对于它的价值，这是您正在寻找的正则表达式：
原始匹配模式：
<a ((?:(?!href).)*?)href=[\"\']https:\/\/((?:(?!my-domain.de).)*?)[\"\'](.*?)>(.*?)<\/a>
原始替换模式：
<a $1href="http://$2"$3>$4</a>
PHP代码为：
$content = preg_replace('/<a ((?:(?!href).)*?)href=[\"\']https:\/\/((?:(?!my-domain.de).)*?)[\"\'](.*?)>(.*?)<\/a>/i','<a $1href="http://$2"$3>$4</a>',$content);
话虽如此，但请注意——就Andy Lester 而言，这个正则表达式并不可靠。 虽然在我看来，问题并不完全是“HTML 的本质”，或者至少不那么简单。这个公认的伟大资源——http://htmlparsing.com/regexes——的重点是，你正试图在一条非常崎岖的道路上重新发明轮子。更广泛的关注是“并不是正则表达式本身是邪恶的，而是过度使用正则表达式是邪恶的。”这句话来自杰夫·阿特伍德，来自一个特殊的阐述关于正则表达式的乐趣和恐惧在这里：Regular Expressions: Now You Have Two Problems（他还有一篇文章专门警告不要使用正则表达式解析 HTML——Parsing Html The Cthulhu Way。）
特别是在我上面的“解决方案”的情况下，例如——以下输入（带有行返回）将不匹配，尽管是有效的 HTML：
<a title="mytitle"
href="https://www.other-domain.de/path/index.html"
target="_blank">other domain</a>
但是，以下输入将根据需要进行处理：
<a href="https://my-domain.de">my domain</a>
<a href="https://other-domain.de">other domain</a>
<a href="https://www.my-domain.de/path/index.html">my domain</a>
<a href="https://www.other-domain.de/path/index.html">other domain</a>
<a title="other title" href="https://www.my-domain.de/path/index.html" target="_blank">other domain</a>
<a title="my title" href="https://www.other-domain.de/path/index.html" target="_blank">my domain</a>
变成：
<a href="https://my-domain.de">my domain</a>
<a href="http://other-domain.de">other domain</a>
<a href="https://www.my-domain.de/path/index.html">my domain</a>
<a href="http://www.other-domain.de/path/index.html">other domain</a>
<a title="other title" href="https://www.my-domain.de/path/index.html" target="_blank">other domain</a>
<a title="my title" href="http://www.other-domain.de/path/index.html" target="_blank">my domain</a>
这里有一个很好的资源来解释正则表达式的完整分解：http://www.myregextester.com/index.php
要在该工具上复制测试：
- 选择“替换”操作
- 将您的正则表达式放入“匹配模式”
- 将替换放入“替换模式”
- 选中“i”标志复选框
- 选中“解释”复选框
- 选中“PHP”复选框
- 将您的目标内容放入“源文本”中
- 点击“提交”
为了方便和后代，我在下面包含了该工具提供的完整说明，但其中两个概念性亮点是：
匹配模式说明：
The regular expression:
`(?i-msx:<a ((?:(?!href).)*?)href=[\"\']https:\/\/((?:(?!my-domain.de).)*?)[\"\'](.*?)>(.*?)<\/a>)`
matches as follows:
NODE EXPLANATION
----------------------------------------------------------------------
(?i-msx: group, but do not capture (case-insensitive)
(with ^ and $ matching normally) (with . not
matching \n) (matching whitespace and #
normally):
----------------------------------------------------------------------
<a '<a '
----------------------------------------------------------------------
( group and capture to \1:
----------------------------------------------------------------------
(?: group, but do not capture (0 or more
times (matching the least amount
possible)):
----------------------------------------------------------------------
(?! look ahead to see if there is not:
----------------------------------------------------------------------
href 'href'
----------------------------------------------------------------------
) end of look-ahead
----------------------------------------------------------------------
. any character except \n
----------------------------------------------------------------------
)*? end of grouping
----------------------------------------------------------------------
) end of \1
----------------------------------------------------------------------
href= 'href='
----------------------------------------------------------------------
[\"\'] any character of: '\"', '\''
----------------------------------------------------------------------
https: 'https:'
----------------------------------------------------------------------
\/ '/'
----------------------------------------------------------------------
\/ '/'
----------------------------------------------------------------------
( group and capture to \2:
----------------------------------------------------------------------
(?: group, but do not capture (0 or more
times (matching the least amount
possible)):
----------------------------------------------------------------------
(?! look ahead to see if there is not:
----------------------------------------------------------------------
my-domain 'my-domain'
----------------------------------------------------------------------
. any character except \n
----------------------------------------------------------------------
de 'de'
----------------------------------------------------------------------
) end of look-ahead
----------------------------------------------------------------------
. any character except \n
----------------------------------------------------------------------
)*? end of grouping
----------------------------------------------------------------------
) end of \2
----------------------------------------------------------------------
[\"\'] any character of: '\"', '\''
----------------------------------------------------------------------
( group and capture to \3:
----------------------------------------------------------------------
.*? any character except \n (0 or more times
(matching the least amount possible))
----------------------------------------------------------------------
) end of \3
----------------------------------------------------------------------
> '>'
----------------------------------------------------------------------
( group and capture to \4:
----------------------------------------------------------------------
.*? any character except \n (0 or more times
(matching the least amount possible))
----------------------------------------------------------------------
) end of \4
----------------------------------------------------------------------
< '<'
----------------------------------------------------------------------
\/ '/'
----------------------------------------------------------------------
a> 'a>'
----------------------------------------------------------------------
) end of grouping
----------------------------------------------------------------------