This actually uses index, so it should run faster than regex based versions. Benchmarking is left as an exercise for the more interested. :)

sub index_a {
  my( $txt, $search ) = @_;
  my @ret;
  my $ind = 0;
  my $cur = 0;

  while( ($cur = index( $txt, $search, $ind )) != -1 ) {
    push @ret, $cur;
    $ind = $cur + 1;
  }

  return @ret;
}
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