vcl_cookie_test.rb

regex = /regsuball\(req\.http\.Cookie, \"(.*)\", \"(.*)\"\)/

vcl = %Q{
	if (req.http.Cookie) {
	    set req.http.Cookie = ";" + req.http.Cookie;
	    set req.http.Cookie = regsuball(req.http.Cookie, "; +", ";");
	    set req.http.Cookie = regsuball(req.http.Cookie, ";(user_id|t)=", "; $1=");
	    set req.http.Cookie = regsuball(req.http.Cookie, ";[^ ][^;]*", "");
	    set req.http.Cookie = regsuball(req.http.Cookie, "^[; ]+|[; ]+$", "");

	    if (req.http.Cookie == "") {
	        remove req.http.Cookie;
	    }
	}	
}

$operations = []
vcl.gsub(regex) do # surely a better way to do this... how do i .map a regex?	
	$operations << { regex: $1.strip, replace: $2.strip }
end

def mangle_cookie(cookie)
	puts " ---- "
	puts " #{cookie}"
	puts " ---- "
	cookie = ";"+cookie # this is from the first part of the VCL: 'set req.http.Cookie = ";" + req.http.Cookie;'
	$operations.each do |operation|
		puts "About to run: #{operation.inspect}"
		re = Regexp.new(operation[:regex])
		cookie = cookie.gsub(re) do
			(operation[:replace] || '').gsub("$1", $1.to_s)
		end
		puts "Now the cookie is: #{cookie}\n\n"		
	end

	if cookie == ""
		puts "EMPTY -- publicly cacheable"
	else
		puts "NOT empty -- cannot cache"
	end
end

mangle_cookie "__utma=21179093278093.141XX4029191.12; __utmz=211798.1412636099.7.2.utmcsr=themarshallproject.org|utmccn=(referral)|utmcmd=referral|utmcct=/; t=IjE0MTQxMTA2MjZ8cHxRRmQyOalQ4aWhOMnh4NUtsRWx6NmhNPSI%3D--bdce16d703d2c3561; user_id=X--29da97db4fac7411; _endrun_session=YWGoxVkcyRXloczNBUEJlNXVLcVNkt1dGc9PQ%3D%3D--59f7500df713b4c471; _ga=GA1.2.193.14565; _gat=1"
mangle_cookie "__utma=2117908093.14140XXXXXX29191.12; __utmz=211798.1412636099.7.2.utmcsr=themarshallproject.org|utmccn=(referral)|utmcmd=referral|utmcct=/; _endrun_session=c2FRdjBra2ZNUinU2VjFOWFl; _ga=GA1.2.1493278093.1408905565; _gat=1"

The VCL comes from: https://www.varnish-cache.org/trac/wiki/VCLExampleRemovingSomeCookies#RemovingallBUTsomecookies