Redirecting the main domain to an existing WordPress install

RewriteEngine on

## Change "example.com" to your own domain name:
RewriteCond %{HTTP_HOST} ^(www.)?example.com$

## Change "directory" to the directory where WordPress is installed:
RewriteCond %{REQUEST_URI}!^/directory/

RewriteCond %{REQUEST_FILENAME}!-f
RewriteCond %{REQUEST_FILENAME}!-d

## Change "directory" to the directory where WordPress is installed:
RewriteRule ^(.*)$ /directory/$1

## Change "example.com" to your own domain name:
RewriteCond %{HTTP_HOST} ^(www.)?example.com$

## Change "directory" to the directory where WordPress is installed:
RewriteRule ^(/)?$ directory/index.php [L]