How to do it…

1. Open the console and create the folder chapter01/recipe04.
2. Navigate to the directory.

1. Create the get.go file with the following content:

        package main

        import (
          "log"
          "os"
        )

        func main() {
          connStr := os.Getenv("DB_CONN")
          log.Printf("Connection string: %s\n", connStr)
        }

1. Execute the code by calling DB_CONN=db:/user@example && go run get.go in the Terminal.
2. See the output in the Terminal:

1. Create the lookup.go file with the following content:

        package main

        import (
          "log"
          "os"
        )

        func main() {

          key := "DB_CONN"
    
          connStr, ex := os.LookupEnv(key)
          if !ex {
            log.Printf("The env variable %s is not set.\n", key)
          }
          fmt.Println(connStr)
        }

1. Execute the code by calling unset DB_CONN && go run lookup.go in the Terminal.
2. See the output in the Terminal:

1. Create the main.go file with the following content:

        package main
        import (
          "log"
          "os"
        )

        func main() {

          key := "DB_CONN"
          // Set the environmental variable.
          os.Setenv(key, "postgres://as:as@example.com/pg?
                          sslmode=verify-full")
          val := GetEnvDefault(key, "postgres://as:as@localhost/pg?
                                     sslmode=verify-full")
          log.Println("The value is :" + val)

          os.Unsetenv(key)
          val = GetEnvDefault(key, "postgres://as:as@127.0.0.1/pg?
                                    sslmode=verify-full")
          log.Println("The default value is :" + val)

        }
 
        func GetEnvDefault(key, defVal string) string {
          val, ex := os.LookupEnv(key)
          if !ex {
            return defVal
          }
          return val
        }

1. Run the code by executing go run main.go.
2. See the output in the Terminal: