Php url query parameter

Beginners Guide $GET Query Strings URL Parameters In PHP Coding Lesson 7

This is our beginners guide to PHP Query string url parameters. After completing this lesson you will have a general knowledge of PHP’s $GET function with parameters. Let’s break down the code in this lesson and see how PHP Query Strings work. Here are the files for this lesson.

What Are Query String Parameters In PHP?

A Query String Parameter is usually associated with a search feature. Think of a query string as a question. Think of the parameter as the operator. Let’s illustrate this with a simple example. Here is our question.

If we pop this question into Google, Bing or Yahoo you will notice something in the URL. Notice at the top in the web address where it reads “search/?q=”. This is the start of the query string. The question mark with the letter “q” is the parameter. Our search in this instance only had one query term. “php”.

How Do Multi Parameters Work In PHP Query Strings?

Multi parameters take in more that one term. In our example below in the query string there are 3 parameters.

The parameters are separated by an ampersand “&” and followed by an equal sign “=”. Except for the first parameter. The first parameter starts with a question mark “?” then the parameter “q” followed by an equals sign “=”.

If you would like a detailed explanation of the Google Parameters in their search engine see this article. In this lesson we are just going to name what they are so we can implement it in our PHP programming.

How To Get Query String Parameters In PHP

You may be wondering how to get a query string and show it in a page within the HTML. Well, if your parameter is the letter q your URL would look something like this.

To get whatever is in the parameter of “q” you would use this php code somewhere on the page.

The print out on the page would look like this, “foo”.

If you wanted more that one term in your parameter you would separate it in the URL with the plus “+” sign. Here is an example.

https://example.com/foo.php?q=foo+doo

This will print out on the page, “foo doo”.

Using Multi Parameters In URL for PHP Query Strings

So there may come a time when you need to set multi parameters in your URLs. You would set up the URL for multi parameters like this.

https://example.com/foo.php?q=foo&w=doo

To get those parameters with PHP you would use a code like this.

PHP Error Notice: Undefined index:

The problem with the above codes is that if you do not have the parameters loaded in the URL, PHP will give an error notice of undefined index. In the old days before PHP7 we use to handle that error like this.

Now In PHP7 We can write the code like this, this is called the “null coalescing operator (??)” a new feature in Php 7.

If there is nothing in the URL parameter it would read, “not passed”. However, if you wanted it to show nothing you could write it like this.

Conclusion Query String Parameters in PHP

I hope you enjoyed this lesson on Query String Parameters in PHP. In our next lesson we will be working with forms and processing them in PHP. Please join us. Like share and subscribe if you want the next lesson.

Beginners Guide $GET Query Strings URL Parameters In PHP Coding Lesson 7 was last modified: October 29th, 2021 by Maximus Mccullough

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Get Query String from URL in php

To get the query string from a URL in php, you can use $_GET super global to get specific key value pairs or $_SERVER super global to get the entire string.

// http://theprogrammingexpert.com/?key1=value1&key2=value2&key3=value3 echo $_GET['key1']; echo $_GET['key2']; echo $_SERVER['QUERY_STRING']; //Output: value1 value2 key1=value1&key2=value2&key3=value3

A query string is a part of a URL that assigns values to specified parameters. When building web pages, query strings help us pass and access information to be used on our web pages.

When working in php, the ability to easily access and work with query strings is important.

To get a query string from a URL, there are a few different ways you can get the key value pairs.

To get a specific parameter from a query string, you can use $_GET super global to access individual parameters from the query string by name.

// http://theprogrammingexpert.com/?key1=value1&key2=value2&key3=value3 echo $_GET['key1']; //Output: value1

If you want to get the entire query string, you can use the $_SERVER super global.

// http://theprogrammingexpert.com/?key1=value1&key2=value2&key3=value3 echo $_SERVER['QUERY_STRING']; //Output: key1=value1&key2=value2&key3=value3

After getting the entire query string, you can parse it for the key value pairs with the php parse_str() function.

Using $_GET to Get Query String Parameters in php

The $_GET super global variable allows us to get individual key value pairs from query strings.

There are a few additional cases which occur when using query strings that I want to share with you.

First, in a query string, you can have duplicate key names followed by square brackets. This will create a child array in $_GET for that key with numerically indexed values.

// http://theprogrammingexpert.com/?key[]=value1&key[]=value2&key[]=value3 echo $_GET['key'][0]; echo $_GET['key'][1]; echo $_GET['key'][2]; //Output: value1 value2 value3

If the brackets are not empty, and have keys in them, then for a particular key, the child array belonging to the key will be an associative array.

// http://theprogrammingexpert.com/?key[ex1]=value1&key[ex2]=value2&key[ex3]=value3 echo $_GET['key']['ex1']; echo $_GET['key']['ex2']; echo $_GET['key']['ex3']; //Output: value1 value2 value3

Using $_SERVER to Get Query String in php

You can also use the $_SERVER super global variable to get the entire query string. After getting the query string, you can parse it with the php parse_str() function.

// http://theprogrammingexpert.com/?key1=value1&key2=value2&key3=value3 query_string = $_SERVER['QUERY_STRING']; parse_str(query_string); echo $key1; echo $key2; echo $key3; //Output: value1 value2 value3

Hopefully this article has been useful for you to learn how to get query strings and work with them in php.

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How to retrieve URL parameters in PHP.

In this beginner PHP tutorial, we will show you how to retrieve query string parameters from a URL. We will also tell you about some of the most common pitfalls.

Take the following URL as an example, which contains two GET parameters:

In the URL above, we have two GET parameters. id, which contains the value 23, and page, which contains the value 34.

Let’s say that we want to retrieve those values so that we can use them in our PHP script.

If we want to retrieve the values of those two parameters, we can access the $_GET superglobal array like so:

//Get our two GET parameters. $id = $_GET['id']; $page = $_GET['page'];

Although the PHP code will work, it wrongly assumes that the GET parameters in question will always exist.

As a result, there is a possibility that our script will throw an ugly undefined index notice if a user removes one of the parameters from the URL.

This will result in PHP spitting out the following message:

Notice: Undefined index: id in /path/to/file.php on line 4

To guard against this kind of issue, you will need to check to see if the GET variable exists before you attempt to use it:

$id = false; if(isset($_GET[‘id’])) < $id = $_GET['id']; >$page = false; if(isset($_GET[‘page’]))

In the example above, we use PHP’s isset function to check whether or not the parameter in question actually exists.

If it does exist, we assign it to one of our variables. If it doesn’t, then our variables will retain their default FALSE values.

Never trust GET parameters. Always validate them.

GET parameters should always be treated with extreme caution.

1. You cannot assume that they will always exist.
2. If they do exist, you can’t discount the possibility that the user has tampered with them.

In other words, if you expect id to be an integer value and a user decides to manually change that to “blahblahblah”, your PHP script should be able to handle that scenario.

URL parameters are external variables, and external variables can never ever be trusted.

Never directly print GET parameters onto the page.

Printing out GET parameters without sanitizing them is a recipe for disaster, as it will leave your web application wide open to XSS attacks.

Take the following example:

$page = false; if(isset($_GET['page'])) < $page = $_GET['page']; >if($page !== false)< echo '
Page: ' . $page . '
'; >

Here, we’ve done everything right except the final step:

1. We check to see if the GET parameter exists before we access its value.
2. We do not print the page number out if it doesn’t exist.

However, we did not sanitize the variable before we printed it out. This means that an attacker could easily replace our GET variable with HTML or JavaScript and have it executed when the page is loaded.

They could then redirect other users to this “tainted” link.

To protect ourselves against XSS, we can use the PHP function htmlentities:

//Guarding against XSS if($page !== false)< echo '
Page: ' . htmlentities($page) . '
'; >

The htmlentities function will guard against XSS by converting all special characters into their relevant HTML entities. For example, will become <script>

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