- stream_get_meta_data: documentation ( source)
- fopen: documentation ( source)
<?php
$modes = ['w', 'a', 'x', 'c', 'wb', 'ab', 'xb', 'cb', 'wt', 'at', 'xt', 'ct'];
foreach($modes as $mode) {
$stream = fopen('php://memory', $mode);
$stats = stream_get_meta_data($stream);
echo $stats['mode'].PHP_EOL;
}