Non-interactive install

[alexbowers]

I am trying to provision a Vagrant machine, but have ran into problems with the provision of Rustup, partially caused (I think), because it isn't non-interactive.

I have tried curl ... | sh -- -y, however that doesn't work either. What would be preferable would be a generated script that assumes non-interactive.

For example rustup-noninter.sh.

[hlzhang]

try curl https://sh.rustup.rs -sSf | sh -s -- -y