It's often convenient to store a password in the macOS system keychain and retrieve it inside a shell script.
Here's the bash command for setting a password:
security add-generic-password -s "Keychain item name here" -a "username here"
Then enter your password when prompted.
After you run this once, you can retrieve the password in a script like this:
PASSWORD=`security find-generic-password -s "Keychain item name here" -a "username here" -w`
You can then use
$PASSWORD whenever you need the password in your script.