I can use str_replace to replace all the occurrences of a string with a different value, but what's the most efficient way to do this for a file?

thanks

<?php

function str_replace_file( $search, $replace, $filename )
{
$fp = fopen( $filename, "w+" );
fwrite( $fp, str_replace( $search, $replace, fread( $fp, filesize( $filename ) ) ) );
fclose( $fp );
}

?>