Something

warn("Unexpected number of keys ($numkeys) in $meetingFile, expected 3, warning "); 
print("Checking if we have the right keys anyway...");
@neededSections = ('aantalhuisjes','aantalinvalidenhuisjes','personenperhuis');
foreach $section (@neededSections) {
    defined %meeting['$section'] || die("Nope, we're missing a section ($section). Too bad. Stopped");
}