是否可以在单引号字符串中插入变量？

<?php $header_string = '<a href="get_bloginfo('url')">Holiday</a>'; ?>

How do I insert get_bloginfo('url') correctly inside the single quoted string above?

<?php $header_string = '<a href="' . get_bloginfo('url') . '">Holiday</a>'; ?>

Note the use of the dots (.), which are used for concatenating strings.

Use concatenation

<?php $header_string = '<a href="'.get_bloginfo('url').'">Holiday</a>'; ?>