diff --git a/bin/main.cpp b/bin/main.cpp
index 4c6fdf5..3a1c5fe 100644
--- a/bin/main.cpp
+++ b/bin/main.cpp
@@ -181,5 +181,8 @@ int main(int argc, char *argv[])
 
   {// ex: utils::exec
     hack::log()(hack::utils::exec("ls"));
+    hack::log()(hack::utils::exec("pwd"));
+    auto t = hack::utils::exec("pwd");
+    hack::log::type_trace(t);
   }
 }
diff --git a/src/iterators/sequence_ostream_iterator.hpp b/src/iterators/sequence_ostream_iterator.hpp
index 6c2a362..5de87b1 100644
--- a/src/iterators/sequence_ostream_iterator.hpp
+++ b/src/iterators/sequence_ostream_iterator.hpp
@@ -12,7 +12,7 @@ namespace hack::iterators
 
     private:
       std::basic_ostream<char, traits>* os_;
-      const std::string devider_ = ", ";
+      std::string devider_ = ", ";
       std::size_t size_;
 
     public:
diff --git a/src/logger/logger.cpp b/src/logger/logger.cpp
index 520f4df..abcb4fe 100644
--- a/src/logger/logger.cpp
+++ b/src/logger/logger.cpp
@@ -5,17 +5,17 @@ namespace hack
   std::string log::devider = " ";
   int log::count = 0;
 
-  log::log(const std::string devider_, std::experimental::source_location location_) : location { location_ }
+  log::log(std::string devider_, std::experimental::source_location location_) : location { location_ }
   {
     this->devider = devider_;
   }
 
-  warn::warn(const std::string devider_, std::experimental::source_location location_) : location { location_ }
+  warn::warn(std::string devider_, std::experimental::source_location location_) : location { location_ }
   {
     this->devider = devider_;
   }
 
-  error::error(const std::string devider_, std::experimental::source_location location_) : location { location_ }
+  error::error(std::string devider_, std::experimental::source_location location_) : location { location_ }
   {
     this->devider = devider_;
   }
diff --git a/src/logger/logger.hpp b/src/logger/logger.hpp
index b6a5c1a..eae2fc1 100644
--- a/src/logger/logger.hpp
+++ b/src/logger/logger.hpp
@@ -24,7 +24,7 @@ namespace hack
   class log
   {
     public:
-      log(const std::string devider_ = ", ", std::experimental::source_location location_ = std::experimental::source_location::current()); 
+      log(std::string devider_ = ", ", std::experimental::source_location location_ = std::experimental::source_location::current()); 
       log(log&) = delete;
       log(log&&) = delete;
 
@@ -135,7 +135,7 @@ namespace hack
   class warn : public log
   {
     public:
-      warn(const std::string devider_ = ", ", std::experimental::source_location location_ = std::experimental::source_location::current());
+      warn(std::string devider_ = ", ", std::experimental::source_location location_ = std::experimental::source_location::current());
       warn(log&) = delete;
       warn(log&&) = delete;
 
@@ -162,7 +162,7 @@ namespace hack
   class error : public log
   {
     public:
-      error(const std::string devider_ = ", ", std::experimental::source_location location_ = std::experimental::source_location::current()); 
+      error(std::string devider_ = ", ", std::experimental::source_location location_ = std::experimental::source_location::current()); 
       error(log&) = delete;
       error(log&&) = delete;
 
diff --git a/src/string/string_concat_helper.hpp b/src/string/string_concat_helper.hpp
index 73b0748..d79aa8a 100644
--- a/src/string/string_concat_helper.hpp
+++ b/src/string/string_concat_helper.hpp
@@ -70,7 +70,7 @@ namespace hack::string
   };
 
   template <typename Stream, typename... Strings>
-  Stream& operator<<(Stream& stream, const string_concat_helper<Strings...> strings)
+  Stream& operator<<(Stream& stream, string_concat_helper<Strings...> strings)
   {
     return stream << static_cast<std::string>(strings);
   }
diff --git a/src/utils/utils.hpp b/src/utils/utils.hpp
index c2b53d6..ecc5728 100644
--- a/src/utils/utils.hpp
+++ b/src/utils/utils.hpp
@@ -48,13 +48,13 @@ namespace hack::utils
 
   inline std::string exec(const char* cmd) 
   {
-    std::array<char, 128> buffer;
     std::string result;
+    std::array<char, 128> buffer;
     std::unique_ptr<FILE, decltype(&pclose)> pipe(popen(cmd, "r"), pclose);
 
     if (!pipe) 
     {
-      throw std::runtime_error("popen() failed!");
+      throw std::runtime_error("bash cmd failed");
     }
     
     while (fgets(buffer.data(), buffer.size(), pipe.get()) != nullptr)