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A Uniform Resource Locator (URL), otherwise known as a Universal Resource Locator, is the address of a resource on the Internet and the protocol used to access it.
It indicates the location of a web resource like a street address indicates where a person lives physically — because of this, an URL is often referred to as: “web address”.
A URL contains the following information:
The protocol used to access the resource.
The location of the server (whether by IP address or domain name).
The port number on the server (optional).
The location of the resource in the directory structure of the server.
A fragment identifier (optional).
A URL is a type of uniform resource identifier (URI). In common practice, the term URI isn't used, or is used synonymously with URL, even though this is technically incorrect.
Users browsing the Internet use URLs and use them by typing or copy-pasting them in their web browser’s address bar.
Also, every time you click on a hyperlink inside an application (email, web page, word document), you are effectively being redirected to that URL.
All URLs are presented in the following order:
Colon and two slashes.
Location of the server.
The port (optional) and the location of the resource on the server.
Fragment identifier (optional).
So, the format will look like this:
This looks more complex than it actually is. The most common schemes (protocols) are HTTP and HTTPS, which any www-user will recognize. The location of the server is generally a domain name, such as Google.com.
Given this, the following URLs are much simpler to understand:
Both these URLs indicate that there is a file named default.htm on a server with the address of "google.com". One uses regular HTTP, while the other uses a secure version of this scheme.
The "www" isn’t always part of the technical protocol. Websites just started using this to indicate the user is using the World Wide Web. This is why if you go to http://google.com, it redirects to http://www.google.com. However, how the domain name is set up is based on how the web server and network administrators set it up in the backend.
Most users access the internet via a web browser, which inserts port 80 on HTTP connections behind the scenes. This is why if you go to http://www.google.com:80, you will see the same website as if there were no port number. A different network port could still be specified to make the connection to a particular destination. You can append user input, query parameters, or values to a URL depending on the configuration of the web server where that particular resource is hosted on.
Finally, the following URL demonstrates a fragment identifier, more commonly known as a query string:
This is saying that to use the HTTP protocol to send a request to the web resource (at google.com over port 80) passing into the resource a list of required input parameters via a set of key/value pairs. The key is the variable name (“hello”) and the value is the input ("some-page").
This is why you'll sometimes see an extremely long URL as many variables are being sent to the web server in more interactive Web applications or dynamic pages like a search engine.
A broad range of other fragments is also used to specify the details of a destination, such as the # (hashtag) that directs the user to a specific view of a page.
For example, the #Examples fragment in this URL redirect the user to the “Examples” section of the Fragment Identifier page in the Wikipedia:
URLs can be redirected or forwarded to a different URL in several ways, the most common of which are 301 (permanent) and 302 (temporary). URL redirection is used to ensure that a visitor doesn’t end up on a 404 page, or to substitute an old or obsolete page with a new one with a different URL.
URLs can also be shortened by activating a shortening service that uses a redirect on a short-named domain. This is particularly useful in case of lengthy URLs containing many queries.
Tim Berners-Lee and the Internet Engineering Task Force working group is credited with developing the URL in 1994. It is formally specified in RFC 1738.