not sure if i'm reading a shell script properly ... here's a script for downloading and installing kubernetes: https://get.kubernetes.io/ but it seems to be doing strange (messy) things with parameter substitution. first, there's this bit of weirdness partway through the script: if [[ -x ./cluster/get-kube-binaries.sh ]]; then # Make sure to use the same download URL in get-kube-binaries.sh KUBERNETES_RELEASE_URL="${KUBERNETES_RELEASE_URL}" \ ./cluster/get-kube-binaries.sh fi i'm unsure of the value of assigning a variable to itself; is there something subtle or tricky about that assignment that isn't obvious? then there are a number of constructs like this: if [[ -n "${KUBERNETES_SKIP_CREATE_CLUSTER-}" ]]; then exit 0 fi AIUI, the whole point of the construct ${VAR-default} is if VAR is not set, then the value of "default" will be used. so what does it mean to say: ${VAR-} that is, to have the empty string as the default value? is this some magic that i am unaware of? and there's this near the top: KUBERNETES_RELEASE_URL="${KUBERNETES_RELEASE_URL:-https://dl.k8s.io}"; ok, that will admittedly set that variable to a value if it does not already have a value, but i've always done that this way: : ${VAR:=defaultvalue} the script clearly works, but it seems to have been written by someone who didn't quite grasp proper parameter substitution. thoughts? rday