2019-01-06-read-array from file update and save.

$decoded = array();
$file_name = "data/".date('y-m-d').".txt";

//Retrieve the data from our text file.
$fileContents = file_get_contents($file_name);

//Convert the JSON string back into an array.
$decoded = json_decode($fileContents, true);

//Example array.

$decoded[] = date("H:i:s");

//Encode the array into a JSON string.
$encodedString = json_encode($decoded);

//Save the JSON string to a text file.
file_put_contents($file_name, $encodedString);

//The end result.
var_dump($decoded);