How does base64_encode in PHP return LF (UNIX) values?

Question

I use Ubuntu server and try to base64_encode a string value but default result return CRLF (Windows), how do return value be LF (UNIX)

<?php
$str = 'this is
       the string
       value in
       my image';
echo base64_encode($str);
?>

LF(UNIX) output:

dGhpcyBpcwp0aGUgc3RyaW5nCnZhbHVlIGluCm15IGltYWdl

CRLF(Windows) output:

dGhpcyBpcw0KdGhlIHN0cmluZw0KdmFsdWUgaW4NCm15IGltYWdl

This is image: enter image description here