(PHP 5 >= 5.1.0)
SplFileObject::fseek — Seek to a position
$offset
   [, int $whence = SEEK_SET
  ] )
   Seek to a position in the file measured in bytes
   from the beginning of the file, obtained by adding
   offset to the position specified by
   whence.
  
offset
       The offset. A negative value can be used to move backwards through the file which
       is useful when SEEK_END is used as the whence value.
      
whence
       whence values are:
       
SEEK_SET - Set position equal to offset bytes.SEEK_CUR - Set position to current location plus offset.SEEK_END - Set position to end-of-file plus offset.
       If whence is not specified, it is assumed to be SEEK_SET.
      
Returns 0 if the seek was successful, -1 otherwise. Note that seeking past EOF is not considered an error.
Example #1 SplFileObject::fseek() example
<?php
$file = new SplFileInfo("somefile.txt");
// Read first line
$data = $file->fgets();
// Move back to the beginning of the file
// Same as $file->rewind();
$file->fseek(0);
?>