Unable to download buildkit on ubuntu
Discussed this a bit over Mattermost. For debugging this, it made sense to run the first half of the command and check the output, e.g.

curl -Ls https://civicrm.org/get-buildkit.sh


It should display a bash script. However, it actually displayed an error message about an IP restriction. A quick work-around was to download the script through a different URL, i.e.

curl https://raw.githubusercontent.com/civicrm/civicrm-buildkit/master/bin/civi-download-tools | bash -s -- --full --dir ~/buildkit