When I have a moment I want to check to see if this is a faster way of finding the 50k-th "!":

if(
  $string =~ m/(?:[^!]*!){49999}[^!]*!/;
) {
  print $+[0] + 1, "\n" # Updated.
}
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It *could* be, because it keeps all the work inside of Perl's internals. If Perl had a native function that said, "find_nth($string, '!')", it would beat any regexp solution, but it doesn't (at least not as a built-in).

Update: "Quantifier in {,} bigger than 32766 in regex; marked by <-- HERE in m/(?:[^!]*!){ <-- HERE 49999}[^!]*!/ at mytest10.pl line 27." (I forgot about that.)

Update 2: Assuming we're only dealing with ASCII, this is trivial using Inline::C. Walking the string and making the change up to 50k times will be trivial, and fast. If I get around to it I'll post an example.