PHP Reading A File |and| Writing To A File

document.txt
this is the first line.
this is the second line.

this is the fourth line.

getfile.php

<?php

//header('Content-Type: text/plain');

$file = "./document.txt";
$document = file_get_contents($file);

echo $document;

$lines = explode("\n",$document);
foreach($lines as $newline){
echo '<b>' . $newline . '</b><br>';
}

?>

fileput.php

<?php
$file = "./lines.txt";
$write = "this is line one\n";

file_put_contents($file,$write);
//file_put_contents($file,$write,FILE_APPEND);

?>

php -> fwrite()

<?php

//file write
//$h = fopen('data.txt','w+');
//fwrite($h,'hello zxl');
?>

-->data.txt

==>hello zxl