Tuesday, September 26, 2017

Objects. One of many ways PowerShell differs from Unix shells

In learning Powershell, one of the hardest things to wrap my head around is how it is, and is not, like Unix shells. While it does allow you to interact with your system and perform actions, such as running commands, executing scripts, or doing the same to remote systems, there are some differences. Like... everything is an object, instead of everything is a blob of text. This has taken some getting used to, but in many ways it really simplifies a lot of activities that in a Unix shell would take a pretty complex pipeline.

People often conflate the Unix shell, such as Bash, or Zsh, and the terminal, such as xterm, Gnome Terminal, iTerm, etc. The terminal is the application or hardware through which a user can interact with the Unix system. Back in the last millenium, the terminal started off as a teletypewriter, from which modern Unix and Unix-like operating systems still retain the 'tty' name. Nowadays, it's also common to see purely software implementations referred to as pseudo-terminals (pty), because they serve the same function but have no physical manifestation, which are used by Terminal Emulators. The shell that runs in the terminal is how users truly interact with the system. Bash, Zsh, Csh, Ksh, and their many derivatives or specialized shells (such as may be used at a car dealer, or a POS system, etc), are the utility through which the terminal becomes useful.

The only difference between a bash shell on the system console, tty0, and a bash shell running in a terminal emulator on a remote system connected via ssh, is the capabilities of the terminal to display output, and control input. The bash shell itself will be the same, and generally speaking, everything in the Unix shell is text. We run a command, such as `ls`, and we get back a blob of text that we, as humans, can interpret as a list of files and directories. We can further process, or parse, that text using tools like awk, sed, grep, etc. These additional tools allow us to filter output, take an action on a string in the output, count the number of items, etc, etc.

In the PowerShell ecosystem, the analog of the Terminal is the Host. Microsoft includes the "Console Host", which is the terminal-like window that opens if you run "Microsoft Powershell", and the "Windows Powershell ISE Host", which opens when you run the "Windows PowerShell ISE" application. Both of these windows serve as hosts for the PowerShell shell itself, and they actually provide different behaviors, too as far as output, debugging, etc. In PowerShell, everything is an object. When you run the date alias in PowerShell, you are presented a string representation of the current date and time, but that's just the display. What you actually get back is a [System.Datetime] or (shortened) [datetime]
object, which has all sorts of methods, properties, and metadata associated with it.

Here's an example just using the date command in bash on Linux:

tim@bash:~$ date
Tue Sep 26 11:13:38 DST 2017
tim@bash:~$ $(date)
Tue: command not found
tim@bash:~$ echo $(date)
Tue Sep 26 11:13:48 DST 2017

As you can see, the output of the date command is a string. There is no metadata or properties associated with a datestamp or timestamp, because we just have a string. Here is PowerShell's date:

tim@PS > date
Tuesday, September 26, 2017 11:19:30 AM

tim@PS > (date) | Get-Member

   TypeName: System.DateTime

Name                 MemberType     Definition
----                 ----------     ----------
Add                  Method         datetime Add(timespan value)
AddDays              Method         datetime AddDays(double value)
AddHours             Method         datetime AddHours(double value)
AddMilliseconds      Method         datetime AddMilliseconds(double value)
AddMinutes           Method         datetime AddMinutes(double value)
AddMonths            Method         datetime AddMonths(int months)
AddSeconds           Method         datetime AddSeconds(double value)
AddTicks             Method         datetime AddTicks(long value)
AddYears             Method         datetime AddYears(int value)
CompareTo            Method         int CompareTo(System.Object value), int ...
Equals               Method         bool Equals(System.Object value), bool E...
GetDateTimeFormats   Method         string[] GetDateTimeFormats(), string[] ...
GetHashCode          Method         int GetHashCode()
GetObjectData        Method         void ISerializable.GetObjectData(System....
GetType              Method         type GetType()
GetTypeCode          Method         System.TypeCode GetTypeCode(), System.Ty...
IsDaylightSavingTime Method         bool IsDaylightSavingTime()
Subtract             Method         timespan Subtract(datetime value), datet...
ToBinary             Method         long ToBinary()
ToBoolean            Method         bool IConvertible.ToBoolean(System.IForm...
ToByte               Method         byte IConvertible.ToByte(System.IFormatP...
ToChar               Method         char IConvertible.ToChar(System.IFormatP...
ToDateTime           Method         datetime IConvertible.ToDateTime(System....
ToDecimal            Method         decimal IConvertible.ToDecimal(System.IF...
ToDouble             Method         double IConvertible.ToDouble(System.IFor...
ToFileTime           Method         long ToFileTime()
ToFileTimeUtc        Method         long ToFileTimeUtc()
ToInt16              Method         int16 IConvertible.ToInt16(System.IForma...
ToInt32              Method         int IConvertible.ToInt32(System.IFormatP...
ToInt64              Method         long IConvertible.ToInt64(System.IFormat...
ToLocalTime          Method         datetime ToLocalTime()
ToLongDateString     Method         string ToLongDateString()
ToLongTimeString     Method         string ToLongTimeString()
ToOADate             Method         double ToOADate()
ToSByte              Method         sbyte IConvertible.ToSByte(System.IForma...
ToShortDateString    Method         string ToShortDateString()
ToShortTimeString    Method         string ToShortTimeString()
ToSingle             Method         float IConvertible.ToSingle(System.IForm...
ToString             Method         string ToString(), string ToString(strin...
ToType               Method         System.Object IConvertible.ToType(type c...
ToUInt16             Method         uint16 IConvertible.ToUInt16(System.IFor...
ToUInt32             Method         uint32 IConvertible.ToUInt32(System.IFor...
ToUInt64             Method         uint64 IConvertible.ToUInt64(System.IFor...
ToUniversalTime      Method         datetime ToUniversalTime()
DisplayHint          NoteProperty   DisplayHintType DisplayHint=DateTime
Date                 Property       datetime Date {get;}
Day                  Property       int Day {get;}
DayOfWeek            Property       System.DayOfWeek DayOfWeek {get;}
DayOfYear            Property       int DayOfYear {get;}
Hour                 Property       int Hour {get;}
Kind                 Property       System.DateTimeKind Kind {get;}
Millisecond          Property       int Millisecond {get;}
Minute               Property       int Minute {get;}
Month                Property       int Month {get;}
Second               Property       int Second {get;}
Ticks                Property       long Ticks {get;}
TimeOfDay            Property       timespan TimeOfDay {get;}
Year                 Property       int Year {get;}
DateTime             ScriptProperty System.Object DateTime {get=if ((& { Set...

Just look at all those properties and methods that are automatically associated with a [datetime] object.

tim@PS > (date).ToShortDateString()

tim@PS > (date).ToLongDateString()
Tuesday, September 26, 2017

tim@PS > (date).ToUniversalTime()

Tuesday, September 26, 2017 3:21:53 PM

tim@PS > (date).IsDaylightSavingTime()

tim@PS > (date).AddYears(5)

Monday, September 26, 2022 11:22:29 AM

tim@PS > (date).AddMinutes(27)

Tuesday, September 26, 2017 11:49:54 AM

PowerShell feels a bit like a mix of Perl (syntax) and Python (everything is an object), presented as an interactive shell (with a bunch of familiar feeling Linux-ish aliases preconfigured).

Next Up... Output

Monday, July 24, 2017

PowerShell on Linux

I've been working with Windows and VMware for a while now, and have really enjoyed learning PowerShell and PowerCLI. I've always preffered CLI tools to GUI tools. Possibly just because I'm old enough that the computers I started with didn't have Windows (or even X-Windows).

The more I use PowerShell, the more I like PowerShell, so I've decided to start managing the Linux servers I have at home with it, just for funsies.

The first step is to install PowerShell. PowerShell for Linux/Mac/Etc is v6, and still in beta at the time of this writing. I use Ubuntu Linux at home, and fortunately for my lazy self, there is a Apt Repo for PowerShell for Ubuntu 16.

curl https://packages.microsoft.com/keys/microsoft.asc | sudo apt-key add -
curl https://packages.microsoft.com/config/ubuntu/16.04/prod.list | sudo tee /etc/apt/sources.list.d/microsoft.list
sudo apt-get update
sudo apt-get install -y powershell

These steps were blantantly ripped off from the actual Ubuntu 16.04 Installation Instructions. If you aren't comfortable adding the repository, there are also instructions for manually downloading the .deb package and installing it.

tkennedy@vp-win10tk01:~$ powershell
PowerShell v6.0.0-beta.4
Copyright (C) Microsoft Corporation. All rights reserved.

PS /home/tkennedy> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      6.0.0-beta
PSEdition                      Core
GitCommitId                    v6.0.0-beta.4
OS                             Linux 4.4.0-43-Microsoft #1-Microsoft Wed Dec 31 14:42:53 PST 2014
Platform                       Unix
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
PSRemotingProtocolVersion      2.3
WSManStackVersion              3.0

In UNIX and Linux, everything is a file. The shell (bash, zsh, etc) kind of turn all those files into strings, and make them available to STDOUT, which can be used on a pipeline to do things like command | sed | awk | wc or something. In PowerShell, everything is an object, which can be very powerful, but which can also be overwhelming as you're trying to get used to having to understand each object's model. They are rarely the same.

How many files are there in this directory?

PS /home/tkennedy> find . -type f | wc -l

PS /home/tkennedy> (Get-ChildItem -Force -Recurse -File).Count

The really interesting piece here, is that if I want to do something with those files, on the unix side I have to parse the list of files that `find` gives me back, and then process each file to, say, get it's `stat` results, or something. Then I have to further process all that data. Because everything is a string.

With PowerShell, I can assign the results of the Get-ChildItem command to a variable, $files, and it will create a System.Array containing all the objects for the files that were found.

PS /home/tkennedy> $files = Get-ChildItem -Force -Recurse -File

Now, because everything is an object, the $files object that I created is basically an array of all the file objects that Get-ChildItem was able to identify, and each of those file objects has all the properties that corresponds to that type of object.

If I wanted a list of files, their sizes, and their modes:
PS /home/tkennedy> $files | Select Name, Mode, Length

Name                           Mode   Length
----                           ----   ------
.bash_history                  ---h--    263
.bash_logout                   ---h--    220
.bashrc                        ---h--   3771
.profile                       ---h--    655
.sudo_as_admin_successful      ---h--      0
.viminfo                       ---h--   3601
appstacks.json                 ------  45413
appstacks.py                   ------    247
ModuleAnalysisCache            --r---  36043
StartupProfileData-Interactive --r---  17788
nuget.config                   --r---     93
PSRepositories.xml             --r---   3498
ConsoleHost_history.txt        ------   1128

To see what kinds of properties are available in a PowerShell object, you can use the Get-Member cmdlet on the pipeline. This will show you all the member properties of the System.IO.FileInfo objects.

PS /home/tkennedy> $files | Get-Member

   TypeName: System.IO.FileInfo

Name                      MemberType     Definition
----                      ----------     ----------
LinkType                  CodeProperty   System.String LinkType{get=GetLinkType;}
Mode                      CodeProperty   System.String Mode{get=Mode;}
Target                    CodeProperty   System.Collections.Generic.IEnumerable`1[[System.String, System.Pri...
AppendText                Method         System.IO.StreamWriter AppendText()
CopyTo                    Method         System.IO.FileInfo CopyTo(string destFileName), System.IO.FileInfo ...
Create                    Method         System.IO.FileStream Create()
CreateText                Method         System.IO.StreamWriter CreateText()
Decrypt                   Method         void Decrypt()
Delete                    Method         void Delete()
Encrypt                   Method         void Encrypt()
Equals                    Method         bool Equals(System.Object obj)
GetHashCode               Method         int GetHashCode()
GetLifetimeService        Method         System.Object GetLifetimeService()
GetObjectData             Method         void GetObjectData(System.Runtime.Serialization.SerializationInfo i...
GetType                   Method         type GetType()
InitializeLifetimeService Method         System.Object InitializeLifetimeService()
MoveTo                    Method         void MoveTo(string destFileName)
Open                      Method         System.IO.FileStream Open(System.IO.FileMode mode), System.IO.FileS...
OpenRead                  Method         System.IO.FileStream OpenRead()
OpenText                  Method         System.IO.StreamReader OpenText()
OpenWrite                 Method         System.IO.FileStream OpenWrite()
Refresh                   Method         void Refresh()
Replace                   Method         System.IO.FileInfo Replace(string destinationFileName, string desti...
ToString                  Method         string ToString()
PSChildName               NoteProperty   string PSChildName=.bash_history
PSDrive                   NoteProperty   PSDriveInfo PSDrive=/
PSIsContainer             NoteProperty   bool PSIsContainer=False
PSParentPath              NoteProperty   string PSParentPath=Microsoft.PowerShell.Core\FileSystem::/home/tke...
PSPath                    NoteProperty   string PSPath=Microsoft.PowerShell.Core\FileSystem::/home/tkennedy/...
PSProvider                NoteProperty   ProviderInfo PSProvider=Microsoft.PowerShell.Core\FileSystem
Attributes                Property       System.IO.FileAttributes Attributes {get;set;}
CreationTime              Property       datetime CreationTime {get;set;}
CreationTimeUtc           Property       datetime CreationTimeUtc {get;set;}
Directory                 Property       System.IO.DirectoryInfo Directory {get;}
DirectoryName             Property       string DirectoryName {get;}
Exists                    Property       bool Exists {get;}
Extension                 Property       string Extension {get;}
FullName                  Property       string FullName {get;}
IsReadOnly                Property       bool IsReadOnly {get;set;}
LastAccessTime            Property       datetime LastAccessTime {get;set;}
LastAccessTimeUtc         Property       datetime LastAccessTimeUtc {get;set;}
LastWriteTime             Property       datetime LastWriteTime {get;set;}
LastWriteTimeUtc          Property       datetime LastWriteTimeUtc {get;set;}
Length                    Property       long Length {get;}
Name                      Property       string Name {get;}
BaseName                  ScriptProperty System.Object BaseName {get=if ($this.Extension.Length -gt 0){$this...
VersionInfo               ScriptProperty System.Object VersionInfo {get=[System.Diagnostics.FileVersionInfo]...

And all of those properties are available to you, and to other cmdlets in PowerShell to parse, filter on, operate on, print out, etc, etc. The shell is your oyster!

Wednesday, March 29, 2017

PrivateInternetAccess VPN on a Ubiquiti USG (Unifi Security Gateway)

Big news this week, as the Republicans in Congress decided to scrap an FCC rule known as the Broadband Consumer Privacy Proposal which required broadband providers to get permission from subscribers before collecting and selling data collected about their users.

Since I am very interested in my online privacy, or at least, I like to have the option to choose when to share my information for myself, and since I recently upgraded my home router to a Unifi Security Gateway from Ubiquiti Networks, I wanted to know if the VPN client would be compatible with the Private Internet Access VPN that I use to protect my privacy, thereby putting my entire house behind the VPN all the time.

Posts in the UBNT Community Forums seem to have a lot of confusion, or are just outdated.

It turns out the setup for a PIA VPN configuration is very easy.

The only thing that posed any challenge was calculating all the routes for all the subnets outside my house, to route that traffic over the VPN. In my case, since I use RFC1918 space, here is the list of routes I needed to add to the USG, via the "subnets" menu item in the USG settings app:


Since hosts have a default route to the USG (, all traffic will make it to the USG just fine. Now... the USG has a default route to the internet via my ISP. The default route is, which is the least specific route possible to have in a routing table... a route to every IP possible. In routing, more specific routes always win. So the USG also has a local route to, which prevents my internal traffic from following the default route. And the USG has a more specific route to it's gateway than default as well, due to it being a connected network so it won't get lost in the routes above.

The list of subnets above provides a more specific route than the default route for every possible IP that is not in my house, which forces everything to be sent across the VPN, but they are still the least specific possible routes to everything, which means they're pretty easy to override if I don't want something going over the VPN. After all, the VPN is pretty limited on bandwidth compared to going directly out FiOS.

This list is everything that I don't use in my house, and ensures that any traffic to anywhere outside my house will be routed over the VPN. And, Yes, I am aware that there are other blocks of RFC1918 and RFC5737 space, but since ISPs don't route those networks, I'm not worried about them, because the VPN essentially acts as a sink for any traffic to those destinations.

Here is how the settings go into the USG configuration in the Unifi controller application:


  • Purpose: VPN Client
  • VPN Client: PPTP
  • Enabled: check this when you want the VPN to go live
  • Remote Subnets: one entry for each of the subnets in the list above (modified for your own use, if you don't use 192.168.x.x in your house/business)
  • Server IP: get this from PIA, I used `nslookup us-east.privateinternetaccess.com`
  • Username: your PIA username
  • Password: your PIA password
  • MPPE: Yes. You definitely want to have your VPN connection encrypted.

Enjoy your ISP not selling your internet activities to advertisers.

Sunday, March 19, 2017

Waking up gently with Sonos and Sirius XM and a Fade-In Alarm.

We (my wife and I) have been using LIFX lights in our bedroom to simulate a sunrise.  They come on at sunrise, and slowly increase brightness for 30 minutes, allowing us to get used to the light, and wake up pretty gently, as opposed to being jarred out of a deep sleep by a more traditional alarm clock.

My wife asked if there was any way we could do the same with Sonos.  Specifically, she wants to pick a Sirius XM channel like "15 - The Pulse" to wake up to.  Have the volume start at 0, and over the same 30 minute period as the lights, ramp the volume up slowly until it's a reasonable level coinciding with the maximum brightness of our lights.

Her ideal solution would have the following features:

  • Pick any Sirius, Pandora, or Calm Radio station that Sonos can regularly access.
  • Choose a maximum volume for the alarm
  • Choose a length of time over which to go from 0 to Max volume
  • Orchestrate the details via an iOS app on iPhone or iPad.

For Extra Credit:

  • Do the same thing in reverse, allowing from from X - 0 over time, like a slow ramp down sleep timer.

We first tried the Alarms available in the Sonos App.  These are time and content alarms, meaning I can set it to play a Sirius XM channel, at a specific time, at a specific volume.  There is a fade-in, but it's only 15 seconds long.  Not exactly what we're looking for.  We want something more along the lines of a 30 minute fade in.

Google seems to indicate that this is a common request from Sonos users:

I did end up finding https://github.com/SoCo/SoCo, a Python library for interacting and controlling Sonos speakers.

This library would allow me to hit about 2.5 of the ideal features, and possibly the extra credit as well, if I wrote a little program to run from cron on a Linux server.  

Easy to do in cron:

  • Run a program at a specific time 

Can do with SoCo:

  • Set volume of a Sonos speaker, or a group of speakers
  • Pick a channel to play

Can't easily do with Soco/Cron/Linux:

  • Control via an iOS app on iPhone/iPad.

Added Feature:

  • Supports a file in the same directory called 'holidays.txt', where I can put dates in the format YYYY-MM-DD (one per line), to not run the alarm. (like Work holidays)
  • I can also log in to the server and `touch /tmp/holiday` if I want the alarm to not go off tomorrow. (example: sick day, or unplanned day off)

So, I'm still on the look out for an iOS app that will let me orchestrate all this, at least until Sonos adds this kind of feature or one of the other home automation apps adds it. Here's a link to my alarm script: https://github.com/tksunw/IoT/tree/master/SONOS