<?PHP
$string = 'cup';
$name = 'coffee';
$str = 'This is a $string wITh my $name in it.';
echo $str. "\n";
eval("\$str = \"$str\";");
echo $str. "\n";
?>

以上示例将输出：

This is a $string with my $name in it.
This is a cup with my coffee in it.

http://php.net/manual/en/function.eval.php

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