There is a huge diference in speed with these two approaches:

$file=file("file.txt");

1.
 for($i=0;$i<sizeof($file);$i++)
   ...

2.
$file_size=sizeof($file);
 for($i=0;$i<$file_size;$i++)
    ...

The second approach is much more faster, because the first seems to calculate the 'sizeof' in every iteration.