Remove data in txt file after 39 results

Question

Currently I am writing urls to a txt file using the following.

$data['url'] = $element->href;  
$data['image'] = $image->content;   
$data['title'] = $title2->plaintext;    
$data['genre'] = $genre->plaintext;     
file_put_contents('done.txt', $data['url'] . PHP_EOL, FILE_APPEND);

The above is being used inside of a foreach loop, and the website I am collecting data from has 39 results per page, I am wondering how I could delete the previous 39 results on the 40th post without removing the current input flow, that way the txt file has a maximum of 39 urls in it at one time.

EDIT: Sloppy mistake on my part, sorry.

$html = file_get_html('http://oursite.com');         
foreach($html->find('.ourclass') as $element) 
{
    $data['url'] = $element->href;  
    $data['image'] = $image->content;   
    $data['title'] = $title2->plaintext;    
    $data['genre'] = $genre->plaintext;     
    file_put_contents('done.txt', $data['url'] . PHP_EOL, FILE_APPEND);
}

Above is how my foreach is laid out.

Answer 1

Change the flags argument based on the current loop iteration.

Assuming $i is the current iteration index in your foreach loop...

file_put_contents('dont.txt', $data['url'] . PHP_EOL, $i % 39 ? FILE_APPEND : 0);

This will empty the file and start writing new records every 40th iteration.