• Rust

let foo = env::var("FOO").unwrap_or("none".to_string());

• Rust

let foo = match env::var("FOO") {
    Ok(val) => val,
    Err(_e) => "none".to_string(),
};

• Rust

if let Ok(tnt_root) = env::var("TNT_ROOT") {
     //
}

• Rust

let foo = match env::var("FOO") {
    Ok(val) => val,
    Err(_e) => "none".to_string(),
};

• Ada

Foo : constant String :=
      Ada.Environment_Variables.Value (Name    => "FOO",
                                       Default => "none");

• C

const char * foo = getenv("FOO");
if (foo == NULL) foo = "none";

• Clojure

(def foo
  (or (System/getenv "FOO") "none"))

• C++

const char* tmp = std::getenv("FOO");
std::string foo = tmp ? std::string(tmp) : "none";

• C#

string foo = Environment.GetEnvironmentVariable("FOO");
if (string.IsNullOrEmpty(foo)) foo = "none";

• D

string foo = environment.get("FOO", "none");

• Dart

var foo = Platform.environment["FOO"] ?? "none";

• Elixir

foo = System.get_env("FOO", "none")

• Erlang

Foo = os:getenv("FOO","none").

• Fortran

  call get_environment_variable ("FOO", length=n, status=st)
  if (st /= 0) then
    foo = "none"
  else
    allocate (character(len=n) :: foo)
    call get_environment_variable ("FOO", value=foo)
  end if 

• Go

foo := os.Getenv("FOO")
if foo == "" {
	foo = "none"
}

• Go

foo := cmp.Or(os.Getenv("FOO"), "none")

• Go

foo, ok := os.LookupEnv("FOO")
if !ok {
	foo = "none"
}

• Groovy

def foo = System.getenv('FOO') ?: 'none'

• Haskell

do
  foo <- catch (getEnv "FOO") (const $ pure "none" :: IOException -> IO String)
  -- do something with foo

• JS

const foo = process.env.FOO ?? 'none'

• JS

const foo = process.env["FOO"] || "none";

• Java

String foo = System.getenv("foo");
if (foo == null) {
	foo = "none";
}

• Java

String foo;
try {
    foo = getenv("FOO");
    if (foo == null) throw new Exception();
} catch (Exception e) {
    foo = "none";
}

• Kotlin

val foo = System.getenv("FOO") ?: "none"

• Lisp

(defvar foo
(uiop:getenv "FOO")
"The contents of environment variable FOO.")

• Lua

foo = os.getenv("FOO") or "none"

• PHP

$foo = getenv("FOO") ?: "none";

• Pascal

var
  foo: string;
begin
  foo := GetEnvironmentVariable('FOO');
  if (foo = '') then foo := 'none';
end.

• Perl

my $foo = $ENV{FOO} // 'none';

• Python

foo = os.environ.get('FOO', 'none')

• Python

try:
    foo = os.environ['FOO']
except KeyError:
    foo = "none"

• Python

foo = getenv('FOO', 'none')

• Ruby

foo = ENV["FOO"]

• Scala

val foo = sys.env.getOrElse("FOO", "none")

• Smalltalk

| foo |
foo := CEnvironment getUserEnvironment at: 'FOO' ifAbsent: [ 'none' ].

• VB

foo = IIf(Environ("FOO") = "", "none", Environ("FOO"))

• VB

Dim _foo as String
Try
	foo = Environment.GetEnvironmentVariable("FOO")
Catch ex as Exception
	foo = "none"
End Try