Using --user-data with doctl

I am trying to understand the --user-data flag in the doctl computer docker create command. It’s referenced here:

https://docs.digitalocean.com/reference/doctl/reference/compute/droplet/create/

I thought that something like this might work.

doctl compute droplet create \
    --verbose \
    --wait \
    --image docker-20-04 \
    --size c-2 \
    --region sfo3 \
    --user-data "#!/bin/bash\ndocker pull hello-world;" \
    alpha-engine

But it doesn’t seem to work.

However, if I make a file (e.g. “hello.sh”) with contents

#!/bin/bash
docker pull hello-world

And then execute

doctl compute droplet create \
    --verbose \
    --wait \
    --image docker-20-04 \
    --size c-2 \
    --region sfo3 \
    --user-data-file hello.sh
    alpha-engine

It seems to work.

I can’t really find much help on this topic but I appreciate any help I can get. I’d really like to understand the --user-data flag. I’ve tried variations (e.g. not including the #!/bin/bash\n) but haven’t found anything that works yet.