grep /^[a-z]+$/, (join(" ",<>)=~/(\w+)/g)

##</code><code>##

print "$_\n" for sort keys %{{
 map {$_, 1} grep /^[a-z]+$/, (join(" ",<>)=~/(\w+)/g)
}};

##</code><code>##

print "$_\n" for sort keys %{{
 map {$_, 1} join(" ",<>)=~/\b[a-z]+\b/g
}};

##</code><code>##

my %hash;
$hash{$_}++ for
 join(" ",<>)=~/\b[a-z]+\b/g;
print "$_\n" for sort keys %hash;