Automatic Proxy Configuration Pac File

Save it as a file and service it in an http / https server. Tools like FoxyProxy can use it.

function FindProxyForURL(url, host)
{
  // Direct connections to non-FQDN hosts
  if (isPlainHostName(host) ||
     (host == "127.0.0.1") ||
     (host == "*.xxx.com") ||
     (shExpMatch(host, "*.xxx.local")) ||
     (shExpMatch(host, "*.xxx.org")) ||
     (shExpMatch(host, "192.168.*"))) {
       return "DIRECT"
  } else {
    return "PROXY 192.168.1.12:3128"
  }
}