How to create a Django superuser if it doesn't exist non-interactively?

I want to automate creation of Django users via a Bash script. I found this snippet which almost suits my needs:

echo "from django.contrib.auth.models import User; User.objects.create_superuser('admin', 'admin@example.com', 'pass')" |\
    python manage.py shell

How can I modify it so that it's a nop if the user already exists?

Using manage.py shell

You can use the QuerySet API methods to check if a user exists, and then create it if it doesn't. Also, it may be easier to put the code in a heredoc:

cat <<EOF | python manage.py shell
from django.contrib.auth import get_user_model

User = get_user_model()  # get the currently active user model,

User.objects.filter(username='admin').exists() or \
    User.objects.create_superuser('admin', 'admin@example.com', 'pass')
EOF

Using a custom management command

Another, more maintainable option is to add a custom management command for your Django app. Adapting the example from the docs, edit yourapp/management/commands/ensure_adminuser.py to look like this:

import os
from django.contrib.auth import get_user_model
from django.core.management.base import BaseCommand

class Command(BaseCommand):
    help = "Creates an admin user non-interactively if it doesn't exist"

    def add_arguments(self, parser):
        parser.add_argument('--username', help="Admin's username")
        parser.add_argument('--email', help="Admin's email")
        parser.add_argument('--password', help="Admin's password")
        parser.add_argument('--no-input', help="Read options from the environment",
                            action='store_true')

    def handle(self, *args, **options):
        User = get_user_model()

        if options['no_input']:
            options['username'] = os.environ['DJANGO_SUPERUSER_USERNAME']
            options['email'] = os.environ['DJANGO_SUPERUSER_EMAIL']
            options['password'] = os.environ['DJANGO_SUPERUSER_PASSWORD']

        if not User.objects.filter(username=options['username']).exists():
            User.objects.create_superuser(username=options['username'],
                                          email=options['email'],
                                          password=options['password'])

Then you can call the new custom command from your Bash script like this:

python manage.py ensure_adminuser --username=admin \
    --email=admin@example.com \
    --password=pass