allow help to be printed

src/main.cpp

@@ -53,14 +53,19 @@ static void enforce_infinite_rlimit() {
         "\"ulimit -l 8192\" to fix the problem" << std::endl;
 }
 
-int main(int argc, char *argv[])
+bool is_root()
 {
   if (geteuid() != 0)
   {
     std::cerr << "ERROR: bpftrace currently only supports running as the root user." << std::endl;
-    exit(0);
+    return false;
   }
+  else
+    return true;
+}
 
+int main(int argc, char *argv[])
+{
   int err;
   Driver driver;
   char *pid_str = NULL;
@@ -107,6 +112,9 @@ int main(int argc, char *argv[])
   // Listing probes
   if (listing)
   {
+    if (!is_root())
+      return 1;
+
     if (optind == argc-1)
       list_probes(argv[optind]);
     else if (optind == argc)
@@ -140,6 +148,9 @@ int main(int argc, char *argv[])
     err = driver.parse_str(script);
   }
 
+  if (!is_root())
+    return 1;
+
   if (err)
     return err;