$fp = fopen("/tmp/my-data.txt", "w");
if (flock($fp, LOCK_EX)) { 
   // do an exclusive/write lock. use LOCK_SH (for  shared/read lock)
   fwrite($fp, "Write something here\n");
   flock($fp, LOCK_UN); // release the lock
} else {
   echo "Couldn't lock the file !";
}
fclose($fp);

rename($oldname, $newname); //like Unix mv command, renames/moves a file
copy($source, $dest); //copies a file, like Unix cp
unlink($filename); // delete a file
mkdir($path); // make a directory
rmdir($path); // delete a directory
link($target, $name); // create a link
chmod($filename, $mode); // change file permissions
chown($filename, $user); // change owner of a file or dir or link
chgrp($filename, $group); //change group of a file or dir or link
stat($filename); 
   //returns an array saying size, last access, last modified, etc.  for a file
touch($filename [, int $time = time() [, int $atime ]]); 
   //sets modification/ access times of a file

if(file_exists('/path/to/folder')) { //file_exists check if a file or dir exists
    $h = opendir('/path/to/folder'); //can use is_dir to check is something is a directory
    while (($item = readdir($h)) !== false) {
        $type = is_dir($item) ? "directory" : 
            (is_link($item) ? "link" : 
            "file");
        //there is also a is_file
        echo "$item is a $type\n";
    }
}

$text_files = glob("/some_path/*.txt");
foreach($text_files as $file_name) {
   //do something
}

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