#!/usr/bin/perl

my $str = "123.0456.0789.0-WHOOPS";
my $sub = ".0";

print "str before = $str\n";
$str = rm_nth($str,$sub,2);
print "str  after = $str\n";

sub rm_nth {
   my ($str,$sub,$n) = @_;  $n = 1 if $n < 1;
   my $p = -1;

   while ($n--) {
      $p = index($str,$sub,$p+1);
      return $str if $p < 0;
   }
   substr($str,$p,length($sub)) = "";
   return $str;
}