(PHP) fwrite doesn't write but overwrite - php

Question

I want to open the .xml file and write the content of the $xml_doc variable into the file. The problem is, when the file is empty, it refuses to write. It only writes when there is already some text (abc123 for example). I tried to change mode of fopen function to a, a+, w, w+, and w, w+ are simply erase the file content but write nothing.
if($telecharger) {
// Creation du fichier
$nom = "PRELEVEMENT";
$filename= "/home/alc/alcg_si/alcgroup/intranet/documents/prelevement_xml/".$nom."__".$date_prev.".xml";
try {
$file = fopen($filename, 'r+') or die("Error: can't open file.");
chmod($filename, 0777);
fwrite($file, '$xml_doc') or die("Error: can\'t write in file.");
fclose($file);
} catch (Exception $e) {
echo "MERDEEEE<br>";
echo 'Caught exception: ', $e->getMessage(), "\n";
}

Answer 1

File permissions are checked when opening the file. If the file permissions don't allow writing, you need to call chmod() before calling fopen().
You can also replace all the code that calls fopen, fwrite, and fclose with a single call to file_put_contents().
And don't put the variable $xml_doc in single quotes, that prevents expanding the variable. It will write the literal string $xml_doc to the file.
if($telecharger) {
// Creation du fichier
$nom = "PRELEVEMENT";
$filename= "/home/alc/alcg_si/alcgroup/intranet/documents/prelevement_xml/".$nom."__".$date_prev.".xml";
try {
if (file_exists($filename)) {
chmod($filename, 0644) or die("Error: can't change file permissions");
}
file_put_contents($filename, $xml_doc) or die("Error: can\'t write in file.");
} catch (Exception $e) {
echo "MERDEEEE<br>";
echo 'Caught exception: ', $e->getMessage(), "\n";
}