diff --git a/bin/adventofcode2025.dart b/bin/adventofcode2025.dart
index 5043c7b..1980214 100644
--- a/bin/adventofcode2025.dart
+++ b/bin/adventofcode2025.dart
@@ -1,6 +1,7 @@
 import 'package:adventofcode2025/day1/command.dart' as day1;
 import 'package:adventofcode2025/day2/command.dart' as day2;
 import 'package:adventofcode2025/day3/command.dart' as day3;
+import 'package:adventofcode2025/day4/command.dart' as day4;
 
 import 'package:args/command_runner.dart';
 
@@ -9,5 +10,6 @@ void main(List<String> arguments) {
     ..addCommand(day1.Day1Command())
     ..addCommand(day2.Day2Command())
     ..addCommand(day3.Day3Command())
+    ..addCommand(day4.Day4Command())
     ..run(arguments);
 }
diff --git a/lib/day1/command.dart b/lib/day1/command.dart
index 2f8ed75..656eafa 100644
--- a/lib/day1/command.dart
+++ b/lib/day1/command.dart
@@ -58,6 +58,7 @@ class Day1Command extends Command {
       print(
         "Expected 1 positional arguments, found ${argResults!.rest.length}",
       );
+      exit(1);
     }
     var fileName = argResults!.rest[0];
 
diff --git a/lib/day2/command.dart b/lib/day2/command.dart
index 52baa02..f118b28 100644
--- a/lib/day2/command.dart
+++ b/lib/day2/command.dart
@@ -26,6 +26,7 @@ class Day2Command extends Command {
       print(
         "Expected 1 positional arguments, found ${argResults!.rest.length}",
       );
+      exit(1);
     }
     var filePath = argResults!.rest[0];
 
diff --git a/lib/day3/command.dart b/lib/day3/command.dart
index cb85e6a..85119af 100644
--- a/lib/day3/command.dart
+++ b/lib/day3/command.dart
@@ -27,6 +27,7 @@ class Day3Command extends Command {
       print(
         "Expected 1 positional arguments, found ${argResults!.rest.length}",
       );
+      exit(1);
     }
     var filePath = argResults!.rest[0];
 
diff --git a/lib/day4/command.dart b/lib/day4/command.dart
new file mode 100644
index 0000000..69afc21
--- /dev/null
+++ b/lib/day4/command.dart
@@ -0,0 +1,36 @@
+import "dart:convert";
+import "dart:io";
+
+import "package:args/command_runner.dart";
+
+class Day4Command extends Command {
+  // The [name] and [description] properties must be defined by every
+  // subclass.
+  @override
+  final name = "day4";
+
+  @override
+  final description = "Run Advent of Code 2025 Day 3";
+
+  Day4Command() {
+    // we can add command specific arguments here.
+    // [argParser] is automatically created by the parent class.
+  }
+
+  // [run] may also return a Future.
+  @override
+  Future<void> run() async {
+    // [argResults] is set before [run()] is called and contains the flags/options
+    // passed to this command.
+
+    if (argResults!.rest.length != 1) {
+      print(
+        "Expected 1 positional arguments, found ${argResults!.rest.length}",
+      );
+      exit(1);
+    }
+    var filePath = argResults!.rest[0];
+
+    print("Parsing file: $filePath");
+  }
+}