Julia run external programm with environmental variables: Don't interpolate $ - julia

Question

I'm trying to run a shell command from Julia which needs to have an environment variable set to some specific value. I have two problems:
How to set environment variables to be used by Julia's
run(command, args...; wait::Bool = true) command?
How to pass special sign $ to this process without interpolating it? I want to test if the variable is available for my program.
What I have done so far:
Let's say I want to define an environment variable FOO=bar and check if it's accessible within the shell with shell command echo $FOO.
To prevent Julia interpolating $ I already quoted it like explained in the official documentation but then echo is printing $PATH and not its value.
So for FOO I got the following output
julia> run(`echo '$FOO'`)
$FOO
Process(`echo '$FOO'`, ProcessExited(0))
but would have expected something like
julia> run(`echo '$FOO'`)
Process(`echo '$FOO'`, ProcessExited(0))
if FOO is undefined or
julia> run(`echo '$FOO'`)
bar
Process(`echo '$FOO'`, ProcessExited(0))
if the value is set to bar.

Answer 1

Check out the Julia documentation on environment variables. You can set an environment variable with:
julia> ENV["FOO"] = "bar"
"bar"
and you can retrieve the value of an environment variable with:
julia> ENV["FOO"]
"bar"
julia> ENV["PATH"]
"really long string of my path"
As you've already stated, you can avoid interpreting the $ by single-quoting that part of your run command. I'm not totally sure what you are looking for there.

Answer 2

Not elegant, but this works:
julia> write("temp.sh", "echo foo=\$BAR");
julia> run(`bash temp.sh`)
foo=
Process(`bash temp.sh`, ProcessExited(0))
julia> ENV["BAR"] = "bar";
julia> run(`bash temp.sh`)
foo=bar
Process(`bash temp.sh`, ProcessExited(0))
I guess Julia injects the content of ENV into the shell before running the command. And that's all I needed to know as I'll be launching other executables which require some environment variables to be set. So when setting them inside ENV[], they will be available to the executables you run from within that Julia session.