Windows PowerShell Cmdlets
Introduction to Windows PowerShell CmdletsWith PowerShell you have a
choice, you can either type commands directly at the shell's command line,
or else you can store the same commands in a text file. Naturally, you
then call that script file, known as a cmdlet, from the PowerShell command
line, or in v 2.0, the ISE (Integrated Scripting Environment). As with other script languages,
notepad is an alternative vehicle for writing or editing scripts, the only
specific requirement is that you must save the cmdlet with the PowerShell extension
of .ps1. Writing scripts has two extra benefits, it documents your commands,
so that you don't forget them, and also, these cmdlet files provide a record of your PowerShell achievements.
PowerShell Cmdlet Topics
♣
First Meaning of
PowerShell Cmdlet
Microsoft say that a
cmdlet means a built-In PowerShell command, which corresponds to a single verb-Noun pair. Such a cmdlet is often accompanied by an alias, for example: Get-Member with its alias of gm.
Second Meaning of
PowerShell Cmdlet
In PowerShell circles there appears to be a second
meaning for the word cmdlet. A PowerShell cmdlet is a series of
commands, usually more than one line, stored in a text file with a .ps1
extension. It is this scriplet meaning of cmdlet that I feature on this page. Advantages of
Creating Cmdlets
Once you have experimented with a few basic instructions at the PowerShell
command line, you may wish to store your code in its own cmdlet file.
The benefit is that you can replay these perfect lines of instructions
later. The advent the ISE (Integrated Scripting Environment) in
PowerShell 2.0 makes this strategy easy to embrace.
My tactic is once my lines of code achieve my basic objective, I
call for 'SaveAs', and then use the copy for further development. Seven times out of ten the 'development' goes hopelessly wrong, at which point I am so grateful that I saved a working copy. I hope that you are getting the idea of a cmdlet. Spend time perfecting the PowerShell commands, then save them in a text file.
This technique saves you typing in lines of code and the command line, instead, you call
the cmdlet by typing: dot slash and followed by its filename, for example .\memory.
Incidentally, building PowerShell cmdlets fits in with my strategy of assembling
scripts in sections.
Guy
Recommends: Free WMI Monitor for PowerShell
Windows Management Instrumentation (WMI) is one of the hidden
treasures of Microsoft's operating systems. Fortunately, SolarWinds
have created a
Free WMI Monitor so that you can discover these gems of performance
information, and thus improve your PowerShell scripts.
Take the guess work out of which WMI counters to use when scripting the
operating system, Active Directory, or Exchange Server. Give this WMI monitor a
try - it's free.
Download your free copy of WMI Monitor
Creating PowerShell Cmdlets
- Quick InstructionsCreating these Windows PowerShell cmdlets is
straightforward, and most rewarding. Here are three essential tasks to ensure that the instructions in these script files execute correctly. -
For security, the operating system won't run PowerShell scripts by default. Thus we need to adjust the
ExecutionPolicy to allow PowerShell scripts to run. The better method is to issue this instruction at the PowerShell command line:
Set-ExecutionPolicy RemoteSigned. Alternatively you could
edit the registry.
- Make sure that you save the filename with a .ps1 extension.
However PowerShell ISE will do this automatically.
- In PowerShell 1.0 I learned the knack of calling the file from the PowerShell command line, either by typing the full path:
D: \scripts\filename, or if you were already in the D: \scripts folder, just type:
.\filename (note
the rhythm: dot slash filename).
- In PowerShell v 2.0 I simply open the files in the ISE and run them
in this GUI.
Note 1: Let me explain, this is how I like to call cmdlets from a subdirectory. D: \scripts is my main script directory, however, I create cmdlets in subdirectories such as: D: scripts\wmi\32proc.ps1 . Assuming that I am at the PowerShell command line in the D: \scripts folder, all that I type at the prompt is: .\wmi\32proc. .
Note 2: It took me ages to deduce that all I needed was plain .\filename. Avoid over-think, when you call the cmdlet file you
don't need to add the extension. Adding .ps1 is not necessary .\filename will suffice.
Note 3: While this dot slash (.\) method of executing the cmdlet script seems cumbersome, Microsoft decided on this method for security reasons. Hackers, phishers and the like could trick
people into executing a rogue PowerShell script by clicking on it. However, nothing happens - unless you proceed the script with .\ this safety feature offers a measure of protection from such mischief
makers.
The following instructions are the same as those above, but with extra step-by-step directions. 1a) PowerShell's
ExecutionPolicy command
I prefer this method, which employs PowerShell's own commands to control the
script Execution Policy. At the PS prompt try the following 3
commands:
# PowerShell Set-ExecutionPolicy
Get-ExecutionPolicy
# Now try:
Set-ExecutionPolicy -?
# Here is the crucial command:
Set-ExecutionPolicy RemoteSigned
See more on Set-ExecutionPolicy
Guy Recommends: A Free Trial of the Network Performance Monitor
(NPM)
SolarWinds'
Network Performance Monitor
will help you discover what's happening on your network. This
utility will also guide you through troubleshooting; the dashboard will
indicate whether the root cause is a broken link, faulty equipment or
resource overload.
What I like best is the way NPM suggests solutions to network
problems. Its also has the ability to monitor the health of individual VMware
virtual machines. If you are interested in troubleshooting, and creating
network maps, then I recommend that you try NPM now.
Download a free trial of Solarwinds' Network Performance Monitor
1b) PowerShell Registry AdjustmentFor security, and by default, Microsoft prevent PowerShell from executing cmdlet scripts;
consequently we need to change a specific registry setting to allow our cmdlets to execute. If you
don't make my amendment you may get the following error message when you call for a cmdlet script. 'The execution of scripts is disabled on this system'.
Our task is to open the registry and amend the value of the REG_SZ
ExecutionPolicy, specifically change Restricted to RemoteSigned. There
are two additional values called Unrestricted and AllSigned. However, RemoteSigned is the best because it allows you to run scripts locally,
while preventing people from hacking you from
other machines e.g. the internet. To check the setting launch regedit and navigate to: HKLM\SOFTWARE\Microsoft\PowerShell\1\ShellIds\Microsoft.PowerShell (In some versions of
PowerShell / Monad the path
maybe slightly different.
HKLM\SOFTWARE\Microsoft\PowerShell\1\ShellIds\Microsoft.Management.Automation.ps1) Change this registry key:
REG_SZ
ExecutionPolicy
RemoteSigned.
Filename and .ps1 extensionWhen you create your PowerShell cmdlet with notepad, the filename must have a .ps1 extension for example, RunningProcess.ps1. One way of creating such a file is to save your PowerShell
commands in notepad, then from the file menu: Save As, Type, All Files, RunningProcess.ps1. Just to
be doubly sure, you could put the filename in double quotes, for example: "RunningProcess.ps1". I maybe paranoid, but please check the file is not called RunningProcess.txt or RunningProcess.ps1.txt.
What you put in filename.ps1
are the same commands that you type in the PowerShell box. You could start
by creating a file with a simple verb-Noun
pair, for example just:
Get-Process.
This may seem too simple, but my philosophy is keep things straightforward and build on success. Here is a more advanced set of instructions just to give you the idea of the
joy of creating a PowerShell script.
# This script generates a report about Running Services
# Guy Thomas May
2010
"" # Insert a blank line
"Report generated at " + (Get-date)
""
# Insert blank line
"Services that are running"
Get-Service | where-object { $_.status -eq "Running"}
Learning Points
| 
