shell: fix more unused warnings

src/shell.cpp

@@ -84,8 +84,14 @@ std::string Shell::exec(std::string cmd) {
     return readOutput();
 }
 
+void Shell::writeCommand(const std::string& command) {
+    if (write(to_shell[1], command.c_str(), command.length()) == -1)
+    SPDLOG_ERROR("Failed exit shell");
+}
+
 Shell::~Shell() {
-    write(to_shell[1], "exit\n", 5);
+    if (write(to_shell[1], "exit\n", 5) == -1)
+        SPDLOG_ERROR("Failed exit shell");
     close(to_shell[1]);
     close(from_shell[0]);
     waitpid(shell_pid, nullptr, 0);

src/shell.h

@@ -22,10 +22,7 @@ private:
     }
 #endif
 
-    void writeCommand(const std::string& command) {
-        write(to_shell[1], command.c_str(), command.length());
-    }
-
+    void writeCommand(const std::string& command);
     std::string readOutput();
 
 public: