$needle = "a";
$haystack =~ /\Q$needle\E/i;
$index = $-[0];

##</code><code>##

$needle = "a";
$haystack =~ /\Q$needle\E/i;
$index = pos($haystack)-length($needle);

##</code><code>##

$needle = "a";
$haystack =~ /\Q$needle\E/i;
$index = length($`);