lib: allow custom names for spawned processes

doc/api/child_process.md

@@ -293,6 +293,8 @@ added: v0.1.90
 * `options` {Object}
   * `cwd` {String} Current working directory of the child process
   * `env` {Object} Environment key-value pairs
+  * `argv0` {String} Explicitly set the value of `argv[0]` sent to the child
+    process. This will be set to `command` if not specified.
   * `stdio` {Array|String} Child's stdio configuration. (See
     [`options.stdio`][`stdio`])
   * `detached` {Boolean} Prepare child to run independently of its parent
@@ -395,6 +397,14 @@ child.on('error', (err) => {
 });
 ```
 
+*Note: Certain platforms (OS X, Linux) will use the value of `argv[0]` for the
+process title while others (Windows, SunOS) will use `command`.*
+
+*Note: Node.js currently overwrites `argv[0]` with `process.execPath` on
+startup, so `process.argv[0]` in a Node.js child process will not match the
+`argv0` parameter passed to `spawn` from the parent, retrieve it with the
+`process.argv0` property instead.*
+
 #### options.detached
 <!-- YAML
 added: v0.7.10

doc/api/process.md

@@ -452,9 +452,10 @@ added: v0.1.27
 
 The `process.argv` property returns an array containing the command line
 arguments passed when the Node.js process was launched. The first element will
-be [`process.execPath`]. The second element will be the path to the
-JavaScript file being executed. The remaining elements will be any additional
-command line arguments.
+be [`process.execPath`]. See `process.argv0` if access to the original value of
+`argv[0]` is needed.  The second element will be the path to the JavaScript
+file being executed. The remaining elements will be any additional command line
+arguments.
 
 For example, assuming the following script for `process-args.js`:
 
@@ -481,6 +482,22 @@ Would generate the output:
 4: four
 ```
 
+## process.argv0
+<!-- YAML
+added: REPLACEME
+-->
+
+The `process.argv0` property stores a read-only copy of the original value of
+`argv[0]` passed when Node.js starts.
+
+```js
+$ bash -c 'exec -a customArgv0 ./node'
+> process.argv[0]
+'/Volumes/code/external/node/out/Release/node'
+> process.argv0
+'customArgv0'
+```
+
 ## process.chdir(directory)
 <!-- YAML
 added: v0.1.17

lib/child_process.js

@@ -347,7 +347,11 @@ function normalizeSpawnArguments(file /*, args, options*/) {
     }
   }
 
-  args.unshift(file);
+  if (typeof options.argv0 === 'string') {
+    args.unshift(options.argv0);
+  } else {
+    args.unshift(file);
+  }
 
   var env = options.env || process.env;
   var envPairs = [];

lib/internal/bootstrap_node.js

@@ -50,6 +50,11 @@
 
     _process.setupRawDebug();
 
+    Object.defineProperty(process, 'argv0', {
+      enumerable: true,
+      configurable: false,
+      value: process.argv[0]
+    });
     process.argv[0] = process.execPath;
 
     // There are various modes that Node can run in. The most common two

test/parallel/test-child-process-spawn-argv0.js

@@ -0,0 +1,18 @@
+'use strict';
+require('../common');
+const assert = require('assert');
+const cp = require('child_process');
+
+// This test spawns itself with an argument to indicate when it is a child to
+// easily and portably print the value of argv[0]
+if (process.argv[2] === 'child') {
+  console.log(process.argv0);
+  return;
+}
+
+const noArgv0 = cp.spawnSync(process.execPath, [__filename, 'child']);
+assert.strictEqual(noArgv0.stdout.toString().trim(), process.execPath);
+
+const withArgv0 = cp.spawnSync(process.execPath, [__filename, 'child'],
+    {argv0: 'withArgv0'});
+assert.strictEqual(withArgv0.stdout.toString().trim(), 'withArgv0');