use Regexp::Common qw /balanced/;

$r = qr/$RE{balanced}{-begin => "<%"}{-end => "%>"}/;

@list = ("aa<% <% %>bb", "aa<% %> <% %>bb", "aa<% <% %> %>bb", "aa<% >% %>bb");

for (@list){
    /($r)/;
    print "$` \t| $1 \t| $'\n";
}