Pre-tip: When using search and replace in Vim, you don't need to use slashes This works just fine:
%s#search#replace
Did you know $replace doesn't have to be a literal expression? You can also use Vim functions! For example:
%s#bar#\=line('.')
will replace every occurrence of 'bar' for its line number. You can get creative and use any other Vimscript function.