# To find all occurance of "bc" preceeded by 3 letters, and followed by 2 letters.
$str = "aaabcabcdebcaabebcb";
while($str =~ /(\w{3}bc\w{2})/g){
    print "$-[1],$+[1],$1\n";
}
__OUTPUT__
0,7,aaabcab
7,14,cdebcaa

##</code><code>##

__OUTPUT__
0,6,aaabcab
3,9,bcabcde
7,13,cdebcaa