>perl -wMstrict -le
"my $dna = 'xxpecbcbccrlxxxPeeeerlxxpLxxxPeRLxx';
 ;;
 my $perl = qr{ [Pp] [^x]* [Ll] }xms;
 ;;
 my @matches = $dna =~ m{ $perl }xmsg;
 printf qq{'$_' } for @matches;
"
'pecbcbccrl' 'Peeeerl' 'pL' 'PeRL'