while ($s =~ /abc/g) {
   print "found abc at $-[0]\n";
}
##</code><code>##

while ($s =~ /aa/g) {
   print "found aa at $-[0]\n";
}
##</code><code>##

  found aa at 1
  found aa at 3

##</code><code>##

while ($s =~ /aa/g) {
   print "found aa at $-[0]\n";
   pos($s) = $-[0] + 1;
}