Add return promise to the Module.runMain() branch.

index.js

@@ -253,7 +253,7 @@ function installPackages (specs, prefix, opts) {
 module.exports._execCommand = execCommand
 function execCommand (_existing, argv) {
   return findNodeScript(_existing, argv).then(existing => {
-    if (existing && !argv.nodeArg && !argv.shell && existing !== process.argv[1]) {
+    if (existing && !argv.alwaysSpawn && !argv.nodeArg && !argv.shell && existing !== process.argv[1]) {
       const Module = require('module')
       // let it take over the process. This means we can skip node startup!
       if (!argv.noYargs) {

locales/en.json

@@ -25,5 +25,6 @@
   "package": "package",
   "npx: installed %s in %ss": "npx: installed %s in %ss",
   "Suppress output from npx itself. Subcommands will not be affected.": "Suppress output from npx itself. Subcommands will not be affected.",
-  "Extra node argument when calling a node binary.": "Extra node argument when calling a node binary."
+  "Extra node argument when calling a node binary.": "Extra node argument when calling a node binary.",
+  "Always spawn a child process to execute the command.": "Always spawn a child process to execute the command."
 }

parse-args.js

@@ -179,6 +179,10 @@ function yargsParser (argv, defaultNpm) {
       type: 'string',
       describe: Y()`Location of the npm cache.`
     })
+    .option('always-spawn', {
+      describe: Y()`Always spawn a child process to execute the command.`,
+      type: 'boolean'
+    })
     .option('no-install', {
       type: 'boolean',
       describe: Y()`Skip installation if a package is missing.`