Environment Variables
export MQTT_HOSTNAME=...
export MQTT_USERNAME=...
export MQTT_PASSWORD=...
export MQTT_PORT=...
export DEVICE_ID=...
export HEART_RATE_ADAPTER_NAME=...
export HEART_RATE_ALIAS_PREFIX=...
export CADENCE_ADAPTER_NAME=...
export CADENCE_ALIAS_PREFIX=...
export FAN_ADAPTER_NAME=...
export FAN_ALIAS_PREFIX=...
export KICKR_MAC_ADDRESS=...
A partial and redacted sample of the .env file
To make sensitive information accessible but not displayed on the public repo, a .env file has been created in the home directory of the Raspberry Pi. This file's variables can be loaded by bash scripts then either parsed by the loading bash script to a python or other program, or the program can access it directly from the environment variables.
Variables
Some vairables of interest include:
| Variable | Description |
|---|---|
DEVICE_ID | ID of the Smartbike - used in MQTT topics |
MQTT_HOSTNAME | MQTT broker host address |
MQTT_PORT | MQTT broker port |
MQTT_USERNAME | Configured MQTT username |
MQTT_PASSWORD | Configured MQTT password |
KICKR_MAC_ADDRESS | KICKR smart trainer MAC address used by driver to connect via BLE |
HEART_RATE_ALIAS_PREFIX | BLE advertised name of the TICKR heart rate monitor - used by driver to connect via BLE |
CADENCE_ALIAS_PREFIX | BLE advertised name of the Wahoo cadence sensor - used by driver to connect via BLE |
FAN_ALIAS_PREFIX | BLE advertised name of the Wahoo headwind fan - used by driver to connect via BLE |
HEART_RATE_ADAPTER_NAME | Adapter address of the Raspberry Pi's BLE adapter - used by drivers to connect via BLE - the same value for FAN_ADAPTER_NAME & CADENCE_ADAPTER_NAME |
Adding, Removing, & Editing Variables
To modify the .env file open the .env file in the home directory using nano:
nano .env
Loading using bash script
To load the environment variables using a bash script add the following:
# at top of script
source ~/.env
...
# print value
echo $DEVICE_ID
# use as a string
echo "Smartbike ID: ${DEVICE_ID}"
Passing to python using bash script
To parse the variable to a python program, the python program must include the python shebang at the top of the file and configure an ArgumentParser using the argparse module:
#!/usr/bin/env python3
import os
from argparse import ArgumentParser
...
# initialise parser
parser = ArgumentParser()
parser.add_argument('--device_id', dest='device_id', type=str, help="Smartbike unique id", default=os.getenv('DEVICE_ID'))
# load parsed arguments
args = parser.parse_args()
...
# use argument
print(f'Smartbike ID: {args.device_id}')
To parse the variables from the bash script to the python program - indicate the variable and values when instigating the python program parsing the variables as string:
source ~/.env
...
python3 ~/iot/Drivers/my-driver/driver.py --device_id ${DEVICE_ID}
Order of parsed named arguments does not matter.
Loading without parsing in python
To load the variables without parsing explicitly from the bash script. Load the variables normally in the bash script and instigate the python program:
source ~/.env
...
python3 ~/iot/Drivers/my-driver/driver.py
In the python program use the os module to load the environment variables directly:
#!/usr/bin/env python3
import os
...
device_id = os.getenv('DEVICE_ID')