<?php
$show_value = 123;
echo 'sing_quote'.$show_value;
echo "double_quote{$show_value}";
?>
Its opcode is:
1: <?php
2: $show_value = 123;
0 ASSIGN !0, 123
3: echo 'sing_quote'.$show_value;
1 CONCAT 'sing_quote', !0 =>RES[~1]
2 ECHO ~1
4: echo "double_quote{$show_value}";
3 ADD_STRING 'double_quote' =>RES[~2]
4 ADD_VAR ~2, !0 =>RES[~2]
5 ECHO ~2
6 RETURN 1