htaccess to redirect url

Can I use htaccess to redirect url such as :
URL to
URL ?

# http://www.mydomain.com/.htaccess

RewriteEngine on
# If you have access to httpd.conf, enable this line (you can't use RewriteMap in .htaccess)
# If that's the case, of course, copy all lines here to within <Directory "/path/to/docroot">
# RewriteMap lc int:tolower
# Do not redirect if server_name doesn't contain .mydomain.com, use this to work with vhost
RewriteCond %{SERVER_NAME} !\.mydomain\.com$ [NC]
RewriteRule ^(.+) - [L]
# Do not redirect if server_name is already www.mydomain.com
# Say a request of http://www.mydomain.com/username/blah.html, then no redirection is needed
RewriteCond %{SERVER_NAME} ^www\.mydomain\.com$ [NC]
RewriteRule ^(.+) - [L]
# Else, if server_name is anything.mydomain.com
RewriteCond %{SERVER_NAME} ^[^.]+\.mydomain\.com$ [NC]
# Take the server_name env to the next rule
RewriteRule ^(.+) %{SERVER_NAME}=$1 [C]
# If RewriteMap above is enabled, comment out the following line
# What this line does is to map http://USERNAME.mydomain.com/ to http://www.mydomain.com/username/
# That's converting Uppercase Username to lowercase
# RewriteRule ^(.*)=(.*) ${lc:$1}$2 [C]
# ^([^.+) is the username
# (.*) is the / or anything requested, this is also called request_uri
# $1 is the value of username
# $2 is the value of request_uri including the slash /
RewriteRule ^([^.]+)\.mydomain\.com(.*) http://www.mydomain.com/$1$2 [R,L]

Once again, any codes I post here is untested (just wrote this up from scratch), so please followup this thread whether it works for you or not.

Dear freebsd,

I added the above lines to my httpds.conf, and now it looks like this : ( offcourse i changed the mydomain with my domain name),
<Directory "/usr/local/plesk/apache/vhosts">
Options Indexes FollowSymLinks
AllowOverride All
Order allow,deny
Allow from all
RewriteEngine on
RewriteCond %{SERVER_NAME} !\.mydomain\.com$ [NC]
RewriteRule ^(.+) - [L]
RewriteCond %{SERVER_NAME} ^www\.mydomain\.com$ [NC]
RewriteRule ^(.+) - [L]
RewriteCond %{SERVER_NAME} ^[^.]+\.mydomain\.com$ [NC]
RewriteRule ^(.+) %{SERVER_NAME}=$1 [C]
RewriteRule ^([^.]+)\.mydomain\.com(.*) URL$1$2 [R,L]
</Directory>
but i doesn't work as i expected.
Could you tell me what possibly be the problem?
Thank You.

Vera.

1) As I said, put those with <Directory "/path/to/docroot">. Are you sure /usr/local/plesk/apache/vhosts is your docroot? Check your httpd.conf and find the line DocumentRoot blahblahblah. The blahblahblah is the path of your docroot.
2) Say your docroot (DocumentRoot is /usr/local/plesk/apache, there must not be a subdir at
/usr/local/plesk/apache/no_subdir_here/username

Since you haven't provided any details of the problem, I suggest you to try to solve the problem yourself by adding:

RewriteEngine on
RewriteLog "/var/log/rewrite.log" # add this line, create this file manually before restarting apache
RewriteLogLevel 9 # add this line
RewriteCond %{SERVER_NAME} !\.mydomain\.com$ [NC]
..
..