Remove a certain variable from a query string - php

Question

How do I remove a certain variable from a query string? Say I have a query string
$query_string = "first=val1&second=val2&third=val3";
function removevar($var, $query_string) {
return preg_replace("/(".$var."=[^&]*(&))/i","",$query_string);
}
echo removevar("first",$query_string); // ok
echo removevar("second",$query_string); // ok
echo removevar("third",$query_string); // doesn't change the string because third doesn't have a trailing &
How can this be fixed so that it removes variables from a query string in a robust way? Probably someone already has a function that does this along with special cases in more complex strings.
So I'd have to match either & or end of the string ($) but I don't know how to turn that into regex.

Answer 1

$query_string = "first=val1&second=val2&third=val3";
function removevar($var, $query_string) {
return preg_replace("/(".$var."=[^&]*(&|$))/i","",$query_string);
}
echo removevar("first",$query_string); // ok
echo removevar("second",$query_string); // ok
echo removevar("third",$query_string); // ok
This should do the trick.

Answer 2

You don’t necessarily need regular expressions for this as PHP does have functions that can parse and build query strings (parse_str and http_build_query respectively):
function removevar($var, $query_string) {
parse_str($query_string, $args);
unset($args[$var]);
return http_build_query($args);
}
Note that you need to decode the HTML character references before using these functions.

Answer 3

You will probably have more luck using:
html_entity_decode to get the 'normal' query-string.
parse_str to get the query string into an array.
unset the desired key in that array.
Use http_build_query to rebuild the string.
Call htmlspecialchars on it to get the & back to &.
Less concise than the regex route, but a lot less error-prone.

Answer 4

<?php
$query_string = "first=val1&second=val2&third=val3";
parse_str($query_string, $output);
function removevar($var, $output_array) {
if (in_array($var, $output_array)) {
unset($output_array[$var]);
}
return http_build_query($output_array, '', '&');
}
echo removevar("first", $output);
echo removevar("third", $output);
?>
Normally for codes like this, which involves a query string, it is always best to go for the in-built PHP functions rather than for the regex syntax / formula. That is what I've done, and the main parts of the code include the following PHP in-built functions:-
parse_str Function
in_array Function
http_build_query Function
Hope it helps.

Answer 5

function removevar($var, $query_string) {
$query_string = preg_replace("#$var=([^&]+)#is", "", $query_string);
return trim($query_string, "&");
}

Answer 6

There are functions, that can handle query strings directly.
function removevar ($var, $query_string) {
$array = array();
parse_str(html_entity_decode($query_string), $array);
unset($array[$var]);
return html_entities(http_build_query($array);
}