如何重写同一个文件

Question

Currently I'm doing it like this:

$f = fopen('test', 'w');
fwrite($f, 'Hi');
fclose($f);

But I have a loop that does some expensive stuff (with files), and I'd like to avoid opening and closing the file handle every time I want to overwrite "test"

It should be something like this:

$f = fopen('test', 'w');

$i = 0;
while($ < 50000){

  $i++;
  foverwrite($f, 'i = ' . $i);

  sleep(5); // just a example

}

fclose($f);

Is this possible?

This script runs in the background in CLI mode and I'm reading the test file from the web with ajax like every 2 seconds. Basically I'm trying to display a progress bar lol

Answer 1

You can update the content of a file by rewinding the file pointer, see fseek() . Be careful, once you set file lenght to N by writing N bytes to it, next time, if you rewind and write X < N bytes, the file will remain N bytes long, containing X bytes of new data and NX bytes of old stuff.

Anyway, don't worry about opening and closing files several times, they will be cached. Or you can open it on a ramdisk partition.

Answer 2

You can keep the file and just rewrite over the contents, while then truncating the file if the size changed. This will be faster than overwriting or deleting and rewriting.

$f = fopen('test', 'w');
$i = 0;
while($i < 50000){
  $i++;

  rewind($f);
  $data = 'i = ' . $i;
  fwrite($f, $data);
  ftruncate($f, strlen($data)); // <---------- Here's the ticket

  sleep(5);
}

fclose($f);

Answer 3

To go along with your example, you could implement your foverwrite() function using frewind() like this:

function foverwrite($handle,$content)
  {
  frewind($handle);
  return fwrite($handle,$content);
  }

This function will return fwrite() 's return value, so it can readily replace fwrite() where needed. Also, in case of opening the file in append mode (a or a+) it will just append contens, as frewind() will make no difference.

However, concerning the purpose of your script, which clearly is interprocess communication , you should take a look at more efficient techniques, like shared memory .

Answer 4

You can do it in following ways

$data = [];//initiate the $data variable as empty array
$i = 0;
while($i < 50000){

  $data[] = 'i = ' . $i;
  $i++;
}
file_put_contents('file.txt', implode("\n", $data));// implode the array

Answer 5

If you're just aiming to keep a file updated so that it can be accessed by AJAX requests, then do you really need to update it 50000 times? A simple way of cutting your overhead would be to update the file less often. Like this, for example:

for ($i=0; $i<50000; $i++) {

  // update progress file every 1000 iterations:
  if (!($i % 1000)) file_put_contents('./file.txt', "i = $i");

  // --- do stuff ---

}
file_put_contents($f, "i = 50000");