Thank you for all of your help! I finally got it working! However, I have another question. I'm not very familiar with lookarounds but I think that they would increase the throughput of my program exponentially!

I would like to use a lookahead (and/or lookbehind, I don't really know the difference..) assertion after matching a pattern (from a list of patterns) at either the beginning or end of the string. The lookaround would search for an adjacent pattern that is also from the list (NOTE: order does not matter!). If there is no known adjacent pattern, then remove the 6 characters preceding or following the pattern (as we have done already); if there is a pattern, proceed with some other instruction (of which is not relevant). The following is pseudocode to help explain:

$pattern_A = "123";
$pattern_b = "456";

$string_1 = "1234567890";
$string_2 = "1236547890";

# Then apply regex/lookaround to search for adjacent pattern

if($adjacent_pattern == false){
     remove_pattern_and_six_following_characters;
     print("string_*");
}
else{
     do_something_else;
     print("string_*");
}
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The output for $string_1 would be:
string_1 = 1234567890
as it had an adjacent known pattern, the program performed some other function.

The output for $string_2 would be:
string_2 = 0
as it did not have an adjacent known pattern, the pattern that was matched and the following 6 characters were removed.

Let me know if you need to know anything else!! Thank you very much!!