feat: return exit code

src/command.c

@@ -6,12 +6,14 @@
 #include <unistd.h>
 
 unsigned char invoke(struct Args args) {
+  int status;
+
   pid_t child = fork();
   if (child == 0) {
     execvp(args.argv[0], args.argv);
     exit(errno);
   }
-  waitpid(child, NULL, 0);
+  wait(&status);
 
-  return 0;
+  return WEXITSTATUS(status);
 }

src/main.c

@@ -7,19 +7,20 @@
 
 int main() {
   char *input_line;
+  unsigned char exit_code = 0;
 
   while (1) {
     printf("$ ");
     input_line = read_a_line(stdin);
     if (input_line == NULL) {
-      return 0;
+      return exit_code;
     }
 
     struct Args args = parse(input_line);
     free(input_line);
 
     if (args.argc > 0) {
-      invoke(args);
+      exit_code = invoke(args);
     }
 
     {