Add File Commands (#571)

* Add File Commands

* pr updates w/ feedback

* run format

* fix lint/format

* slight update with an example in the docs

* pr feedback

packages/core/src/command.ts

@@ -1,4 +1,5 @@
 import * as os from 'os'
+import {toCommandValue} from './utils'
 
 // For internal use, subject to change.
 
@@ -76,19 +77,6 @@ class Command {
   }
 }
 
-/**
- * Sanitizes an input into a string so it can be passed into issueCommand safely
- * @param input input to sanitize into a string
- */
-export function toCommandValue(input: any): string {
-  if (input === null || input === undefined) {
-    return ''
-  } else if (typeof input === 'string' || input instanceof String) {
-    return input as string
-  }
-  return JSON.stringify(input)
-}
-
 function escapeData(s: any): string {
   return toCommandValue(s)
     .replace(/%/g, '%25')