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while (my ($word) = (lc $word) =~ /[a-z]{2,}/g) {

my %hash;
while (my $line = <STDIN>) {
...
    }
}
print "$_\n" for sort keys %hash;

while (my $line = <STDIN>) {
    $hash{lc $_}++ for $line =~ m/\b([a-zA-Z]{2,4})\b/g;
}
#or
do { $hash{lc $_}++ for m/\b([a-zA-Z]{2,4})\b/g } for <STDIN>;

while (my $line = <STDIN>) {
    $hash{lc $_}++ for $line =~ m/([a-zA-Z]{2,})/g;
}
delete $hash{$_} for grep /(\w)\1{4}/, keys %hash;