If you want to redirect non-www url to www url , for both http and https use this ;
RewriteEngine on
RewriteCond %{HTTPS} off
RewriteCond %{HTTP_HOST} !^www\.(.*)$ [NC]
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L]
RewriteCond %{HTTPS} on
RewriteCond %{HTTP_HOST} !^www\.(.*)$ [NC]
RewriteRule ^(.*)$ https://www.%{HTTP_HOST}/$1 [R=301,L]
If you want to redirect www to non-www url use this ;
RewriteEngine On
RewriteCond %{HTTP_HOST} ^example\.com$ [NC]
RewriteRule ^(.*)$ http://www.example.com/$1 [R=301,L]
RewriteCond %{HTTPS_HOST} ^example\.com$ [NC]
RewriteRule ^(.*)$ https://www.example.com/$1 [R=301,L]
or without using domainname ;
RewriteEngine On
RewriteCond %{HTTP_HOST} ^www\.(.*) [NC]
RewriteRule ^(.*) http://%1/$1 [R=301,L]
RewriteCond %{HTTPS_HOST} ^www\.(.*) [NC]
RewriteRule ^(.*) https://%1/$1 [R=301,L]