diff --git a/src/mfm_dup.cpp b/src/mfm_dup.cpp
new file mode 100644
index 00000000..c66ba790
--- /dev/null
+++ b/src/mfm_dup.cpp
@@ -0,0 +1,48 @@
+#include "mfm_options.hpp"
+
+#include <filesystem>
+
+#include "fmt/core.h"
+
+namespace fs = std::filesystem;
+
+namespace mfm
+{
+  void dup(const Opts::Dup &opts);
+}
+
+void
+mfm::dup(const Opts::Dup &opts_)
+{
+  if(fs::is_regular_file(opts_.path))
+    {
+    }
+  else if(fs::is_directory(opts_.path))
+    {
+      auto dir_opts = (fs::directory_options::follow_directory_symlink |
+                       fs::directory_options::skip_permission_denied);
+
+      for(const fs::directory_entry &de :
+            fs::recursive_directory_iterator(opts_.path,dir_opts))
+        {
+          if(!de.is_directory())
+            continue;
+
+          std::error_code ec;
+          auto filepath = de.path() / ".dup_2";
+          if(!fs::exists(filepath,ec))
+            continue;
+
+          fmt::println("{}:",filepath.string());
+          for(const fs::directory_entry &de :
+                fs::directory_iterator(de.path()))
+            {
+              fmt::println("{}",de.path().string());
+            }
+        }
+    }
+  else
+    {
+      throw std::runtime_error("invalid file type");
+    }
+}