetType));
+
             try
             {
                 // String or object
@@ -108,7 +113,7 @@ namespace CliFx.Services
                     return Enum.Parse(targetType, value, true);
 
                 // Nullable
-                var nullableUnderlyingType = Nullable.GetUnderlyingType(targetType);
+                var nullableUnderlyingType = targetType.GetNullableUnderlyingType();
                 if (nullableUnderlyingType != null)
                     return !value.IsNullOrWhiteSpace() ? ConvertValue(value, nullableUnderlyingType) : null;
 
@@ -126,48 +131,66 @@ namespace CliFx.Services
                 var parseMethod = GetStaticParseMethod(targetType);
                 if (parseMethod != null)
                     return parseMethod.Invoke(null, new object[] {value});
-
-                throw new InvalidCommandOptionInputException($"Can't convert value [{value}] to type [{targetType}].");
             }
             catch (Exception ex)
             {
-                throw new InvalidCommandOptionInputException($"Can't convert value [{value}] to type [{targetType}].", ex);
+                // Wrap and rethrow exceptions that occur when trying to convert the value
+                throw new CliFxException($"Can't convert value [{value}] to type [{targetType}].", ex);
             }
+
+            // Throw if we can't find a way to convert the value
+            throw new CliFxException($"Can't convert value [{value}] to type [{targetType}].");
         }
 
         /// <inheritdoc />
-        public object ConvertOptionInput(CommandOptionInput optionInput, Type targetType)
+        public virtual object ConvertOptionInput(CommandOptionInput optionInput, Type targetType)
         {
             optionInput.GuardNotNull(nameof(optionInput));
             targetType.GuardNotNull(nameof(targetType));
 
-            // Single value
-            if (optionInput.Values.Count <= 1)
+            // Get the underlying type of IEnumerable<T> if it's implemented by the target type.
+            // Ignore string type because it's IEnumerable<T> but we don't treat it as such.
+            var enumerableUnderlyingType = targetType != typeof(string) ? targetType.GetEnumerableUnderlyingType() : null;
+
+            // Convert to a non-enumerable type
+            if (enumerableUnderlyingType == null)
             {
+                // Throw if provided with more than 1 value
+                if (optionInput.Values.Count > 1)
+                {
+                    throw new CliFxException(
+                        $"Can't convert a sequence of values [{optionInput.Values.JoinToString(", ")}] " +
+                        $"to non-enumerable type [{targetType}].");
+                }
+
+                // Retrieve a single value and convert
                 var value = optionInput.Values.SingleOrDefault();
                 return ConvertValue(value, targetType);
             }
-            // Multiple values
+            // Convert to an enumerable type
             else
             {
-                // Determine underlying type of elements inside the target collection type
-                var underlyingType = targetType.GetEnumerableUnderlyingType() ?? typeof(object);
+                // Convert values to the underlying enumerable type and cast it to dynamic array
+                var convertedValues = optionInput.Values
+                    .Select(v => ConvertValue(v, enumerableUnderlyingType))
+                    .ToNonGenericArray(enumerableUnderlyingType);
 
-                // Convert values to that type
-                var convertedValues = optionInput.Values.Select(v => ConvertValue(v, underlyingType)).ToNonGenericArray(underlyingType);
+                // Get the type of produced array
                 var convertedValuesType = convertedValues.GetType();
 
-                // Assignable from array of values (e.g. T[], IReadOnlyList<T>, IEnumerable<T>)
+                // Try to assign the array (works for T[], IReadOnlyList<T>, IEnumerable<T>, etc)
                 if (targetType.IsAssignableFrom(convertedValuesType))
                     return convertedValues;
 
-                // Has a constructor that accepts an array of values (e.g. HashSet<T>, List<T>)
+                // Try to inject the array into the constructor (works for HashSet<T>, List<T>, etc)
                 var arrayConstructor = targetType.GetConstructor(new[] {convertedValuesType});
                 if (arrayConstructor != null)
                     return arrayConstructor.Invoke(new object[] {convertedValues});
 
-                throw new InvalidCommandOptionInputException(
-                    $"Can't convert sequence of values [{optionInput.Values.JoinToString(", ")}] to type [{targetType}].");
+                // Throw if we can't find a way to convert the values
+                throw new CliFxException(
+                    $"Can't convert a sequence of values [{optionInput.Values.JoinToString(", ")}] " +
+                    $"to type [{targetType}].");
             }
         }
     }

CliFx/Services/CommandSchemaResolver.cs

@@ -14,31 +14,55 @@ namespace CliFx.Services
     /// </summary>
     public class CommandSchemaResolver : ICommandSchemaResolver
     {
-        private CommandOptionSchema GetCommandOptionSchema(PropertyInfo optionProperty)
+        private IReadOnlyList<CommandOptionSchema> GetCommandOptionSchemas(Type commandType)
         {
-            var attribute = optionProperty.GetCustomAttribute<CommandOptionAttribute>();
+            var result = new List<CommandOptionSchema>();
 
-            if (attribute == null)
-                return null;
+            foreach (var property in commandType.GetProperties())
+            {
+                var attribute = property.GetCustomAttribute<CommandOptionAttribute>();
 
-            return new CommandOptionSchema(optionProperty,
-                attribute.Name,
-                attribute.ShortName,
-                attribute.IsRequired,
-                attribute.Description);
-        }
+                // If an attribute is not set, then it's not an option so we just skip it
+                if (attribute == null)
+                    continue;
 
-        private CommandSchema GetCommandSchema(Type commandType)
-        {
-            // Attribute is optional for commands in order to reduce runtime rule complexity
-            var attribute = commandType.GetCustomAttribute<CommandAttribute>();
+                // Build option schema
+                var optionSchema = new CommandOptionSchema(property,
+                    attribute.Name,
+                    attribute.ShortName,
+                    attribute.IsRequired,
+                    attribute.Description,
+                    attribute.EnvironmentVariableName);
 
-            var options = commandType.GetProperties().Select(GetCommandOptionSchema).ExceptNull().ToArray();
+                // Make sure there are no other options with the same name
+                var existingOptionWithSameName = result
+                    .Where(o => !o.Name.IsNullOrWhiteSpace())
+                    .FirstOrDefault(o => string.Equals(o.Name, optionSchema.Name, StringComparison.OrdinalIgnoreCase));
 
-            return new CommandSchema(commandType,
-                attribute?.Name,
-                attribute?.Description,
-                options);
+                if (existingOptionWithSameName != null)
+                {
+                    throw new CliFxException(
+                        $"Command type [{commandType}] has options defined with the same name: " +
+                        $"[{existingOptionWithSameName.Property}] and [{optionSchema.Property}].");
+                }
+
+                // Make sure there are no other options with the same short name
+                var existingOptionWithSameShortName = result
+                    .Where(o => o.ShortName != null)
+                    .FirstOrDefault(o => o.ShortName == optionSchema.ShortName);
+
+                if (existingOptionWithSameShortName != null)
+                {
+                    throw new CliFxException(
+                        $"Command type [{commandType}] has options defined with the same short name: " +
+                        $"[{existingOptionWithSameShortName.Property}] and [{optionSchema.Property}].");
+                }
+
+                // Add schema to list
+                result.Add(optionSchema);
+            }
+
+            return result;
         }
 
         /// <inheritdoc />
@@ -46,82 +70,55 @@ namespace CliFx.Services
         {
             commandTypes.GuardNotNull(nameof(commandTypes));
 
-            // Get command schemas
-            var commandSchemas = commandTypes.Select(GetCommandSchema).ToArray();
-
-            // Throw if there are no commands defined
-            if (!commandSchemas.Any())
+            // Make sure there's at least one command defined
+            if (!commandTypes.Any())
             {
-                throw new InvalidCommandSchemaException("There are no commands defined.");
+                throw new CliFxException("There are no commands defined.");
             }
 
-            // Throw if there are multiple commands with the same name
-            var nonUniqueCommandNames = commandSchemas
-                .Select(c => c.Name)
-                .GroupBy(i => i, StringComparer.OrdinalIgnoreCase)
-                .Where(g => g.Count() >= 2)
-                .SelectMany(g => g)
-                .Distinct(StringComparer.OrdinalIgnoreCase)
-                .ToArray();
+            var result = new List<CommandSchema>();
 
-            foreach (var commandName in nonUniqueCommandNames)
+            foreach (var commandType in commandTypes)
             {
-                throw new InvalidCommandSchemaException(!commandName.IsNullOrWhiteSpace()
-                    ? $"There are multiple commands defined with name [{commandName}]."
-                    : "There are multiple default commands defined.");
-            }
-
-            // Throw if there are commands that don't implement ICommand
-            var nonImplementedCommandNames = commandSchemas
-                .Where(c => !c.Type.Implements(typeof(ICommand)))
-                .Select(c => c.Name)
-                .Distinct(StringComparer.OrdinalIgnoreCase)
-                .ToArray();
-
-            foreach (var commandName in nonImplementedCommandNames)
-            {
-                throw new InvalidCommandSchemaException(!commandName.IsNullOrWhiteSpace()
-                    ? $"Command [{commandName}] doesn't implement ICommand."
-                    : "Default command doesn't implement ICommand.");
-            }
-
-            // Throw if there are multiple options with the same name inside the same command
-            foreach (var commandSchema in commandSchemas)
-            {
-                var nonUniqueOptionNames = commandSchema.Options
-                    .Where(o => !o.Name.IsNullOrWhiteSpace())
-                    .Select(o => o.Name)
-                    .GroupBy(i => i, StringComparer.OrdinalIgnoreCase)
-                    .Where(g => g.Count() >= 2)
-                    .SelectMany(g => g)
-                    .Distinct(StringComparer.OrdinalIgnoreCase)
-                    .ToArray();
-
-                foreach (var optionName in nonUniqueOptionNames)
+                // Make sure command type implements ICommand.
+                if (!commandType.Implements(typeof(ICommand)))
                 {
-                    throw new InvalidCommandSchemaException(!commandSchema.Name.IsNullOrWhiteSpace()
-                        ? $"There are multiple options defined with name [{optionName}] on command [{commandSchema.Name}]."
-                        : $"There are multiple options defined with name [{optionName}] on default command.");
+                    throw new CliFxException($"Command type [{commandType}] must implement {typeof(ICommand)}.");
                 }
 
-                var nonUniqueOptionShortNames = commandSchema.Options
-                    .Where(o => o.ShortName != null)
-                    .Select(o => o.ShortName.Value)
-                    .GroupBy(i => i)
-                    .Where(g => g.Count() >= 2)
-                    .SelectMany(g => g)
-                    .Distinct()
-                    .ToArray();
+                // Get attribute
+                var attribute = commandType.GetCustomAttribute<CommandAttribute>();
 
-                foreach (var optionShortName in nonUniqueOptionShortNames)
+                // Make sure attribute is set
+                if (attribute == null)
                 {
-                    throw new InvalidCommandSchemaException(!commandSchema.Name.IsNullOrWhiteSpace()
-                        ? $"There are multiple options defined with short name [{optionShortName}] on command [{commandSchema.Name}]."
-                        : $"There are multiple options defined with short name [{optionShortName}] on default command.");
+                    throw new CliFxException($"Command type [{commandType}] must be annotated with [{typeof(CommandAttribute)}].");
                 }
+
+                // Get option schemas
+                var optionSchemas = GetCommandOptionSchemas(commandType);
+
+                // Build command schema
+                var commandSchema = new CommandSchema(commandType,
+                    attribute.Name,
+                    attribute.Description,
+                    optionSchemas);
+
+                // Make sure there are no other commands with the same name
+                var existingCommandWithSameName = result
+                    .FirstOrDefault(c => string.Equals(c.Name, commandSchema.Name, StringComparison.OrdinalIgnoreCase));
+
+                if (existingCommandWithSameName != null)
+                {
+                    throw new CliFxException(
+                        $"Command type [{existingCommandWithSameName.Type}] has the same name as another command type [{commandType}].");
+                }
+
+                // Add schema to list
+                result.Add(commandSchema);
             }
 
-            return commandSchemas;
+            return result;
         }
     }
 }

CliFx/Services/EnvironmentVariablesParser.cs

@@ -0,0 +1,30 @@
+using System.IO;
+using System.Linq;
+using CliFx.Internal;
+using CliFx.Models;
+
+namespace CliFx.Services
+{
+    /// <inheritdoct />
+    public class EnvironmentVariablesParser : IEnvironmentVariablesParser
+    {
+        /// <inheritdoct />
+        public CommandOptionInput GetCommandOptionInputFromEnvironmentVariable(string environmentVariableValue, CommandOptionSchema targetOptionSchema)
+        {
+            environmentVariableValue.GuardNotNull(nameof(environmentVariableValue));
+            targetOptionSchema.GuardNotNull(nameof(targetOptionSchema));
+
+            //If the option is not a collection do not split environment variable values
+            var optionIsCollection = targetOptionSchema.Property.PropertyType.IsCollection();
+
+            if (!optionIsCollection) return new CommandOptionInput(targetOptionSchema.EnvironmentVariableName, environmentVariableValue);
+
+            //If the option is a collection split the values using System separator, empty values are discarded
+            var environmentVariableValues = environmentVariableValue.Split(Path.PathSeparator)
+                .Where(v => !v.IsNullOrWhiteSpace())
+                .ToList();
+
+            return new CommandOptionInput(targetOptionSchema.EnvironmentVariableName, environmentVariableValues);
+        }
+    }
+}

CliFx/Services/EnvironmentVariablesProvider.cs

@@ -0,0 +1,36 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Security;
+
+namespace CliFx.Services
+{
+    /// <inheritdoc />
+    public class EnvironmentVariablesProvider : IEnvironmentVariablesProvider
+    {
+        /// <inheritdoc />
+        public IReadOnlyDictionary<string, string> GetEnvironmentVariables()
+        {
+            try
+            {
+                var environmentVariables = Environment.GetEnvironmentVariables();
+
+                //Constructing the dictionary manually allows to specify a key comparer that ignores case
+                //This allows to ignore casing when looking for a fallback environment variable of an option
+                var environmentVariablesAsDictionary = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
+
+                //Type DictionaryEntry must be explicitly used otherwise it will enumerate as a collection of objects
+                foreach (DictionaryEntry environmentVariable in environmentVariables)
+                {
+                    environmentVariablesAsDictionary.Add(environmentVariable.Key.ToString(), environmentVariable.Value.ToString());
+                }
+
+                return environmentVariablesAsDictionary;
+            }
+            catch (SecurityException)
+            {
+                return new Dictionary<string, string>();
+            }
+        }
+    }
+}

CliFx/Services/Extensions.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using CliFx.Internal;
 
 namespace CliFx.Services
@@ -50,5 +51,25 @@ namespace CliFx.Services
 
             console.WithForegroundColor(foregroundColor, () => console.WithBackgroundColor(backgroundColor, action));
         }
+
+        /// <summary>
+        /// Gets wether a string representing an environment variable value is escaped (i.e.: surrounded by double quotation marks)
+        /// </summary>
+        public static bool IsEnvironmentVariableEscaped(this string environmentVariableValue)
+        {
+            environmentVariableValue.GuardNotNull(nameof(environmentVariableValue));
+
+            return environmentVariableValue.StartsWith("\"") && environmentVariableValue.EndsWith("\"");
+        }
+
+        /// <summary>
+        /// Gets wether the <see cref="Type"/> supplied is a collection implementing <see cref="IEnumerable{T}"/>
+        /// </summary>
+        public static bool IsCollection(this Type type)
+        {
+            type.GuardNotNull(nameof(type));
+
+            return type != typeof(string) && type.GetEnumerableUnderlyingType() != null;
+        }
     }
 }

CliFx/Services/HelpTextRenderer.cs

@@ -169,8 +169,14 @@ namespace CliFx.Services
                 // Header
                 RenderHeader("Options");
 
+                // Order options and append built-in options
+                var allOptionSchemas = source.TargetCommandSchema.Options
+                    .OrderByDescending(o => o.IsRequired)
+                    .Concat(builtInOptionSchemas)
+                    .ToArray();
+
                 // Options
-                foreach (var optionSchema in source.TargetCommandSchema.Options.Concat(builtInOptionSchemas))
+                foreach (var optionSchema in allOptionSchemas)
                 {
                     // Is required
                     if (optionSchema.IsRequired)

CliFx/Services/ICommandFactory.cs

@@ -1,5 +1,4 @@
-using System;
-using CliFx.Models;
+using CliFx.Models;
 
 namespace CliFx.Services
 {

CliFx/Services/IConsole.cs

@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using System.Threading;
 
 namespace CliFx.Services
 {
@@ -52,5 +53,11 @@ namespace CliFx.Services
         /// Resets foreground and background color to default values.
         /// </summary>
         void ResetColor();
+
+        /// <summary>
+        /// Provides token that cancels when application cancellation is requested.
+        /// Subsequent calls return the same token.
+        /// </summary>
+        CancellationToken GetCancellationToken();
     }
 }

CliFx/Services/IEnvironmentVariablesParser.cs

@@ -0,0 +1,15 @@
+using CliFx.Models;
+
+namespace CliFx.Services
+{
+    /// <summary>
+    /// Parses environment variable values
+    /// </summary>
+    public interface IEnvironmentVariablesParser
+    {
+        /// <summary>
+        /// Parse an environment variable value and converts it to a <see cref="CommandOptionInput"/> 
+        /// </summary>
+        CommandOptionInput GetCommandOptionInputFromEnvironmentVariable(string environmentVariableValue, CommandOptionSchema targetOptionSchema);
+    }
+}

CliFx/Services/IEnvironmentVariablesProvider.cs

@@ -0,0 +1,16 @@
+using System.Collections.Generic;
+
+namespace CliFx.Services
+{
+    /// <summary>
+    /// Provides environment variable values
+    /// </summary>
+    public interface IEnvironmentVariablesProvider
+    {
+        /// <summary>
+        /// Returns all the environment variables available.
+        /// </summary>
+        /// <remarks>If the User is not allowed to read environment variables it will return an empty dictionary.</remarks>
+        IReadOnlyDictionary<string, string> GetEnvironmentVariables();
+    }
+}

CliFx/Services/SystemConsole.cs

@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using System.Threading;
 
 namespace CliFx.Services
 {
@@ -8,6 +9,8 @@ namespace CliFx.Services
     /// </summary>
     public class SystemConsole : IConsole
     {
+        private CancellationTokenSource _cancellationTokenSource;
+        
         /// <inheritdoc />
         public TextReader Input => Console.In;
 
@@ -42,5 +45,26 @@ namespace CliFx.Services
 
         /// <inheritdoc />
         public void ResetColor() => Console.ResetColor();
+
+        /// <inheritdoc />
+        public CancellationToken GetCancellationToken()
+        {
+            if (_cancellationTokenSource is null)
+            {
+                _cancellationTokenSource = new CancellationTokenSource();
+
+                // Subscribe to CancelKeyPress event with cancellation token source
+                // Kills app on second cancellation (hard cancellation)
+                Console.CancelKeyPress += (_, args) =>
+                {
+                    if (_cancellationTokenSource.IsCancellationRequested)
+                        return;
+                    args.Cancel = true;
+                    _cancellationTokenSource.Cancel();
+                };
+            }
+
+            return _cancellationTokenSource.Token;
+        }
     }
 }

CliFx/Services/VirtualConsole.cs

@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using System.Threading;
 using CliFx.Internal;
 
 namespace CliFx.Services
@@ -11,23 +12,25 @@ namespace CliFx.Services
     /// </summary>
     public class VirtualConsole : IConsole
     {
+        private readonly CancellationToken _cancellationToken;
+
         /// <inheritdoc />
         public TextReader Input { get; }
 
         /// <inheritdoc />
-        public bool IsInputRedirected => true;
+        public bool IsInputRedirected { get; }
 
         /// <inheritdoc />
         public TextWriter Output { get; }
 
         /// <inheritdoc />
-        public bool IsOutputRedirected => true;
+        public bool IsOutputRedirected { get; }
 
         /// <inheritdoc />
         public TextWriter Error { get; }
 
         /// <inheritdoc />
-        public bool IsErrorRedirected => true;
+        public bool IsErrorRedirected { get; }
 
         /// <inheritdoc />
         public ConsoleColor ForegroundColor { get; set; } = ConsoleColor.Gray;
@@ -38,19 +41,35 @@ namespace CliFx.Services
         /// <summary>
         /// Initializes an instance of <see cref="VirtualConsole"/>.
         /// </summary>
-        public VirtualConsole(TextReader input, TextWriter output, TextWriter error)
+        public VirtualConsole(TextReader input, bool isInputRedirected,
+            TextWriter output, bool isOutputRedirected,
+            TextWriter error, bool isErrorRedirected,
+            CancellationToken cancellationToken = default)
         {
             Input = input.GuardNotNull(nameof(input));
+            IsInputRedirected = isInputRedirected;
             Output = output.GuardNotNull(nameof(output));
+            IsOutputRedirected = isOutputRedirected;
             Error = error.GuardNotNull(nameof(error));
+            IsErrorRedirected = isErrorRedirected;
+            _cancellationToken = cancellationToken;
+        }
+
+        /// <summary>
+        /// Initializes an instance of <see cref="VirtualConsole"/>.
+        /// </summary>
+        public VirtualConsole(TextReader input, TextWriter output, TextWriter error, 
+            CancellationToken cancellationToken = default)
+            : this(input, true, output, true, error, true, cancellationToken)
+        {
         }
 
         /// <summary>
         /// Initializes an instance of <see cref="VirtualConsole"/> using output stream (stdout) and error stream (stderr).
         /// Input stream (stdin) is replaced with a no-op stub.
         /// </summary>
-        public VirtualConsole(TextWriter output, TextWriter error)
-            : this(TextReader.Null, output, error)
+        public VirtualConsole(TextWriter output, TextWriter error, CancellationToken cancellationToken = default)
+            : this(TextReader.Null, output, error, cancellationToken)
         {
         }
 
@@ -58,8 +77,8 @@ namespace CliFx.Services
         /// Initializes an instance of <see cref="VirtualConsole"/> using output stream (stdout).
         /// Input stream (stdin) and error stream (stderr) are replaced with no-op stubs.
         /// </summary>
-        public VirtualConsole(TextWriter output)
-            : this(output, TextWriter.Null)
+        public VirtualConsole(TextWriter output, CancellationToken cancellationToken = default)
+            : this(output, TextWriter.Null, cancellationToken)
         {
         }
 
@@ -69,5 +88,8 @@ namespace CliFx.Services
             ForegroundColor = ConsoleColor.Gray;
             BackgroundColor = ConsoleColor.Black;
         }
+
+        /// <inheritdoc />
+        public CancellationToken GetCancellationToken() => _cancellationToken;
     }
 }

CliFx/Utilities/Extensions.cs

@@ -0,0 +1,15 @@
+using CliFx.Services;
+
+namespace CliFx.Utilities
+{
+    /// <summary>
+    /// Extensions for <see cref="Utilities"/>.
+    /// </summary>
+    public static class Extensions
+    {
+        /// <summary>
+        /// Creates a <see cref="ProgressTicker"/> bound to this console.
+        /// </summary>
+        public static ProgressTicker CreateProgressTicker(this IConsole console) => new ProgressTicker(console);
+    }
+}

CliFx/Utilities/ProgressTicker.cs

@@ -0,0 +1,50 @@
+using System;
+using CliFx.Services;
+
+namespace CliFx.Utilities
+{
+    /// <summary>
+    /// Utility for rendering current progress to the console that erases and rewrites output on every tick.
+    /// </summary>
+    public class ProgressTicker : IProgress<double>
+    {
+        private readonly IConsole _console;
+
+        private string _lastOutput = "";
+
+        /// <summary>
+        /// Initializes an instance of <see cref="ProgressTicker"/>.
+        /// </summary>
+        public ProgressTicker(IConsole console)
+        {
+            _console = console;
+        }
+
+        private void EraseLastOutput()
+        {
+            for (var i = 0; i < _lastOutput.Length; i++)
+                _console.Output.Write('\b');
+        }
+
+        private void RenderProgress(double progress)
+        {
+            _lastOutput = progress.ToString("P2", _console.Output.FormatProvider);
+            _console.Output.Write(_lastOutput);
+        }
+
+        /// <summary>
+        /// Erases previous output and renders new progress to the console.
+        /// If console's stdout is redirected, this method returns without doing anything.
+        /// </summary>
+        public void Report(double progress)
+        {
+            // We don't do anything if stdout is redirected to avoid polluting output
+            //...when there's no active console window.
+            if (!_console.IsOutputRedirected)
+            {
+                EraseLastOutput();
+                RenderProgress(progress);
+            }
+        }
+    }
+}

Readme.md

@@ -21,21 +21,35 @@ _CliFx is to command line interfaces what ASP.NET Core is to web applications._
 
 - Complete application framework, not just an argument parser
 - Requires minimal amount of code to get started
-- Resolves commands using attributes
+- Resolves commands and options using attributes
 - Handles options of various types, including custom types
 - Supports multi-level command hierarchies
+- Allows cancellation
 - Generates contextual help text
 - Prints errors and routes exit codes on exceptions
-- Highly testable and easy to customize
+- Highly testable and easy to debug
 - Targets .NET Framework 4.5+ and .NET Standard 2.0+
 - No external dependencies
 
-### Currently not implemented
+## Screenshots
 
-- Positional arguments (anonymous options)
-- Auto-completion support
-- Environment variables
-- Runtime directives
+![help screen](.screenshots/help.png)
+
+## Argument syntax
+
+This library employs a variation of the GNU command line argument syntax. Because CliFx uses a context-unaware parser, the syntax rules are generally more consistent and intuitive.
+
+The following examples are valid for any application created with CliFx:
+
+- `myapp --foo bar` sets option `"foo"` to value `"bar"`
+- `myapp -f bar` sets option `'f'` to value `"bar"`
+- `myapp --switch` sets option `"switch"` to value `true`
+- `myapp -s` sets option `'s'` to value `true`
+- `myapp -abc` sets options `'a'`, `'b'` and `'c'` to value `true`
+- `myapp -xqf bar` sets options `'x'` and `'q'` to value `true`, and option `'f'` to value `"bar"`
+- `myapp -i file1.txt file2.txt` sets option `'i'` to a sequence of values `"file1.txt"` and `"file2.txt"`
+- `myapp -i file1.txt -i file2.txt` sets option `'i'` to a sequence of values `"file1.txt"` and `"file2.txt"`
+- `myapp jar new -o cookie` invokes command `jar new` and sets option `'o'` to value `"cookie"`
 
 ## Usage
 
@@ -86,7 +100,7 @@ public class LogCommand : ICommand
 
 By implementing `ICommand` this class also provides `ExecuteAsync` method. This is the method that gets called when the user invokes the command. Its return type is `Task` in order to facilitate asynchronous execution, but if your command runs synchronously you can simply return `Task.CompletedTask`.
 
-The `ExecuteAsync` method also takes an instance of `IConsole` as a parameter. You should use this abstraction to interact with the console instead of calling `System.Console` so that your commands are testable.
+The `ExecuteAsync` method also takes an instance of `IConsole` as a parameter. You should use the `console` parameter in places where you would normally use `System.Console`, in order to make your command testable.
 
 Finally, the command defined above can be executed from the command line in one of the following ways:
 
@@ -114,6 +128,34 @@ When resolving options, CliFx can convert string values obtained from the comman
 
 If you want to define an option of your own type, the easiest way to do it is to make sure that your type is string-initializable, as explained above.
 
+It is also possible to configure the application to use your own converter, by calling `UseCommandOptionInputConverter` method on `CliApplicationBuilder`.
+
+```c#
+var app = new CliApplicationBuilder()
+    .AddCommandsFromThisAssembly()
+    .UseCommandOptionInputConverter(new MyConverter())
+    .Build();
+```
+
+The converter class must implement `ICommandOptionInputConverter` but you can also derive from `CommandOptionInputConverter` to extend the default behavior.
+
+```c#
+public class MyConverter : CommandOptionInputConverter
+{
+    protected override object ConvertValue(string value, Type targetType)
+    {
+        // Custom conversion for MyType
+        if (targetType == typeof(MyType))
+        {
+            // ...
+        }
+
+        // Default behavior for other types
+        return base.ConvertValue(value, targetType);
+    }
+}
+```
+
 ### Reporting errors
 
 You may have noticed that commands in CliFx don't return exit codes. This is by design as exit codes are considered a higher-level concern and thus handled by `CliApplication`, not by individual commands.
@@ -174,6 +216,30 @@ public class SecondSubCommand : ICommand
 }
 ```
 
+### Cancellation
+
+It is possible to gracefully cancel execution of a command and preform any necessary cleanup. By default an app gets forcefully killed when it receives an interrupt signal (Ctrl+C or Ctrl+Break). You can call `console.GetCancellationToken()` to override the default behavior and get `CancellationToken` that represents the first interrupt signal. Second interrupt signal terminates an app immediately. Note that the code that executes before the first call to `GetCancellationToken` will not be cancellation aware.
+
+You can pass `CancellationToken` around and check its state. 
+
+Cancelled or terminated app returns non-zero exit code.
+
+```c#
+[Command("cancel")]
+public class CancellableCommand : ICommand
+{
+    public async Task ExecuteAsync(IConsole console)
+    {
+        console.Output.WriteLine("Printed");
+
+        // Long-running cancellable operation that throws when canceled
+        await Task.Delay(Timeout.InfiniteTimeSpan, console.GetCancellationToken());
+
+        console.Output.WriteLine("Never printed");
+    }
+}
+```
+
 ### Dependency injection
 
 CliFx uses an implementation of `ICommandFactory` to initialize commands and by default it only works with types that have parameterless constructors.
@@ -262,6 +328,21 @@ var app = new CliApplicationBuilder()
     .Build();
 ```
 
+### Report progress
+
+CliFx comes with a simple utility for reporting progress to the console, `ProgressTicker`, which renders progress in-place on every tick.
+
+It implements a well-known `IProgress<double>` interface so you can pass it to methods that are aware of this abstraction.
+
+To avoid polluting output when it's not bound to a console, `ProgressTicker` will simply no-op if stdout is redirected.
+
+```c#
+var progressTicker = console.CreateProgressTicker();
+
+for (var i = 0.0; i <= 1; i += 0.01)
+    progressTicker.Report(i);
+```
+
 ### Testing
 
 CliFx makes it really easy to test your commands thanks to the `IConsole` interface.
@@ -344,15 +425,32 @@ public async Task ConcatCommand_Test()
 }
 ```
 
+### Debug and preview mode
+
+When troubleshooting issues, you may find it useful to run your app in debug or preview mode. To do it, simply pass the corresponding directive to your app along with other command line arguments, e.g.: `myapp [debug] user add -n "John Doe" -e john.doe@example.com`
+
+If your application is ran in debug mode (`[debug]` directive), it will wait for debugger to be attached before proceeding. This is useful for debugging apps that were ran outside of your IDE.
+
+If preview mode is specified (`[preview]` directive), the app will print consumed command line arguments as they were parsed. This is useful when troubleshooting issues related to option parsing.
+
+You can also disallow these directives, e.g. when running in production, by calling `AllowDebugMode` and `AllowPreviewMode` methods on `CliApplicationBuilder`.
+
+```c#
+var app = new CliApplicationBuilder()
+    .AddCommandsFromThisAssembly()
+    .AllowDebugMode(true) // allow debug mode
+    .AllowPreviewMode(false) // disallow preview mode
+    .Build();
+```
+
 ## Benchmarks
 
-CliFx has the smallest performance overhead compared to other command line parsers and frameworks.
-Below you can see a table comparing execution times of a simple command across different libraries.
+Here's how CliFx's execution overhead compares to that of other libraries.
 
 ```ini
-BenchmarkDotNet=v0.11.5, OS=Windows 10.0.14393.0 (1607/AnniversaryUpdate/Redstone1)
+BenchmarkDotNet=v0.11.5, OS=Windows 10.0.14393.3144 (1607/AnniversaryUpdate/Redstone1)
 Intel Core i5-4460 CPU 3.20GHz (Haswell), 1 CPU, 4 logical and 4 physical cores
-Frequency=3125008 Hz, Resolution=319.9992 ns, Timer=TSC
+Frequency=3125011 Hz, Resolution=319.9989 ns, Timer=TSC
 .NET Core SDK=2.2.401
   [Host] : .NET Core 2.2.6 (CoreCLR 4.6.27817.03, CoreFX 4.6.27818.02), 64bit RyuJIT
   Core   : .NET Core 2.2.6 (CoreCLR 4.6.27817.03, CoreFX 4.6.27818.02), 64bit RyuJIT
@@ -362,10 +460,12 @@ Job=Core  Runtime=Core
 
 |                               Method |      Mean |     Error |    StdDev | Ratio | RatioSD | Rank |
 |------------------------------------- |----------:|----------:|----------:|------:|--------:|-----:|
-|                                CliFx |  39.47 us | 0.7490 us | 0.9198 us |  1.00 |    0.00 |    1 |
-|                   System.CommandLine | 153.98 us | 0.7112 us | 0.6652 us |  3.90 |    0.09 |    2 |
-| McMaster.Extensions.CommandLineUtils | 180.36 us | 3.5893 us | 6.7416 us |  4.59 |    0.16 |    3 |
-|                            PowerArgs | 427.54 us | 6.9006 us | 6.4548 us | 10.82 |    0.26 |    4 |
+|                                CliFx |  31.29 us | 0.6147 us | 0.7774 us |  1.00 |    0.00 |    2 |
+|                   System.CommandLine | 184.44 us | 3.4993 us | 4.0297 us |  5.90 |    0.21 |    4 |
+| McMaster.Extensions.CommandLineUtils | 165.50 us | 1.4805 us | 1.3124 us |  5.33 |    0.13 |    3 |
+|                    CommandLineParser |  26.65 us | 0.5530 us | 0.5679 us |  0.85 |    0.03 |    1 |
+|                            PowerArgs | 405.44 us | 7.7133 us | 9.1821 us | 12.96 |    0.47 |    6 |
+|                                Clipr | 220.82 us | 4.4567 us | 4.9536 us |  7.06 |    0.25 |    5 |
 
 ## Philosophy
 
@@ -394,7 +494,6 @@ CliFx is made out of "Cli" for "Command Line Interface" and "Fx" for "Framework"
 ## Libraries used
 
 - [NUnit](https://github.com/nunit/nunit)
-- [CliWrap](https://github.com/Tyrrrz/CliWrap)
 - [FluentAssertions](https://github.com/fluentassertions/fluentassertions)
 - [Newtonsoft.Json](https://github.com/JamesNK/Newtonsoft.Json)
 - [BenchmarkDotNet](https://github.com/dotnet/BenchmarkDotNet)
@@ -402,4 +501,4 @@ CliFx is made out of "Cli" for "Command Line Interface" and "Fx" for "Framework"
 
 ## Donate
 
-If you really like my projects and want to support me, consider donating to me on [Patreon](https://patreon.com/tyrrrz) or [BuyMeACoffee](https://buymeacoffee.com/tyrrrz). All donations are optional and are greatly appreciated. 🙏
+If you really like my projects and want to support me, consider donating to me on [Patreon](https://patreon.com/tyrrrz) or [BuyMeACoffee](https://buymeacoffee.com/tyrrrz). All donations are optional and are greatly appreciated. 🙏

appveyor.yml

@@ -1,6 +1,6 @@
 version: '{build}'
 
-image: Visual Studio 2017
+image: Visual Studio 2019
 configuration: Release
 
 before_build: