Further to ikegami's point, here's an illustration of the way the /g modifier causes the regex engine to interact with the position offset (if that's the right term) of a string as returned by pos.

>perl -wMstrict -le
"my $s = 'oneone';
 my $regex = qr/one/;
 ;;
 for (1 .. 6) {
   if ($s =~ /$regex/g) {
     printf qq{matches '$&' at %d, pos at %d \n}, $-[0], pos $s;
     }
   else {
     print 'no match';
     }
   }
"
matches 'one' at 0, pos at 3
matches 'one' at 3, pos at 6
no match
matches 'one' at 0, pos at 3
matches 'one' at 3, pos at 6
no match
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