Redirect URL from subdirectory to sub domain using htaccess

We can redirect URL's from any subdirectory (like maindomain.com/dorectoryname) to a sub domain (subdomain.maindomain.com) using PHP and .htaccess by the subsequent ways.
For example, the .htaccess file is full of rules like the following:

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RewriteCond %{HTTP_HOST} ^(www\.)?maindomain\.com$

RewriteRule ^dorectoryname/(.*)$ http://subdomain.maindomain.com/$1 [L,QSA,R=301]

or we can using this code
 

RewriteCond %{REQUEST_URI} ^/dorectoryname

RewriteRule ^(.*)$ http://subdomain.maindomain.com/$1 [R=301,L,P]