If you use a regular expression you need to be aware that open and close square brackets are metacharacters so need to be escaped to match literally. You can use regex captures and a global match to pull out the items within the brackets.

use strict;
use warnings;

my $string = q{hereiam[[[one]]][[[two]]][[[three]]]wwhat};
my @strings = $string =~ m{\[+([^\]]*])\]+}g;

print qq{@strings\n};
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This produces

one two three
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To make your posts easier to read you should surround code with <code> and </code> tags.

I hope this is of use.

Cheers,

JohnGG