I would just use a regular expression:

if ($line =~ m/([\0-\x8\xb-\x1f\x7e-\xff])/) {
  print "$line contains illegal character (ord: ", ord($1), ")\n";
}
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The reason why your code isn't working is because instead of:

  @character=split /\.*/;
  while (@character){
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you really want:

  @character=split //; # split $_ into single characters
  while (@character){
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With the original split call, when there's a dot at the beginning of the line the first element of @character is the empty string.