Something

#!/usr/bin/perl
#

$string = $ARGV[0];

$length = length($string);

for($i = $length; $i >= 0; $i--) {
    $c = substr($string, $i, 1);

    if($c eq "i") {
        print "Last char ($c) at byte $i\n";
        exit;
    }
}


print "\n";