def _get_picard_cmd(self, command, memscale=None):
        """Retrieve the base Picard command, handling both shell scripts and directory of jars.
        """
        resources = config_utils.get_resources("picard", self._config)
        if memscale:
            jvm_opts = get_picard_opts(self._config, memscale=memscale)
        elif resources.get("jvm_opts"):
            jvm_opts = resources.get("jvm_opts")
        else:
            jvm_opts = self._jvm_opts
        if os.path.isdir(self._picard_ref):
            dist_file = self._get_jar(command)
            return ["java"] + jvm_opts + get_default_jvm_opts() + ["-jar", dist_file]
        else:
            # XXX Cannot currently set JVM opts with picard-tools script
            return [self._picard_ref, command]
Retrieve the base Picard command, handling both shell scripts and directory of jars.