for (p = opt->header_list; p; p = p->next) {
if (p->token != GREP_PATTERN_HEAD)
die("bug: a non-header pattern in grep header list.");
for (p = opt->header_list; p; p = p->next) {
if (p->token != GREP_PATTERN_HEAD)
die("bug: a non-header pattern in grep header list.");