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

The above example will show:

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

手册里面的例子不是很清楚哦。请教哪位大虾好好讲一下，举一些例子。