os: add os.devNull

Provides the platform-specific file path of the null device.

PR-URL: #38569
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

doc/api/os.md

@@ -122,6 +122,18 @@ The properties included on each object include:
 `nice` values are POSIX-only. On Windows, the `nice` values of all processors
 are always 0.
 
+## `os.devNull`
+<!-- YAML
+added: REPLACEME
+-->
+
+* {string}
+
+The platform-specific file path of the null device.
+
+* `\\.\nul` on Windows
+* `/dev/null` on POSIX
+
 ## `os.endianness()`
 <!-- YAML
 added: v0.9.4

lib/os.js

@@ -382,5 +382,12 @@ ObjectDefineProperties(module.exports, {
     enumerable: true,
     writable: false,
     value: isWindows ? '\r\n' : '\n'
+  },
+
+  devNull: {
+    configurable: true,
+    enumerable: true,
+    writable: false,
+    value: isWindows ? '\\\\.\\nul' : '/dev/null'
   }
 });

test/parallel/test-os.js

@@ -257,3 +257,10 @@ if (!common.isIBMi) {
 
 is.number(+os.freemem, 'freemem');
 is.number(os.freemem(), 'freemem');
+
+const devNull = os.devNull;
+if (common.isWindows) {
+  assert.strictEqual(devNull, '\\\\.\\nul');
+} else {
+  assert.strictEqual(devNull, '/dev/null');
+}