Is this the most efficient way to get and remove first line in file?

Question

I have a script which, each time is called, gets the first line of a file. Each line is known to be exactly of the same length (32 alphanumeric chars) and terminates with \"

Answer 1

No need to create a second temporary file, nor put the whole file in memory:

if ($handle = fopen("file", "c+")) {             // open the file in reading and editing mode
    if (flock($handle, LOCK_EX)) {               // lock the file, so no one can read or edit this file 
        while (($line = fgets($handle, 4096)) !== FALSE) { 
            if (!isset($write_position)) {        // move the line to previous position, except the first line
                $write_position = 0;
            } else {
                $read_position = ftell($handle); // get actual line
                fseek($handle, $write_position); // move to previous position
                fputs($handle, $line);           // put actual line in previous position
                fseek($handle, $read_position);  // return to actual position
                $write_position += strlen($line);    // set write position to the next loop
            }
        }
        fflush($handle);                         // write any pending change to file
        ftruncate($handle, $write_position);     // drop the repeated last line
        flock($handle, LOCK_UN);                 // unlock the file
    }
    fclose($handle);
}