How it works…

The environment variables are accessed by the Getenv and Setenv functions  in the os package. The names of the functions are self-explanatory and do not need any further description. 

There is one more useful function in the os package. The LookupEnv function provides two values as a result; the value of the variable, and the boolean value which defines if the variable was set or not in the environment.

The disadvantage of the os.Getenv function is that it returns an empty string, even in cases where the environment variable is not set.

This handicap could be overcome by the os.LookupEnv function, which returns the string as a value of the environment variable and the boolean value that indicates whether the variable was set or not.

 To implement the retrieval of the environment variable or the default one, use the os.LookupEnv function. Simply, if the variable is not set, which means that the second returned value is false, then the default value is returned. The use of the function is part of step 9.