Very simple to implement, actually -

%magichash;
&magic(\%magichash, '/path/to/file/fn');
print $magichash{'/path/to/file/fn'};

sub magic {
    my $handle;
    if (open($handle, $_[1])) {
        $_[0]->{$_[1]} = join('', <$handle>);
        close($handle);
        return 1;
    }
}
[download]

Note that the sub also returns a bool response, so you can tell if it successfully loaded the file or not.