Added main file.

shell_main.cpp

@@ -0,0 +1,79 @@
+#include <iostream>
+#include <string>
+#include <sstream>
+
+using namespace std;
+
+int main()
+{
+  string input;
+
+  while (true)
+  {
+    cout << "$ ";
+    getline(cin, input);
+
+    istringstream iss(input);
+    string command;
+    iss >> command;
+
+    if (command == "exit")
+    {
+      exit(1);
+    }
+    else if (command == "print")
+    {
+      // TODO: Print the current PID
+    }
+    else if (command == "help")
+    {
+      // TODO: Print help information
+    }
+    else
+    {
+      // Execute an external command
+      pid_t pid = fork();
+
+      if (pid == 0)
+      {
+        // Child process
+        // Convert the command string to a C string
+        char *cmd = const_cast<char *>(command.c_str());
+
+        // Convert the arguments to an array of C strings
+        int i = 0;
+        char *args[100];
+
+        args[i++] = cmd;
+
+        string arg;
+        while (iss >> arg && i < 100)
+        {
+          args[i++] = const_cast<char *>(arg.c_str());
+        }
+
+        args[i] = nullptr;
+
+        // Execute the command
+        execvp(cmd, args);
+
+        // If execvp returns, it must have failed
+        cout << "Command not found: " << command << endl;
+        exit(EXIT_FAILURE);
+      }
+      else if (pid > 0)
+      {
+        // Parent process
+        int status;
+        waitpid(pid, &status, 0);
+      }
+      else
+      {
+        // Failed to fork
+        cout << "Failed to fork" << endl;
+      }
+    }
+  }
+
+  return 0;
+}