Tuesday, June 14, 2011

Apple DNS cache, and a bourne revelation [to me]

I learned a couple of interesting things today. The first is that Mac OS X, or at least some applications, cache DNS results. This is irritating, but fortunately there is a way to clear out the cache. Run the following command in a terminal to clear out the cache.

dscacheutil -flushcache

On the FreeBSD side of life, I had a minor revelation related to bourne (sh) scripting. I have occasionally wondered if it was possible to build the name of a variable dynamically. When I've wondered aloud, the answer I've received has always been that this is not possible. Today, I was reading through /etc/network.subr and I happened upon this bit of code.

if [ -n "${static_routes}" ]; then
for i in ${static_routes}; do
eval route_args=\$route_${i}
route add ${route_args}

Like a beam of light from Heaven, I suddenly realized that this little eval statement is the answer to my hopes. It allows you to build a variable name on the fly!