What does envconfig.Process() do

I'm looking through some source code using the envconfig library and am having trouble understanding what the below code does. I know it loads the environment variables but would like to understand what each specific line does. I was hoping somebody might be able to explain it to me. In particular what the line envconfig.Process("", &Env) does

 package config  
    import (
    	"html/template"
    	"log"
    	"os"
    
    	"github.com/joho/godotenv"
    	"github.com/kelseyhightower/envconfig"
    )
    
    type envVars struct {
    	Dbhost     string `required:"true" envconfig:"DB_HOST"`
    	Dbport     string `required:"true" envconfig:"DB_PORT"`
    	Dbuser     string `required:"true" envconfig:"DB_USER"`
    	Dbpassword string `required:"true" envconfig:"DB_PASS"`
    	Dbname     string `required:"true" envconfig:"DB_NAME"`
    	JwtKey     string `required:"true" envconfig:"JWT_KEY"`
    	HashKey    string `required:"true" envconfig:"HASH_KEY"`
    }
    
    //Env holds application config variables
    var Env envVars
    
    // Tpl template
    var Tpl *template.Template
    
    func init() {
    
    	wd, err := os.Getwd() //get path of working directory(current directory) - directory of this project
    	if err != nil {
    		log.Println(err, "::Unable to get paths")
    	}
    
    	Tpl = template.Must(template.ParseGlob(wd + "/internal/views/*.html")) //could use path.join in case it's used on linux instead of windows.
    
    	
    	//load .env file
    	err = godotenv.Load(wd + "/./.env") //loads environment variable file so that env variables can be accessed in code eg. by using os.GetEnv("DB_DIALECT"), won't work otherwise.
    
    	if err != nil {
    		log.Println("Error loading .env file, falling back to cli passed env")
    	}
    
    	err = envconfig.Process("", &Env)
    
    	if err != nil {
    		log.Fatalln("Error loading environment variables", err)
    	}
    
    }

envconfig.Process() populates a given struct with values pulled from environment variables. Which environment variables are used can be specified with the envconfig struct tag.

For example:

Dbhost     string `required:"true" envconfig:"DB_HOST"`

The above will populate the Dbhost field with the value of the DB_HOST environment variable. If the required tag is set to true, Process will return an error if no matching environment variable exists.

You can use the default tag if you want to define defaults for the case where a matching environment variable does not exist:

Dbhost     string `default:"host1" envconfig:"DB_HOST"`

The first parameter to Process is a prefix in order to only match environment variables with a certain prefix.

For example:

envconfig.Process("DB", &env)

The above will only consider environment variables with a DB_ prefix, e.g. DB_HOST, DB_PORT, DB_USER, etc. In your particular case, this would leave the fields JwtKey and HashKey unpopulated as the corresponding environment variables don't have a DB_ prefix.

I would suggest reviewing the README documentation on Github which provides some more detailed explanation and examples.