If you want to use variables inside a string, you will have to use a process called variable interpolation. To use it you will have to wrap your variables in #{}
.
Consider:
$name: 'Gajendar';
$author: 'Author : $name'; // 'Author : $name'
$author: 'Author : #{$name}';
// 'Author : Gajendar'
The interpolation method could be useful in situations where the value of a variable is determined by some conditional statements.