parse_line($string);ipv6_flowlabel.sh runs ipv6_flowlabel_mgr, whose __expect() macro prints the status first, e.g.:
# [OK] flowlabel_get(fd, 1, 255, 0)On failure it calls error(), which aborts the process after printing '[ERR] <expr> (line N)', optionally prefixed by the program name. Lines that do not match this format are returned unchanged.