Is there a way to add IF to .htaccess? - .htaccess

Question

I'm building a web-builder, but I have no idea how to use .htaccess. Is there a way to make something like that (I'll write it in php because my English bad so it is easier to me):
<?php
if(ERROR && ONE_NAME){ //There is no page like that, for example: www.example.com/thispageisntexists
//redirect to page /website.php?webname=thispageisntexists
}elseif(ERROR && TWO_OR_MORE){ //for example: www.example.com/thispageisntexists/hi.php
//redirect to page /website.php?webname=thispageisntexists&pagename=hi
//if url is www.example.com/thispageisntexists/hi.php#hi rediract to /website.php?webname=thispageisntexists&pagename=hi#hi
//if url is www.example.com/thispageisntexists/hi.php?name=vlad&last=gincher rediract to /website.php?webname=thispageisntexists&pagename=hi$name=vlad&last=gincher
//and so on...
}
?>
inside website.php I'll check if the page exist and if no it will redirect to 404.php, and if it exist it will show the website.

Answer 1

I find it somewhat unclear what url's should be redirected or rewritten. I am assuming you have (or want) seo urls like this http://example.com/aaa and http://example.com/aaa/bbb and want to internally rewrite that to something that makes sense to the server.
You want it to work if there is already a query string present. This means that you have to concat the two query strings with the [QSA] flag.
"There is no page like that" translates to a condition that checks if the requested filename exists. You can negate that condition with a ! before the second argument. That would be RewriteCond %{REQUEST_FILENAME} !-f.
#hi is an anchor. It is never sent to the server. Your browser should however automatically keep appending that to the url, even when redirecting the request.
I see that Jon Lin already posted a .htaccess file that should work for you. I will still post this answer to clarify what is used there.

Answer 2

Try:
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !^/website\.php
RewriteRule ^([^/]+)$ /website.php?webname=$1 [L,R,QSA]
# you can remove the "R" if you don't want to redirect the browser
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !^/website\.php
RewriteRule ^([^/]+)/(.*?)(\.php)?$ /website.php?webname=$1&pagename=$2 [L,R,QSA]
# you can remove the "R" if you don't want to redirect the browser

Answer 3

There's nothing with such an explicit IF-THEN-ELSE. .htaccess does have ways of doing conditional URL/URI redirects and rewrites, using RewriteCond and RewriteRule commands. They use "regular expressions" to match patterns, so they aren't as flexible as a real scripting language like PHP, but you can do lots with them.
RewriteEngine On
RewriteCond %{REQUEST_FILE} !-f
RewriteRule /?(.*)$ /website.php?webname=$1 [L]
might be a start for what I understand you're trying to do.