diff --git a/lib/src/Startup.cpp b/lib/src/Startup.cpp
index 81df39a..fc5721c 100644
--- a/lib/src/Startup.cpp
+++ b/lib/src/Startup.cpp
@@ -6,18 +6,62 @@
 #include <memory>
 #include <fstream>
 #include <utility>
+#include <unistd.h>
 
 #define DOCTEST_CONFIG_IMPLEMENT
 #include <doctest.h>
 
 auto main(int argc, char ** argv) -> int
 {
-  if (std::getenv("DOCTEST")) {
-      return doctest::Context{argc, argv}.run();
-  }
+  bool run_tests {};
+  char const* in_name {};
+  char const* out_name {};
 
   try {
-    Main(std::cin, std::cout);
+    int ch;
+    while ((ch = getopt(argc, argv, ":hi:o:t")) != -1) {
+      switch (ch) {
+        case 'i': in_name = optarg; break;
+        case 'o': out_name = optarg; break;
+        case 't': run_tests = true; break;
+        case ':':
+          std::cerr << "Missing argument to -" << char(optopt) << std::endl;
+          return 1;
+        case 'h':
+          std::cerr << "Usage: " << argv[0] << " [-i INPUT] [-o OUTPUT] [-t]" << std::endl;
+          return 0;
+        case '?':
+        default:
+          std::cerr << "Unknown flag -" << char(optopt) << std::endl;
+          return 1;
+      }
+    }
+
+    if (run_tests) {
+      return doctest::Context{argc, argv}.run();
+    }
+
+    std::unique_ptr<std::istream, void(*)(std::istream*)> in
+      {in_name
+        ? decltype(in){new std::ifstream{in_name}, [](auto p) { delete p; }}
+        : decltype(in){&std::cin, [](auto){}}};
+
+    if (in->fail()) {
+      std::cerr << "Bad input file" << std::endl;
+      return 1;
+    }
+
+    std::unique_ptr<std::ostream, void(*)(std::ostream*)> out
+      {out_name
+        ? decltype(out){new std::ofstream{out_name}, [](auto p) { delete p; }}
+        : decltype(out){&std::cout, [](auto){}}};
+
+    if (out->fail()) {
+      std::cerr << "Bad output file" << std::endl;
+      return 1;
+    }
+
+    Main(*in, *out);
   } catch (std::exception const& e) {
     std::cerr << "Program failed: " << e.what() << std::endl;
     return 1;