Help with cloud init syntax for runcmd

The documentation is a bit lacking, but from the comments on the example in the upstream docs you learn:

# runcmd contains a list of either lists or a string
# each item will be executed in order at rc.local like level with
# output to the console
# - if the item is a list, the items will be properly executed as if
#   passed to execve(3) (with the first arg as the command).
# - if the item is a string, it will be simply written to the file and
#   will be interpreted by 'sh'
#
# Note, that the list has to be proper yaml, so you have to escape
# any characters yaml would eat (':' can be problematic)

So wrapping everything in single quotes seems like it should do the trick:

#cloud-config
runcmd:
 - '\curl -sSL https://get.rvm.io | bash -s stable'

The resulting script can be found for debugging purposes in /var/lib/cloud/instance/scripts/runcmd