Use zero-width lookahead and lookbehind: 

$str = "aaabcabcdebcaabebcb";
while($str =~ /(?<=\w{3})(bc)(?=\w{2})/g){
    print "$-[1],$+[1],$1\n";
}

[download]
update: As my esteemed fellow monk Tankalus reminds me, you'll need to adjust your mechanism for retrieving the exact characters you require.

duff

In reply to Re: Regex: continuous matching positions by duff
in thread Regex: continuous matching positions by theshz

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