rot13
rot13(Fortbuf, (sp - Fortbuf));
static void rot13(char *line, int len);
rot13(line, 0);
rot13(pat, 0);
PUFFSOP_SET(pops, rot13, node, readdir);
PUFFSOP_SET(pops, rot13, node, read);
PUFFSOP_SET(pops, rot13, node, write);
PUFFSOP_PROTOS(rot13)
char rot13 = ch >= 'a' && ch <= 'm' ? ch + 13
snprintf(expected, sizeof(expected), "%#x<%c>", ch, rot13));