Because the string 'doghouse' is not found in the string 'dog', and because you aren't returning the strings, but rather printing them ...

(While I'm at it ... don't use $a and $b for other than sorting. They're "special".)

This would return "found":

$A = 'dog';
$B = 'doghouse';
if($B =~ /$A/){
  return "found";
}
else{
  return "not found!";
}
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