PHP Fatal error: Undefined class constant 'WRITE_SCOPE' - php

Question

I use PHP app in Google appengine,
I'm trying to read a input file and write it to an output file in Storage bucket like below.
$input_file = fopen('gs://mybucket/input.csv','r');
$output_file = fopen('gs://mybucket/output.csv', 'w');
And trying to write some date like
while(!feof($input_file)) {
$csv = fgetcsv($input_file,1024);
if(!$csv[0]){
fclose($output_file); //Close the connection when the loop ends
fclose($input_file);
exit(0);
}
fwrite($output_file, $csv[0]."\r\n");
}
It works perfectly, When i try to upload some data in to input file and it successfully write in to output.csv as well. but if i try more than 5 or 6th time it starts to throw an error in appengine logs like below. Any help to troubleshoot this issue will be highly appreciated!
2015-04-08 21:31:29.006 PHP Fatal error: Undefined class constant 'WRITE_SCOPE' in /base/data/home/runtimes/php/sdk/google/appengine/ext/cloud_storage_streams/CloudStorageWriteClient.php on line 214
Update:
I think this is because of opening 2 file streams at same time,
Did some work around and solved this!
$input_file = fopen('gs://mybucket/input.csv','r');
$array_acc = array();
while(!feof($input_file)) {
$csv = fgetcsv($input_file, 1024);
if($csv[0]) array_push($array_acc, $csv[0]);
}
fclose($input_file); //close the file
$acc_count = count($array_acc);
$output_file = fopen('gs://tool-synclio/output.csv','w'); // Open the output file now
while($acc_count > 0){
fwrite($output_file,$array_acc[$acc_count]."\r\n");
$acc_count --;
}
fclose($output_file);
But, I'm still waiting for some one to give better solution.

Answer 1

You have 2 dollar signs in a variable:
fwrite($output_file, $$csv[0]."\r\n");