Commit 6bd0631

@@ -33,7 +33,7 @@ function substitute(arg) {
   if (arg instanceof ProcessOutput) {
     return arg.stdout.replace(/\n$/, '')
   }
-  return arg
+  return arg.toString()
 }
 
 export function $(pieces, ...args) {

@@ -72,6 +72,12 @@ import {strict as assert} from 'assert'
   console.log(__filename, __dirname)
 }
 
+{
+  let foo = 0
+  let p = await $`echo -n ${foo}`
+  assert(p.stdout === '0')
+}
+
 {
   const {name, version} = require('./package.json')
   assert(typeof name === 'string')