(PHP 5 >= 5.1.0)
SplFileObject::fwrite — Write to file
$str
   [, int $length
  ] )
   Writes the contents of string to the file
  
strThe string to be written to the file.
length
       If the length argument is given, writing will
       stop after length bytes have been written or
       the end of string is reached, whichever comes
       first.
      
   Returns the number of bytes written, or NULL on error.
  
Example #1 SplFileObject::fwrite() example
<?php
$file = new SplFileObject("fwrite.txt", "w");
$written = $file->fwrite("12345");
echo "Wrote $written bytes to file";
?>
The above example will output something similar to:
Wrote 5 bytes to file