Setting global variable to rewrite some url - .htacess

[aqwxsz]

Perhaps it will appear quite easy but I have an issue with my .htaccess. I want to rewrite my url such that \[code\]<a href="http://stackoverflow.com/admin">some text</a>\[/code\] can be rewritten as \[code\]<a href=""http://localhost:8888/madison/the-madison-project/admin/index">some text</a>\[/code\]So I set this : \[code\]SetEnv root:/madison/the-madison-project/RewriteRule ^admin[/]?$ {%ENV:root}admin/index\[/code\]But it doesn't work. How can I fix it?