void verify_filename(const char *prefix, const char *arg)
{
	const char *name;
	struct stat st;

	if (*arg == '-')
		die("bad flag '%s' used after filename", arg);
	name = prefix ? prefix_filename(prefix, strlen(prefix), arg) : arg;
	if (!lstat(name, &st))
		return;
	if (errno == ENOENT)
		die("ambiguous argument '%s': unknown revision or path not in the working tree.\n"
		    "Use '--' to separate paths from revisions", arg);
	die("'%s': %s", arg, strerror(errno));
}
Unknown