eval and substitute from prototype env file

dotenv.sh

#!/bin/bash

# Default values for source and output files
env_example=".env.example"
env_output=".env"

# Flag to ask for confirmation for each variable (enabled by default)
ask_each_var=1

# Function to display help message
display_help() {
    echo "Usage: $0 [OPTIONS]"
    echo
    echo "Options:"
    echo "  -h, --help      Show this help message and exit."
    echo "  -q, --quiet     Run without asking for confirmation for each variable."
    echo "  -s, --source    Specify the source file. Default is '.env.example'."
    echo "  -o, --output    Specify the output file. Default is '.env'."
    echo
    echo "This script processes a source environment file (.env.example by default),"
    echo "updating or adding its variables to a destination environment file (.env by default)."
    echo "It supports command substitution and environment variable expansion."
    echo
}

# Process script arguments
while [[ "$#" -gt 0 ]]; do
    case $1 in
        -h|--help)
            display_help
            exit 0
            ;;
        -q|--quiet)
            ask_each_var=0
            ;;
        -s|--source)
            env_example="$2"
            shift
            ;;
        -o|--output)
            env_output="$2"
            shift
            ;;
        *)
            echo "Unknown option: $1"
            display_help
            exit 1
            ;;
    esac
    shift
done

# Check if the source file exists
if [ ! -f "$env_example" ]; then
    echo "Source file $env_example does not exist."
    exit 1
fi

# Create the output file if it doesn't exist
if [ ! -f "$env_output" ]; then
    touch "$env_output"
fi

# Function to ask for confirmation, showing current and new values
ask_confirmation() {
    current_value=$2
    new_value=$3
    while true; do
        read -p "Variable '$1' has value '$current_value'. Replace with new value '$new_value'? [y/n] " yn < /dev/tty
        case $yn in
            [Yy]* ) return 0;;
            [Nn]* ) return 1;;
            * ) echo "Please answer yes or no.";;
        esac
    done
}

# Read current .env file into an associative array
declare -A env_vars
while IFS='=' read -r key value; do
    env_vars["$key"]="$value"
done < "$env_output"

# Process each line from .env.example
while IFS='=' read -r key value; do
    # Replace command substitution and environment variable expansion
    new_value=$(eval "echo $value")

    # Check if the key already exists in the destination file
    if [[ "${env_vars[$key]+isset}" ]]; then
        # Read the existing value from the destination file
        current_value="${env_vars[$key]}"

        # Check if we should ask for confirmation and if the values are different
        if [[ $ask_each_var -eq 1 && "$current_value" != "$new_value" ]]; then
            ask_confirmation "$key" "$current_value" "$new_value" && env_vars["$key"]="$new_value"
        else
            env_vars["$key"]="$new_value"
        fi
    else
        # If the key is not in the existing file, add it
        env_vars["$key"]="$new_value"
    fi
done < "$env_example"

# Write the .env file
> "$env_output"
for key in "${!env_vars[@]}"; do
    echo "$key=${env_vars[$key]}" >> "$env_output"
done

echo "Updated .env file:"
cat "$env_output"