sed script not executing in a Vagrantfile - sed

Question

I can't for the life of me get sed working with vagrant provisioning. I want to make a inline change to /etc/hosts.
I've verified that the sed command works when run in the shell.
Here is my Vagrantfile:
# vi: set ft=ruby :
########### Global Config ###########
machines = ["admin2"]
num_hdd_per_osd = 3
vagrant_box = %q{bento/ubuntu-18.04}
#####################################
machines.each do |machine|
Vagrant.configure("2") do |config|
config.vm.define machine do |node| #name vagrant uses to reference this VM
node.vm.box = vagrant_box
node.vm.hostname = machine
node.vm.network "private_network", ip: "192.168.0.#{ machines.index(machine) + 10}"
node.vm.provider "virtualbox" do |vb|
# Display the VirtualBox GUI when booting the machine
vb.gui = false
vb.name = machine # name virtualbox uses to refer to this vm
# Customize the amount of memory on the VM:
vb.memory = "1048"
# Core Count
vb.cpus = "2"
end
if node.vm.hostname.include? "admin"
node.vm.provision "shell", inline: <<-SHELL
sed -i.bak -e 's,\\(127\\.0\\.0\\.1[[:space:]]*localhost\\),\\1aa,' /etc/hosts
SHELL
end
end
end
end
I should see /etc/hosts changed to 127.0.0.1 localhostaa but it is unchanged.
What is wrong?
EDIT: I updated the code with the suggestion from Alex below. It now uses inline: <<-SHELL and escaped ALL escapes (so double escape). It Works!

Answer 1

The problem there is your Vagrantfile is Ruby code, and your sed script is inside a Ruby here string.
If you try this simplified Ruby script:
# test.rb
puts <<-SHELL
sudo sed -i.bak -e 's,\(127\.0\.0\.1[[:space:]]*localhost\),\1aa,' /etc/host
SHELL
You may see the problem:
▶ ruby test.rb
sudo sed -i.bak -e 's,(127.0.0.1[[:space:]]*localhost),aa,' /etc/host
That is, the \1 and other \ have been interpreted by Ruby prior to interpolation in the here string.
The best option for you is to use the <<'SHELL' notation, similar to what you would do in Bash:
node.vm.provision "shell", inline: <<-'SHELL'
sed -i.bak -e 's,\(127\.0\.0\.1[[:space:]]*localhost\),\1aa,' /etc/hosts
SHELL
The other option would be to escape the backslash in \1. Also, note that, as far as I can tell, the call to sudo is not required there either.
If, however, you need to interpolate a string in this script, you could do something like this:
# test.rb
mystring = 'aa'
$script = "sed -i.bak -e '" +
's,\(127\.0\.0\.1[[:space:]]*localhost\),\1' + "#{mystring},' /etc/hosts"
And then in your provisioner:
node.vm.provision "shell", inline: $script
See also this related answer.