Dear Monks,

I have a problem I am trying to solve with regular expressions. I want to return all locations of an array of patterns inside a string. I also only want the patterns to match at locations which are a multiple of 3. For example, so far I have the following.

my $string="AAABBBCCCCDDDEEEFFFGGGHHHIII";
my @patterns=('BBB','DDD');
my @index;
foreach(@patterns){
while($string=~m/([A-Z]{3})+?$_/g){
push(@index,$-[2]);
pos($string)=$-[2];
}
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The problem with this is that it matches the first pattern correctly, but it will also match 'CCCDDD' in the second loop because I cannot/dont know how to anchor the pattern to start at a specific location.

To be clear, I only want the patterns in the array to match if there are a number of characters evenly divisible by three before it.

Is there a good way to do this?