php; remove single variable value pair from querystring - php

Question

I have a page that lists out items according to numerous parameters ie variables with values.
listitems.php?color=green&size=small&cat=pants&pagenum=1 etc.
To enable editing of the list, I have a parameter edit=1 which is appended to the above querystring to give:
listitems.php?color=green&size=small&cat=pants&pagenum=1&edit=1
So far so good.
WHen the user is done editing, I have a link that exits edit mode. I want this link to specify the whole querystring--whatever it may be as this is subject to user choices--except remove the edit=1.
When I had only a few variables, I just listed them out manually in the link but now that there are more, I would like to be able programmatically to just remove the edit=1.
Should I do some sort of a search for edit=1 and then just replace it with nothing?
$qs = str_replace("&edit=1, "", $_SERVER['QUERY_STRING']);
<a href='{$_SERVER['PHP_SELF']}?{$qs}'>return</a>;
Or what would be the cleanest most error-free way to do this.
Note: I have a similar situation when going from page to page where I'd like to take out the pagenum and replace it with a different one. There, since the pagenum varies, I cannot just search for pagenum=1 but would have to search for pagenum =$pagenum if that makes any difference.
Thanks.

Answer 1

I'd use http_build_query, which nicely accepts an array of parameters and formats it correctly. You'd be able to unset the edit parameter from $_GET and push the rest of it into this function.
Note that your code has a missing call to htmlspecialchars(). A URL can contain characters that are active in HTML. So when outputting it into a link: Escape!
Some example:
unset($_GET['edit']); // delete edit parameter;
$_GET['pagenum'] = 5; // change page number
$qs = http_build_query($_GET);
... output link here.

Answer 2

Here's my shot:
/**
* Receives a URL string and a query string to remove. Returns URL without the query string
*/
function remove_url_query($url, $key) {
$url = preg_replace('/(?:&|(\?))' . $key . '=[^&]*(?(1)&|)?/i', "$1", $url);
$url = rtrim($url, '?');
$url = rtrim($url, '&');
return $url;
}
Returns:
remove_url_query('http://example.com?a', 'a') => http://example.com
remove_url_query('http://example.com?a=1', 'a') => http:/example.com
remove_url_query('http://example.com?a=1&b=2', 'a') => http://example.com?b=2
Kudos to David Walsh.

Answer 3

Another solution, to avoid & problems too!!!
remove_query('http://example.com/?a=valueWith**&**inside&b=value');
Code:
function remove_query($url, $which_argument=false){
return preg_replace('/'. ($which_argument ? '(\&|)'.$which_argument.'(\=(.*?)((?=&(?!amp\;))|$)|(.*?)\b)' : '(\?.*)').'/i' , '', $url);
}

Answer 4

It wouldn't work if edit=1 is the first variable:
listitems.php?edit=1&color=green&...
You can use the $_GET variable to create the query string yourself. Something like:
$qs = '';
foreach ($_GET as $key => $value){
if ($key == 'pagenum'){
// Replace page number
$qs .= $key . '=' . $new_page_num . '&';
}elseif ($key != 'edit'){
// Keep all key/values, except 'edit'
$qs .= $key . '=' . urlencode($value) . '&';
}
}