How to fix environment variable has empty value in Docker

# The warning looks like this:
# WARN[0000] The "DATABASE_URL" variable is not set. Defaulting to a blank string.

# Check if the variable exists in your environment
echo $DATABASE_URL

# Or check all environment variables
env | grep DATABASE_URL

# View what Docker Compose sees
docker-compose config

# Set and export the variable
export DATABASE_URL="postgres://user:pass@localhost:5432/mydb"

# Verify it's set
echo $DATABASE_URL

# Now run docker-compose
docker-compose up

# For bash (add to ~/.bashrc or ~/.bash_profile)
echo 'export DATABASE_URL="postgres://user:pass@localhost:5432/mydb"' >> ~/.bashrc
source ~/.bashrc

# For zsh (add to ~/.zshrc)
echo 'export DATABASE_URL="postgres://user:pass@localhost:5432/mydb"' >> ~/.zshrc
source ~/.zshrc

# Create .env file in your project root
cat > .env << 'EOF'
DATABASE_URL=postgres://user:pass@localhost:5432/mydb
REDIS_URL=redis://localhost:6379
API_KEY=your-api-key-here
NODE_ENV=development
EOF

# Show the resolved configuration
docker-compose config

# Or specify a different env file
docker-compose --env-file ./config/.env up

services:
  app:
    image: myapp
    environment:
      # Use :- for default when unset or empty
      - DATABASE_URL=${DATABASE_URL:-postgres://localhost:5432/dev}

      # Use - for default only when unset (allows empty values)
      - OPTIONAL_VAR=${OPTIONAL_VAR-default_value}

      # Require the variable (fail if not set)
      - REQUIRED_VAR=${REQUIRED_VAR:?Error: REQUIRED_VAR must be set}

# Problem: $ in password gets interpreted
PASSWORD="p@ss$word123"  # $word gets expanded to empty string

# In .env file (values aren't typically quoted, but this varies)
PASSWORD=p@ss$word123

# Or if your version supports it:
PASSWORD='p@ss$word123'

services:
  app:
    environment:
      # Use $$ to escape a literal $ sign
      - PASSWORD=p@ss$$word123

export PASSWORD='p@ss$word123'

# This loses your environment variables
sudo docker-compose up  # Variables not available!

# Option 1: Use -E to preserve environment
sudo -E docker-compose up

# Option 2: Pass variables explicitly
sudo DATABASE_URL="$DATABASE_URL" docker-compose up

# Option 3: Add yourself to docker group (recommended)
sudo usermod -aG docker $USER
# Log out and back in, then:
docker-compose up  # No sudo needed!

# Show the fully resolved configuration
docker-compose config

# Check which variables are resolved
docker-compose config | grep -A5 environment

# Verbose output for debugging (Compose V2)
docker compose config --environment