Here's an illustration of what Eimi Metamorphoumai described. 
sub test {
   my ($sentence, $re) = @_;

   print("Sentence: $sentence\n");
   print("Regexp:   $re\n");

   if ($sentence =~ /($re)/) {
      printf("Matched %d characters (%s) at pos %d\n",
         length($1), $1, $-[1]);
   } else {
      print("No match\n");
   }

   print("\n");
}

test("1234",    qr/\d*/);  # Matched 4 characters (1234) at pos 0
test("abc1234", qr/\d*/);  # Matched 0 characters () at pos 0
test("abc",     qr/\d*/);  # Matched 0 characters () at pos 0

test("1234",    qr/\d+/);  # Matched 4 characters (1234) at pos 0
test("abc1234", qr/\d+/);  # Matched 4 characters (1234) at pos 3 (*1)
test("abc",     qr/\d+/);  # No match (*2)

[download]

*1 - Since it failed at positions 0, 1 and 2.
*2 - Since it failed at all positions.

Update: Combined the code and the output to condense the node and improve readability.

In reply to Re^2: question about the star(*) quantifier by ikegami
in thread question about the star(*) quantifier by snowsky

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