>perl -wMstrict -le
"my @strs = (
   'Servername FOO',
   'fine Servername FOO yyy',
   'no Servername FOO zzz',
   'cool Servername BAR',
   'nyet Servername BAR vvv',
   'Servername BOFF',
   'ok Servername BOFF yyy',
   'no Servername BOFF zzz',
   );
 ;;
 my @names = qw(FOO BAR);
 my @avoid = qw(no nyet);
 ;;
 my $find = join '|', @names;
    $find = qr{ Servername \s+ (?: $find) }xms;
 ;;
 my $not_before = join '|', @avoid;
    $not_before = qr{ (?: $not_before) \s+ Servername  }xms;
    $not_before = qr{ (?: $not_before (*SKIP)(*FAIL))? }xms;
 ;;
 for my $s (@strs) {
   print qq{'$s'} if $s =~ m{ $not_before $find }xms;
   }
"
'Servername FOO'
'fine Servername FOO yyy'
'cool Servername BAR'