--- /dev/null
+//===-- runtime/command.cpp -----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "command.h"
+#include "environment.h"
+
+namespace Fortran::runtime {
+CppTypeFor<TypeCategory::Integer, 4> RTNAME(ArgumentCount)() {
+ int argc{executionEnvironment.argc};
+ if (argc > 1) {
+ // C counts the command name as one of the arguments, but Fortran doesn't.
+ return argc - 1;
+ }
+ return 0;
+}
+} // namespace Fortran::runtime
--- /dev/null
+//===-- flang/unittests/RuntimeGTest/CommandTest.cpp ----------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "../../runtime/command.h"
+#include "gtest/gtest.h"
+#include "../../runtime/descriptor.h"
+#include "../../runtime/main.h"
+
+using namespace Fortran::runtime;
+
+TEST(ArgumentCount, ZeroArguments) {
+ const char *argv[]{"aProgram"};
+ RTNAME(ProgramStart)(1, argv, {});
+ EXPECT_EQ(0, RTNAME(ArgumentCount)());
+}
+
+TEST(ArgumentCount, OneArgument) {
+ const char *argv[]{"aProgram", "anArgument"};
+ RTNAME(ProgramStart)(2, argv, {});
+ EXPECT_EQ(1, RTNAME(ArgumentCount)());
+}
+
+TEST(ArgumentCount, SeveralArguments) {
+ const char *argv[]{"aProgram", "arg1", "arg2", "arg3", "arg4"};
+ RTNAME(ProgramStart)(5, argv, {});
+ EXPECT_EQ(4, RTNAME(ArgumentCount)());
+}