GS 4: PowerShell’s Cmdlets

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　　With 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.
　　As with other script languages, notepad is an adequate vehicle for writing or editing scripts, the only PowerShell specific requirement is that you must save the cmdlet with a .ps1 file extension. (Note
　　this differs from the Monad Beta where the extension was .msh). Writing scripts has two extra benefits, it documents your commands, so that you don't forget them, and also, these cmdlet files
　　provide a proud record of your PowerShell achievements.
　　1. Cmdlets (Command Lets)
　　First Meaning of Cmdlet
　　Cmdlet has two meanings in Powershell; the first meaning of cmdlet is a synonym with a PowerShell script. A 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.
　　Second Meaning of Cmdlet
　　In PowerShell circles there appears to be a second meaning for the word cmdlet. For example , Microsoft say: 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.
　　Advantages of 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. This strategy becomes more and more useful as the code grow in complexity. My tactic is once a cmdlet achieves 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>　　instead, you call the cmdlet by typing: dot slash and followed by its filename, for example .\memory. Incidentally, building cmdlets fits in with my strategy of assembling scripts in sections.
　　2. Cmdlets - Three Quick Instructions
　　Creating these 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.>
  
• Make sure that you save the filename with a .ps1 extension
  
• Learn 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).
  

　　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.
　　Cmdlets Detailed Instructions
　　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 type:
　　get-executionpolicy
　　Now try: set-executionpolicy -?
　　Here is the crucial command:
　　set-executionpolicy RemoteSigned
　　N. B. get-executionpolicy is available in PowerShell but not in the Monad beta.
　　1b) PowerShell Registry Adjustment
　　For 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
　　Change this registry key:
　　REG_SZ ExecutionPolicy RemoteSigned.
　　2a) Filename and .ps1 extension
　　When you create your 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>　　# RunningServices.ps1
　　# This script generates a report about Running Services
　　# Guy Thomas September 2007
　　# Version 1. 5
　　"" # Insert a blank line
　　"Report generated at " + (get-date)
　　"" # Insert blank line
　　"Services that are running"
　　get-service | where-object { $_.status -eq "Running"}
　　Learning Points
　　Note 1: The key command in this example is: get-service. Observe the singular noun service, furthermore, PowerShell specializes in consistency, thus nouns are always singular.
　　Note 2: Let us dissect the where clause. {$_, is a special variable to indicate, in the current pipeline. The dollar sign indicates we are using a variable and the underscore has the special meaning, a value
　　in this stream. The process object has many properties, amongst them is .status. -eq means the left side equals the right side value. Observe the cmdlet and see that in this instance, we are looking for
　　a value held by $_.status equal to "Running" and not equal "Stopped".
　　Trap: { $_.status = "Running"} Remember that PowerShell introduces comparisons with a hyphen and not an equal sign, thus we have -eq -match, -contains.
　　2b) Calling the filename
　　Assumptions: You saved the cmdlet script files into a directory called D:\ scripts. Also, in my example, I assume that the actual file is called RunningServices.ps1 .
　　When you execute the cmdlet by calling the filename from the PowerShell command line, you don't need to add the .ps1 extension. However, you need to pay attention to the path. Start at the
　　command line by typing the full path, for example, D:\ scripts\RunningServices.
　　When that works, build on success. Navigate in PowerShell to the D:\ scripts folder, to achieve that,
　　you could try this command
　　set-location d:\ scripts
　　Now issue the shorter command: .\RunningServices (Rather than D:\ scripts\RunningServices)
　　Note: Observe the dot and the slash in front of the filename, incidentally the slash can be either a backslash or a forward-slash, therefore, ./runningservices works.
　　Copy and Paste Into PowerShell

　　If, for what ever reason, you do not wish to use a cmdlet, the>　　Summary of Cmdlets in PowerShell
　　When you execute PowerShell commands you have a choice, either just type the instructions at the Microsoft Shell command line, or create cmdlets scripts which you then call from the PS > prompt.
　　Remember before you start experimenting with PowerShell scripts, change the executionpolicy to RemoteSigned. To enable scripts to run locally, type this command:
　　set-executionpolicy RemoteSigned
　　As a result the PowerShell registry will now permit .ps1 files to execute at the PowerShell command line.