- substr: documentation ( source)
- strpos: documentation ( source)
<?php
//$utf8string = 'ASCIIユーティーエッフ8hello123等々';
$utf8string = 'ASCIIhello123';
$var = 'hello123';
$pos = strpos($utf8string, $var);
if ($pos!==false) {
echo substr($utf8string, 0, $pos);
}