PHP删除内容中的部分URL

I have a string which contains a varying number of Url's. I would like to remove the "?category_id=x" part of every Url. x will be a changing number.

var old_string = "some text <a href='/platforms/item/something?category_id=x'>some text</a> some more text <a href='/platforms/item/something?category_id=x'>some text</a>..." 

var new_string = "some text <a href='/platforms/item/something'>some text</a> some more text <a href='/platforms/item/something'>some text</a>...." 

How can I do this. Regex?

Answers using parse_url are best if you've already extracted the URLs from your string. I'm assuming you have not.

<?php
$old_string = "some text <a href='/platforms/item/something?category_id=x'>some text</a> some more text <a href='/platforms/item/something?category_id=x'>some text</a>...";

// if you know there won't be any other url parameters:
$new_string = preg_replace('!\?category_id=(x|\d+)!','', $old_string );

// otherwise, remove query string from all URLs:
$new_string = preg_replace('!(href=(?:\'|")[^\?\'"]+)\?[^\'"#]*!','\1', $old_string );

Your code looks like JavaScript though. The second regexp in JS would be:

old_string.replace( /(href=(?:"|')[^\?'"]+)\?[^'"#]*/g, '$1' );

There is the parse_url function that allows to separate the components of an url string.

http://php.net/manual/en/function.parse-url.php

<?php
$url = '//www.example.com/path?googleguy=googley';   
var_dump(parse_url($url));
?>

Output:-

array(3) {
  ["host"]=>
  string(15) "www.example.com"
  ["path"]=>
  string(5) "/path"
  ["query"]=>
  string(17) "googleguy=googley"
}

Source:- http://php.net/manual/en/function.parse-url.php

<?php
 $old_string  = "some text <a href='/platforms/item/something?category_id=x'>some text</a>  some more text <a href='/platforms/item/something?category_id=x'>some text</a>...";
 preg_match( '/<a href=\'(.*?)\'>/', $old_string, $match );
 $url         = parse_url($match[1]) ;
 $new_string  = "some text <a href='".$url["host"].$url["path"];
 $new_string .= "'>some text</a> some more text <a href='/platforms/item/something?    category_id=x'>some text</a>...";
 echo htmlentities($new_string);
//output
// some text <a href='/platforms/item/something'>some text</a> some more text <a  href='/platforms/item/something?category_id=x'>some text</a>...
?>