Configuring .htaccess for multiple domains and SSL - .htaccess

Question

I have a primary domain "example.co.uk" and 6 other domains + 1 IP address pointed to the same folder root.
I would like to use HTTPS for the primary domain i.e. https://www.example.co.uk and redirect all the other domains to the homepage of this domain (avoiding SEO issues and content duplication with the example.com domain and IP address)
How do I achieve this using my current .htaccess file?
RewriteEngine on
#Redirect IP address to example.co.uk.
RewriteCond %{HTTP_HOST} ^12\.34\.567\.890
RewriteRule (.*) https://www.example.co.uk/$1 [R=301,L]
# Redirect example.com to example.co.uk.
RewriteCond %{HTTP_HOST} ^(www\.)?example\.com$ [NC]
RewriteRule ^(.*)$ https://www.example.co.uk/$1 [R=301,L]
# Redirect example2.co.uk to example.co.uk.
RewriteCond %{HTTP_HOST} ^(www\.)?example2\.co\.uk$ [NC]
RewriteRule ^(.*)$ https://www.example.co.uk/$1 [R=301,L]
# Redirect example3.co.uk to example.co.uk.
RewriteCond %{HTTP_HOST} ^(www\.)?example3\.co\.uk$ [NC]
RewriteRule ^(.*)$ https://www.example.co.uk/$1 [R=301,L]
# Redirect example4.com to example.co.uk.
RewriteCond %{HTTP_HOST} ^(www\.)?example4\.com$ [NC]
RewriteRule ^(.*)$ https://www.example.co.uk/$1 [R=301,L]
# Redirect example5.co.uk to example.co.uk.
RewriteCond %{HTTP_HOST} ^(www\.)?example5\.co\.uk$ [NC]
RewriteRule ^(.*)$ https://www.example.co.uk/$1 [R=301,L]
# Redirect example6.com to example.co.uk.
RewriteCond %{HTTP_HOST} ^(www\.)?example6\.com$ [NC]
RewriteRule ^(.*)$ https://www.example.co.uk/$1 [R=301,L]

Answer 1

You can reduce the number of rules by negating the condition check against the HTTP HOST. Then, you'll just need the rule to check HTTPS:
RewriteEngine On
RewriteCond %{HTTP_HOST} ^(www\.)?example\.co\.uk$ [NC]
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://www.example.co.uk/$1 [L,R=301]
# redirect all the other domains to the homepage
RewriteCond %{HTTP_HOST} !^www\.example.co.uk$ [NC]
RewriteRule ^(.*)$ https://www.example.co.uk/ [L,R=301]
In your question, you said you wanted to redirect all the other domains to the homepage of this domain, but your rules aren't doing that at all. Your rules are redirecting the request to the same request but just this domain. If you want to keep that logic, then you need to add a $1 to the end of the https://www.example.co.uk/.