How to properly create relative links - php

Question

in my source code, this a button link like this:
then the web page's code is like this:
but when click the button, the url is:
http://localhost/personal/applications/mywebtest/install/?step=2
why "/personal/applications" is added in?

Answer 1

Edit: Let me start with...
How the href attribute works
Let's say, you are on a page http://example.com/foo/bar.html and you have a hyperlink there, it can be one of the three:
path/newpage.html - this is a relative path (no slash in front), which means it will take you to http://example.com/foo/path/newpage.html
/path/newpage.html - this is an absolute path (starts with a slash), which will take you to http://example.com/path/newpage.html
example.com/otherpage.html - this is still a relative path (as in the first example), it will take you to http://example.com/example.com/otherpage.html *
this is because the browser don't know if you mean domain example.com or directory with a dot in it example.com, so it's a standard to treat it as a directory.
http://example.com/path/newpage.html - this is an absolute URL (it starts with a protocol) - the browser don't need to do any guessing here, can take you straight to http://example.com/path/newpage.html
(this is assuming that the base is not set, please read rest of the answer or take a look at https://www.w3schools.com/tags/tag_base.asp)
Now the original answer
When you use relative links (links without domain name) in the <a> elements your browser needs a whole URL (with domain name) to fulfill such request when you click the link. So it takes the current protocol (http) and domain localhost and glues it with $_SERVER['PHP_SELF'] which is
The filename of the currently executing script, relative to the
document root. For instance, $_SERVER['PHP_SELF'] in a script at the
address http://example.com/foo/bar.php would be /foo/bar.php.
(https://secure.php.net/manual/en/reserved.variables.server.php)
So you can either create full urls for the href as suggested here https://stackoverflow.com/a/46359685/299774
href=<?php echo $_SERVER['HTTP_HOST']."/mywebtest/install"; ?>?step=2';"
But this can cause problems in case you want to save such HTML in the DB (for example it is a post in your blog) - then moving your app to a different domain would require changing contents in the DB and fill it with new domain.
So I would stick to relative values in href, you can accomplish that by setting base meta tag in your HTML: https://stackoverflow.com/a/6848509/299774
or by utilizing mod_rewrite or similar tool four your server, but it has been long since I was doing it + outside of scope of this question, but you can check popular frameworks (CakePHP, Laravel) how they do it.
(And they have to do it, because being able to move app between domains is a must: local testing, staging, production)

Answer 2

That's because PHP_SELF returns the path on disk to the current file. PHP itself is unaware of where/how the page is served. You will have to find another variable/strategy for your link. Also, if you really want to link to the same page, you could just use ?step=2.

Answer 3

you can use of $_SERVER['HTTP_HOST']
<input type="button" name="step" value="Continue to step 2 of 3"
onClick="location.href = '<?php echo (isset($_SERVER['HTTPS'])?"https" : "http")."://". $_SERVER['HTTP_HOST']."/mywebtest/install/"; ?>?step=2';"/>