my $phrase = 'There once was a doggy in the window. I went into the store and inquired about the price, the doggy was too nice to ever think twice, so now I have a doggy to care for.';

my %vowels;
while ($phrase =~ /([aeiou])/gi) {
    $vowels{lc $1}++;
}

use YAML;
print Dump \%vowels;

__END__


the output would look like

---
a: 8
e: 17
i: 11
o: 15
u: 2