display an error in case OSX specific command is executed on other OS

re-natal.coffee

@@ -55,6 +55,12 @@ ensureExecutableAvailable = (executable) ->
   else
     exec "type #{executable}"
 
+ensureOSX = (cb) ->
+  if os.platform() == 'darwin'
+    cb()
+  else
+    logErr 'This command is only available on OSX'
+
 readFile = (path) ->
   fs.readFileSync path, encoding: 'ascii'
 
@@ -115,7 +121,7 @@ ensureFreePort = (cb) ->
 
 ensureXcode = (cb) ->
   try
-    exec 'type xcodebuild'
+    ensureExecutableAvailable 'xcodebuild'
     config = readConfig()
     unless config.device?
       config.device = getUuidForDevice 'iPhone 6'
@@ -570,6 +576,7 @@ cli.command 'init <name>'
 cli.command 'launch'
   .description 'compile project and run in iOS simulator'
   .action ->
+    ensureOSX ->
       ensureXcode ->
         ensureFreePort -> launch readConfig()
 
@@ -581,6 +588,7 @@ cli.command 'upgrade'
 cli.command 'listdevices'
   .description 'list available simulator devices by index'
   .action ->
+    ensureOSX ->
       ensureXcode ->
         console.log (getDeviceList()
           .map (line, i) -> "#{i}\t#{line.replace /\[.+\]/, ''}"
@@ -589,6 +597,7 @@ cli.command 'listdevices'
 cli.command 'setdevice <index>'
   .description 'choose simulator device by index'
   .action (index) ->
+    ensureOSX ->
       ensureXcode ->
         unless device = getDeviceList()[parseInt index, 10]
           logErr 'Invalid device index. Run re-natal listdevices for valid indexes.'
@@ -600,6 +609,7 @@ cli.command 'setdevice <index>'
 cli.command 'xcode'
   .description 'open Xcode project'
   .action ->
+    ensureOSX ->
       ensureXcode ->
         openXcode readConfig().name