php - PHP 中的这种语法是什么？

Question

$test= <<<EOF

....

EOF;

我从来没有见过它。它有什么用？

Answer 1

这叫做 HEREDOC syntax ，这是一种在多行上使用变量插值定义字符串的方法。

引用手册页:

Heredoc text behaves just like a double-quoted string, without the double quotes. This means that quotes in a heredoc do not need to be escaped, but the escape codes listed above can still be used. Variables are expanded, but the same care must be taken when expressing complex variables inside a heredoc as with strings.

(还有更多要阅读，我没有从手册页复制粘贴)

并且，作为一个非常快速和简单的例子:

$a = 'World';
$string = <<<MARKER
<p>
  Hello, $a!
</p>
MARKER;
echo $string;

它会给你这个输出:

Hello, World!

还有这个 HTML 源代码:

<p>
  Hello, World!
</p>