FileContentCounter.php

<?php

class FileContentCounter
{
    private $file;

    public function __construct($file)
    {
        $this->file = $file;
    }

    public function getWordsCount()
    {
        $text = $this->getFileContent();

        return str_word_count($text);
    }

    public function getSentenceCount()
    {
        $text = $this->getFileContent();

        $num_frasi  = count(explode(".\n", $text));
        $num_frasi += count(explode("!\n", $text));
        $num_frasi += count(explode("?\n", $text));

        return $num_frasi;
    }

    private function getFileContent()
    {
        if (file_exists($this->file)) {
            $text = file_get_contents($this->file);
        } else {
            $text = '';
        }

        return $text;
    }
}

$counter = new FileContentCounter('test.txt');
print " - Parole : " . $counter->getWordsCount();
print " - Frasi : " . $counter->getSentenceCount();

file_put_contents('test.txt', 'contenuto');

print " - Parole : " . $counter->getWordsCount();
print " - Frasi : " . $counter->getSentenceCount();