expandm
if (vasprintf(&buf, expandm(fmt, NULL, &bufx), ap) == -1)
printf("%s\n", expandm(argc > 1 ? argv[1] : "Message %%m=%m: %%%m%%",
const char * __attribute__((__format_arg__(1))) expandm(const char *,
vwarnx(expandm(fmt, "", &buf), ap);