Hide shell functions from _G using upvalues on the main chunk

Store __command, __interactive, __getenv, __setenv as upvalues
populated by lua_load() from the registry, keeping them invisible
to user code while accessible to the parser's codegen.

linit.c

@@ -43,41 +43,21 @@ static const luaL_Reg stdlibs[] = {
 };
 
 
-static int luaB_getenv (lua_State *L) {
-  const char *name = luaL_checkstring(L, 1);
-  const char *val = getenv(name);
-  if (val == NULL)
-    lua_pushnil(L);
-  else
-    lua_pushstring(L, val);
-  return 1;
-}
-
-
-static int luaB_setenv (lua_State *L) {
-  const char *name = luaL_checkstring(L, 1);
-  if (lua_isnoneornil(L, 2))
-    unsetenv(name);
-  else {
-    const char *val = luaL_tolstring(L, 2, NULL);
-    setenv(name, val, 1);
-  }
-  return 0;
-}
-
-
 /*
-** Register shell built-in globals (called after standard libraries).
+** Store shell functions in a registry table at LUA_RIDX_LUSH.
+** These are populated as upvalues on the main chunk by lua_load().
 */
 static void opencommand (lua_State *L) {
-  lua_pushcfunction(L, luaB_command);
-  lua_setglobal(L, "__command");
-  lua_pushcfunction(L, luaB_interactive);
-  lua_setglobal(L, "__interactive");
-  lua_pushcfunction(L, luaB_getenv);
-  lua_setglobal(L, "__getenv");
-  lua_pushcfunction(L, luaB_setenv);
-  lua_setglobal(L, "__setenv");
+  lua_createtable(L, 0, 5);
+  lua_pushcfunction(L, lushCmd_command);
+  lua_setfield(L, -2, "command");
+  lua_pushcfunction(L, lushCmd_interactive);
+  lua_setfield(L, -2, "interactive");
+  lua_pushcfunction(L, lushCmd_getenv);
+  lua_setfield(L, -2, "getenv");
+  lua_pushcfunction(L, lushCmd_setenv);
+  lua_setfield(L, -2, "setenv");
+  lua_rawseti(L, LUA_REGISTRYINDEX, LUA_RIDX_LUSH);
 }