Use a backreference.

if (!$flag && /($octet)/){
   print "$1\n";
}
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From Camel 3, p. 41:
A pair of parenthesis around a part of a regular expression causes whatever was matched by that part to be remembered for later use.

$1 is the match from the first set of parenthesis in your regexp, $2 the second, and so on.