remove a part of a URL argument string in php

I have a string in PHP that is a URI with all arguments:

$string = http://domain.com/php/doc.php?arg1=0&arg2=1&arg3=0

I want to completely remove an argument and return the remain string. For example I want to remove arg3 and end up with:

$string = http://domain.com/php/doc.php?arg1=0&arg2=1

I will always want to remove the same argument (arg3), and it may or not be the last argument.

Thoughts?

EDIT: there might be a bunch of wierd characters in arg3 so my prefered way to do this (in essenc开发者_开发问答e) would be:

$newstring = remove $_GET["arg3"] from $string;

There's no real reason to use regexes here, you can use string and array functions instead.

You can explode the part after the ? (which you can get using substr to get a substring and strrpos to get the position of the last ?) into an array, and use unset to remove arg3, and then join to put the string back together.:

$string = "http://domain.com/php/doc.php?arg1=0&arg2=1&arg3=0";
$pos = strrpos($string, "?"); // get the position of the last ? in the string
$query_string_parts = array();

foreach (explode("&", substr($string, $pos + 1)) as $q)
{
  list($key, $val) = explode("=", $q);
  if ($key != "arg3")
  {
    // keep track of the parts that don't have arg3 as the key
    $query_string_parts[] = "$key=$val";
  }
}

// rebuild the string
$result = substr($string, 0, $pos + 1) . join($query_string_parts);

See it in action at http://www.ideone.com/PrO0a

preg_replace("arg3=[^&]*(&|$)", "", $string)

I'm assuming the url itself won't contain arg3= here, which in a sane world should be a safe assumption.

$new = preg_replace('/&arg3=[^&]*/', '', $string);

This should also work, taking into account, for example, page anchors (#) and at least some of those "weird characters" you mention but don't seem worried about:

function remove_query_part($url, $term)
{
    $query_str = parse_url($url, PHP_URL_QUERY);
    if ($frag = parse_url($url, PHP_URL_FRAGMENT)) {
        $frag = '#' . $frag;
    }
    parse_str($query_str, $query_arr);
    unset($query_arr[$term]);
    $new = '?' . http_build_query($query_arr) . $frag;
    return str_replace(strstr($url, '?'), $new, $url);
}

Demo:

$string[] = 'http://domain.com/php/doc.php?arg1=0&arg2=1&arg3=0';
$string[] = 'http://domain.com/php/doc.php?arg1=0&arg2=1';
$string[] = 'http://domain.com/php/doc.php?arg1=0&arg2=1&arg3=0#frag';
$string[] = 'http://domain.com/php/doc.php?arg1=0&arg2=1&arg3=0&arg4=4';
$string[] = 'http://domain.com/php/doc.php';
$string[] = 'http://domain.com/php/doc.php#frag';
$string[] = 'http://example.com?arg1=question?mark&arg2=equal=sign&arg3=hello';

foreach ($string as $str) {
    echo remove_query_part($str, 'arg3') . "\n";
}

Output:

http://domain.com/php/doc.php?arg1=0&arg2=1
http://domain.com/php/doc.php?arg1=0&arg2=1
http://domain.com/php/doc.php?arg1=0&arg2=1#frag
http://domain.com/php/doc.php?arg1=0&arg2=1&arg4=4
http://domain.com/php/doc.php
http://domain.com/php/doc.php#frag
http://example.com?arg1=question%3Fmark&arg2=equal%3Dsign

Tested only as shown.