PHP复杂的preg_match(PHP Complicated preg_match)

 这是一个很大的范围，但我一直在尝试preg_match和preg_replace，以努力做一些非常复杂的事情。 
 
 我正在尝试使用整个PayPal按钮代码并仅提取13位数的按钮ID号。 我已成功使用preg_replace来获取所有不需要的字符，并将代码暴露为混乱的一行。 不幸的是我也提取了等号 - 我假设我需要从这个新生成的字符串中提取一个值=。 
 
 我面临的第二个问题是，即使我可以在我创建的字符串中留下等号，也有两个以paypal按钮形式存在的值。 现在，我不知何故需要忽略第一个值，只抓住第二个我需要的id。 
 
 我这样做的唯一原因是因为PayPal似乎没有办法复制那个按钮ID。 相反，它会生成整个表单的代码，当您单击它时，它会自动突出显示整个表单代码，不允许您只是突出显示您想要的小部分。 我不得不这样做，以便让不懂代码的人更容易复制表单代码，将其粘贴到表单字段中，让网站自动获取该ID号，然后在我编写的另一个脚本中使用它。 
 
 到目前为止，我有这个： 
 
<?php
$string = '';
$res = preg_replace("/[^a-zA-Z0-9]/", "", $string);
echo $res;
?>
 
 当我将PayPal表单代码添加到顶部的字符串时 - 看起来像这样： 
 
<form target="paypal" action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input type="hidden" name="cmd" value="_s-xclick">
<input type="hidden" name="hosted_button_id" value="D3DPV3Y2WSA4J">
<input type="image" src="https://www.paypalobjects.com/en_US/i/btn/btn_cart_LG.gif" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
<img alt="" border="0" src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" width="1" height="1">
</form>
 
 我得到这个：formtargetpaypalactionhttpswwwpaypalcomcgibinwebscrmethodpostinputtypehiddennamecmdvaluesxclickinputtypehiddennamehostedbuttonidvalueD3DPV3Y2WSA4JinputtypeimagesrchttpswwwpaypalobjectscomenUSibtnbtncartLGgifborder0namesubmitaltPayPalThesafereasierwaytopayonlineimgaltborder0srchttpswwwpaypalobjectscomenUSiscrpixelgifwidth1height1form 
 
 当然，我唯一需要的是第二个值：D3DPV3Y2WSA4J 
 
 我觉得我可以做更多的研究，并弄清楚如何留下等号，所以我的值看起来像：值=但我真的不确定我能跳过第一个值而只抓住第二。 
 
 这对我来说是一次很棒的学习经历 - 因为我不经常使用这样的代码，但是我希望获得更多的知识。 读过这篇文章的人，非常感谢你的时间！ 

It's a far reach but I have been experimenting with both preg_match and preg_replace in an effort to do something extremely complicated.
 
I am trying to take an ENTIRE PayPal button code and extract only the 13-digit button id number. I have successfully used preg_replace to get all of the unwanted characters out and expose the code as one line of a jumbled mess. Unfortunately I extracted the equals signs too-which I assume I will need to extract a value= from this newly generated string.
 
The second issue I face, is even if I can leave the equal signs in the string I have created, there are two values in a paypal button form. Now, I somehow need to ignore the first value and grab only the second which is the id I need.
 
The only reason I am doing this is because PayPal doesn't seem to have a way to copy just that button id. Instead it generates the code for the whole form and when you click on it, it automatically highlights the whole form code not allowing you to simply highlight the small portion you want. I am having to do this to make it simpler for someone who doesn't understand code to copy the form code, paste it in a form field and have the website automatically grab that id number then use it in another script I have written.
 
So far, I have this:
 
<?php
$string = '';
$res = preg_replace("/[^a-zA-Z0-9]/", "", $string);
echo $res;
?>
 
When I add the PayPal form code to the string at the top - which looks like this:
 
<form target="paypal" action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input type="hidden" name="cmd" value="_s-xclick">
<input type="hidden" name="hosted_button_id" value="D3DPV3Y2WSA4J">
<input type="image" src="https://www.paypalobjects.com/en_US/i/btn/btn_cart_LG.gif" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
<img alt="" border="0" src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" width="1" height="1">
</form>
 
I get this: formtargetpaypalactionhttpswwwpaypalcomcgibinwebscrmethodpostinputtypehiddennamecmdvaluesxclickinputtypehiddennamehostedbuttonidvalueD3DPV3Y2WSA4JinputtypeimagesrchttpswwwpaypalobjectscomenUSibtnbtncartLGgifborder0namesubmitaltPayPalThesafereasierwaytopayonlineimgaltborder0srchttpswwwpaypalobjectscomenUSiscrpixelgifwidth1height1form
 
And of course, the only thing I need from that is the second value: D3DPV3Y2WSA4J
 
I feel like I could do a little more research and figure out how to leave the equals signs in so I have the values all looking like: value= but I'm really not sure I will be able to skip the first value and grab only the second.
 
This is all a great learning experience for me - as I do not frequently use code like this but would love to gain more knowledge. Anyone who reads this, thank you so much for your time!

原文：