pos($titles) = 0;
[download]

For example,

my $titles = 'abcde';

for (1..2) {
   pos($titles) = 0;
   for (1..3) {
      $titles =~ /./g or die;
      print(substr($titles, pos($titles)-1, 1), "\n");
   }
}
[download]

prints

a
b
c
a
b
c
[download]

You should probably be using index, though.

Update: Added example.