Quick subroutine to return the number of vowels in a string. returns -1 if the string is not an ascii string.

asciiVowelCount.pl

sub asciiVowelCount {

  my $str = shift;

  # return error since this is not ascii character set
  return -1 if $str =~ /[^[:ascii:]]/;

  my $count = 0;

  # Loop over each chracter in $str and increment counter if it is a vowel
  for my $char (split //, $str) {
    $count++ if $char =~ m/[aiueo]/;
  }

  return $count;
}