diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0c9c29f..496b481 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -3,7 +3,8 @@ project(md5sum LANGUAGES CXX)
 
 # ------------------------------------------------------------------------------------ #
 
-option(MD5_SHARED_LIB "Built as a dynamic library." OFF)
+option(MD5_BUILD_DEMO "Build md5 demo binary." OFF)
+option(MD5_SHARED_LIB "Build as a dynamic library." OFF)
 option(MD5_ENABLE_LTO "Enable LTO optimization of the library." ON)
 option(MD5_ENABLE_TESTING "Enable testing of the md5sum library." OFF)
 option(MD5_ENABLE_BENCHMARK "Enable benchmark of the md5sum library." OFF)
@@ -44,15 +45,22 @@ else()
     add_library(md5sum SHARED ${MD5_SRC})
     target_compile_options(md5sum PRIVATE -fvisibility=hidden)
 endif()
-target_include_directories(md5sum PUBLIC src/)
 
 set(MD5_COMPILE_OPTIONS -fno-rtti -fno-exceptions)
 target_compile_options(md5sum PRIVATE ${MD5_COMPILE_OPTIONS})
-
+target_include_directories(md5sum PUBLIC src/)
 add_library(md5sum::md5sum ALIAS md5sum)
 
 # ------------------------------------------------------------------------------------ #
 
+if (MD5_BUILD_DEMO)
+    add_executable(md5_demo demo.cc)
+    target_link_libraries(md5_demo PRIVATE md5sum)
+    target_compile_options(md5_demo PRIVATE ${MD5_COMPILE_OPTIONS})
+endif()
+
+# ------------------------------------------------------------------------------------ #
+
 include(third_party/ThirdParty.cmake)
 
 if (MD5_ENABLE_TESTING)
diff --git a/demo.cc b/demo.cc
new file mode 100644
index 0000000..8d04059
--- /dev/null
+++ b/demo.cc
@@ -0,0 +1,80 @@
+#include "md5.h"
+#include <iostream>
+#include <optional>
+
+using md5::MD5;
+
+#if not __linux__
+std::optional<std::string> hash_file(const std::string_view &file_name) {
+    auto *fp = std::fopen(file_name.data(), "rb");
+    if (!fp) {
+        std::perror("File open failed");
+        return std::nullopt;
+    }
+
+    MD5 md5;
+    size_t len;
+    char buffer[BUFSIZ];
+    while ((len = std::fread(buffer, sizeof(char), BUFSIZ, fp)) > 0) {
+        md5.Update(buffer, len);
+    }
+    if (std::ferror(fp)) {
+        std::perror("File read failed");
+        std::fclose(fp);
+        return std::nullopt;
+    }
+    std::fclose(fp);
+    return md5.Final().Digest();
+}
+
+#else
+
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+
+std::optional<std::string> hash_file(const std::string_view &file_name) {
+    auto fd = open(file_name.data(), O_RDONLY);
+    if (fd < 0) {
+        std::perror("File open failed");
+        return std::nullopt;
+    }
+
+    struct stat st {};
+    fstat(fd, &st);
+    auto file_size = st.st_size;
+
+    auto ptr = mmap(nullptr, file_size, PROT_READ, MAP_PRIVATE, fd, 0);
+    close(fd);
+    if (ptr == MAP_FAILED) {
+        std::perror("File mapping failed");
+        return std::nullopt;
+    }
+    auto result = MD5::Hash(ptr, file_size);
+    if (munmap(ptr, file_size)) {
+        std::perror("File unmapping failed");
+    }
+    return result;
+}
+#endif
+
+constexpr auto NO_ERROR = 0;
+constexpr auto ARG_ERROR = 1;
+constexpr auto FILE_ERROR = 2;
+
+int main(int argc, char *argv[]) {
+    if (argc == 1) {
+        std::cout << "Usage: " << argv[0] << " [FILE]" << std::endl;
+        return NO_ERROR;
+    } else if (argc != 2) {
+        std::cout << "Invalid MD5 arguments" << std::endl;
+        return ARG_ERROR;
+    }
+
+    if (auto result = hash_file(argv[1]); result.has_value()) {
+        std::cout << result.value() << std::endl;
+        return NO_ERROR;
+    }
+    return FILE_ERROR;
+}