Add userHomeDir (denoland/deno_std#521)

Original: ff7fb5a5d6

os/README.md

@@ -0,0 +1,16 @@
+# os
+
+Module provide platform-independent interface to operating system functionality.
+
+## Usage
+
+### userHomeDir
+
+Returns the current user's home directory. On Unix, including macOS, it returns the \$HOME environment variable. On Windows, it returns %USERPROFILE%.
+Needs permissions to access env (--allow-env).
+
+```ts
+import { userHomeDir } from "https://deno.land/std/os/mod.ts";
+
+userHomeDir();
+```

os/mod.ts

@@ -0,0 +1,26 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+
+/**
+ * Returns the current user's home directory.
+ * On Unix, including macOS, it returns the $HOME environment variable.
+ * On Windows, it returns %USERPROFILE%.
+ * Needs permissions to access env (--allow-env).
+ *
+ * Ported from Go: https://github.com/golang/go/blob/go1.12.5/src/os/file.go#L389
+ */
+export function userHomeDir(): string {
+  let env = "HOME";
+  let envErr = "$HOME";
+
+  if (Deno.platform.os === "win") {
+    env = "USERPROFILE";
+    envErr = "%USERPROFILE%";
+  }
+
+  const value = Deno.env()[env];
+  if (value !== "") {
+    return value;
+  }
+
+  throw new Error(`Environment variable '${envErr}' is not defined.`);
+}

os/test.ts

@@ -0,0 +1,8 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+import { test } from "../testing/mod.ts";
+import { assertNotEquals } from "../testing/asserts.ts";
+import { userHomeDir } from "./mod.ts";
+
+test(function testUserHomeDir(): void {
+  assertNotEquals(userHomeDir(), "");
+});

test.ts

@@ -23,6 +23,7 @@ import "./textproto/test.ts";
 import "./util/test.ts";
 import "./ws/test.ts";
 import "./encoding/test.ts";
+import "./os/test.ts";
 
 import { xrun } from "./prettier/util.ts";
 import { red, green } from "./colors/mod.ts";