BASH: assign CLI positional argument to local variables

shell-can-take-three-arguments.sh

#!/bin/bash

### assign variables from CLI (posibional arguments)
first_user_arg="$1"
second_user_arg="$2"
third_user_arg="$3"

### have a default value to fallback on:
first_user_arg=${first_user_arg:-"default 1st value"}

### check if IS set:
if [[ -n "$second_user_arg" ]]; then
  echo "Received $second_user_arg as the 2nd argument."
else
  # fallback when $second_user_arg is not set
  second_user_arg=${second_user_arg:-"default 2nd value"}
fi

### check if NOT exists:
if [[ -z $third_user_arg ]]; then
  # echo "Defaulting to fallback for 3rd arg"
  third_user_arg=("default 3rd value")
fi

### using variables
echo "The variables:
1st var: $first_user_arg
2nd var: $second_user_arg
3rd var: $third_user_arg
done."