$ perl -E '
    my @strings = qw{
        no_data_string
        /DATA_String/
        X/DATA_String/
        /some/path/to/DATA_String/
    };

    say "-" x 40;

    for my $string (@strings) {
        say "\$string[$string]";

        for my $pos (qw{0 -1}) {
            say "\$pos[$pos]";

            if (index($string, "/DATA_String/") > $pos) {
                say "index() TRUE";
            }
            else {
                say "index() FALSE";
            }
        }

        say "-" x 40;
    }
'