source not found for source $(pipenv --venv)/bin/activate - bash

Question

I'm trying to learn how to use pipenv, and while I can start it and use it from the shell, I can't work out how to open in from a script, the tutorial I am using says to write the following file:
#!/bin/sh
export FLASK_APP=./myapp/index.py
source $(pipenv --venv)/bin/activate
flask run -h 0.0.0.0
as a shell script, but I get the following error:
./bootstrap.sh: 5: source: not found
* Serving Flask app "./catalogueService/index.py"
* Environment: production
WARNING: This is a development server. Do not use it in a production deployment.
Use a production WSGI server instead.
* Debug mode: off
Usage: flask run [OPTIONS]
Error: Could not import "index".
The could not import index, is fine, I can work with that, what I don't know is what:
source $(pipenv --venv)/bin/activate
Does, and what it should really be so it can find pipenv, I installed it using pip the usual way. Why is it not finding it please

Answer 1

On Linux or macOS:
source "$(pipenv --venv)/bin/activate"
On Windows:
source "$(pipenv --venv)/Scripts/activate"
OR
activate(){
activate_file=$(pipenv --venv)/bin/activate
if [ -e "$activate_file" ]; then
. $activate_file
# the pipenv shell normally enables these as well
export PYTHONDONTWRITEBYTECODE=1
export PIPENV_ACTIVE=1
if [ -f "${VIRTUAL_ENV}/.project" ]; then
cd $(cat "${VIRTUAL_ENV}/.project")
fi
return
fi
}