Question

I need to change a single character in a file.
I’d rather not use an auxiliary file like so (pseudo code):
read(theFile)

change(theFile)

write(theFile2)

erase(theFile)

rename(theFile2,theFile)

Since in this way, Some process can require that file when it is actually erased.
Rather, I’d like to operate on that own file, because this way, I count on the server’s os to take care of timing and process access to the file.

Answer 1

You’ll want to use flock to lock the file. Example based on code from the PHP docs:

<?php

$fp = fopen("file.txt", "r+");

if (flock($fp, LOCK_EX)) {  // acquire an exclusive lock
    //make your changes
    fflush($fp);            // flush output before releasing the lock
    flock($fp, LOCK_UN);    // release the lock
} else {
    echo "Couldn't get the lock!";
}

fclose($fp);

?>