How do you work with environment variables in Golang?

Go provides built-in support for handling environment variables via the os package, enabling developers to read, set, and manage environment data securely and efficiently. To read a variable, use os.Getenv("KEY"), which returns an empty string if the key is not set, or combine os.LookupEnv("KEY") to distinguish between unset and empty values; for example, if value, exists := os.LookupEnv("DB_HOST"); exists checks whether the variable is explicitly set. Use os.Setenv("KEY", "value") to set a variable programmatically, os.Unsetenv("KEY") to remove it, and os.Environ() to retrieve all environment variables as a slice of "key=value" strings. Best practices include avoiding hardcoded values by externalizing configuration such as database credentials and API keys, validating required variables at startup using a loop with os.Getenv to ensure critical settings are present, and structuring configurations into config structs for better organization. For development, integrate libraries like github.com/joho/godotenv to load .env files using godotenv.Load(), which simplifies local setup without impacting production environments. However, avoid modifying environment variables in long-running or concurrent applications to prevent unintended side effects across goroutines. By combining Go’s simple os package functions with these practices, applications remain configurable, portable, and secure.

Working with environment variables in Go is straightforward using the os package, which provides functions to read, set, and manage environment variables at runtime.

Reading Environment Variables

To read an environment variable, use os.Getenv. It returns the value if the variable exists, or an empty string if it doesn't.

package main

import (
    "fmt"
    "os"
)

func main() {
    dbHost := os.Getenv("DB_HOST")
    fmt.Println("DB Host:", dbHost)
}

If the variable might not be set and you want a fallback, provide a default:

dbHost := os.Getenv("DB_HOST")
if dbHost == "" {
    dbHost = "localhost" // default value
}

Alternatively, use os.LookupEnv to check whether a variable is actually set (not just empty):

if value, exists := os.LookupEnv("DB_HOST"); exists {
    fmt.Println("DB_HOST is set to:", value)
} else {
    fmt.Println("DB_HOST is not set")
}

This is useful when an empty string is a valid value and you need to distinguish between unset and explicitly empty.

Setting Environment Variables

You can set environment variables programmatically using os.Setenv:

os.Setenv("API_KEY", "my-secret-key")

After setting, subsequent calls to os.Getenv("API_KEY") will return "my-secret-key".

Clearing or Unsetting Variables

Use os.Unsetenv to remove a variable:

os.Unsetenv("API_KEY")

Listing All Environment Variables

os.Environ() returns a slice of strings in the format "key=value", representing all current environment variables:

for _, env := range os.Environ() {
    fmt.Println(env)
}

Best Practices and Tips

• Don’t hardcode values: Use environment variables for configuration like database URLs, API keys, and feature flags.

• Validate required variables: At startup, check that essential variables are set:

  required := []string{"DB_HOST", "DB_USER", "DB_PASSWORD"}
  for _, key := range required {
      if os.Getenv(key) == "" {
          log.Fatalf("Missing required environment variable: %s", key)
      }
  }

• Use config structs and helpers: For larger apps, consider parsing env vars into a config struct, possibly with libraries like godotenv to load .env files in development:

  import "github.com/joho/godotenv"
  
  func loadEnv() {
      err := godotenv.Load()
      if err != nil {
          log.Println("No .env file found")
      }
  }

  This helps during local development without affecting production.

• Avoid mutating environment in long-running processes: Changes via Setenv/Unsetenv affect the entire process and may cause issues in concurrent scenarios.

Basically, Go gives you simple, reliable tools for environment variable handling—combine them with good practices to keep your app configurable and secure.

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