use strict;
use warnings;

my @midWords = qw(stop start finish);
my %sentences =
    (
    1 => "Start starts the start sentence.",
    2 => "This is a sentence in the middle.",
    3 => "This is not the start or the finish, nor even a good place to stop.",
    4 => "This is the finish and a good place to stop."
    );
    
my %testWords;
@testWords{@midWords} = (0);

foreach my $sentence (values %sentences){
    for (split /\W/, $sentence) {
        ++$testWords{lc $_} if exists $testWords{lc $_};
    }
}

print join "\n", map {"$_ => $testWords{$_}"} sort keys %testWords;