Getting Summary Command Information in Windows PowerShell
The Windows PowerShell Get-Command cmdlet retrieves the names of all available commands. When you type Get-Command at a Windows PowerShell prompt, you will see output similar to the following:
| PS> Get-Command CommandType Name Definition ----------- ---- ---------- Cmdlet Add-Content Add-Content [-Path] <String[... Cmdlet Add-History Add-History [[-InputObject] ... Cmdlet Add-Member Add-Member [-MemberType] <PS... ... |
This output looks a lot like the Help output of Cmd.exe: a tabular summary of internal commands. In the extract of the Get-Command command output shown above, every command shown has a CommandType of Cmdlet. A Cmdlet is Windows PowerShell's intrinsic command type that corresponds roughly to the dir and cd commands of Cmd.exe and to built-ins in UNIX shells such as BASH.
In the output of the Get-Command command, all of the definitions end with ellipses (...) to indicate that PowerShell cannot display all of the content in the available space. When Windows PowerShell displays output, it formats the output as text and then arranges it to make the data fit cleanly into a console window. We will talk about this later in the section on formatters.
The Get-Command cmdlet has a Syntax parameter that allows you to retrieve just the syntax of each cmdlet. Enter the Get-Command -Syntax command to display the full output:
| PS> Get-Command -Syntax Add-Content [-Path] <String[]> [-Value] <Object[]> [-PassThru] [-Filter <String>] [-Include <String[]>] [-Exclude <String[]>] [-Force] [Credential <PSCredential>] [-Verbose] [-Debug] [-ErrorAction <ActionPreference>] [-ErrorVariable <String>] [-OutVariable <String>] [-OutBuffer <Int32>] [-WhatIf] [-Confirm] [-Encoding <FileSystemCmdletProviderEncoding>] Add-History [[-InputObject] <PSObject[]>] [-Passthru] [-Verbose] [-Debug] [-ErrorAction <ActionPreference>] [-ErrorVariable <String>] [-OutVariable <String>][-OutBuffer <Int32>]... |
Cmdlets Use Standard Parameters in Windows PowerShell
Cmdlets Use Standard Parameters
As noted earlier, commands used in traditional command-line interfaces do not generally have consistent parameter names. Sometimes parameters do not have names at all. When they do, they are often single-character or abbreviated words that can be typed rapidly but are not easily understood by new users.
Unlike most other traditional command-line interfaces, Windows PowerShell processes parameters directly, and uses this direct access to the parameters along with developer guidance to standardize parameter names. Although this does not guarantee that every cmdlet will always conform to the standards, it does encourage it.
Note:
Parameter names always have a '-' prepended to them when you use them, to allow Windows PowerShell to clearly identify them as parameters. In the Get-Command -Name Clear-Host example, the parameter's name is Name, but it is entered as -Name.
Here are some of the general characteristics of the standard parameter names and usages.
The Help Parameter (?)
When you specify the -? parameter to any cmdlet, the cmdlet is not executed. Instead, Windows PowerShell displays help for the cmdlet.
Common Parameters
Windows PowerShell has several parameters known as common parameters. Because these parameters are controlled by the Windows PowerShell engine, whenever they are implemented by a cmdlet, they will always behave the same way. The common parameters are WhatIf, Confirm, Verbose, Debug, Warn, ErrorAction, ErrorVariable, OutVariable, and OutBuffer.
Suggested Parameters
The Windows PowerShell core cmdlets use standard names for similar parameters. Although the use of parameter names is not enforced, there is explicit guidance for usage to encourage standardization.
For example, the guidance recommends naming a parameter that refers to a computer by name as ComputerName, rather than Server, Host, System, Node, or other common alternative words. Among the important suggested parameter names are Force, Exclude, Include, PassThru, Path, and CaseSensitive.
Posted in: Windows| Tags: Windows PowerShell PowerShell Windows cmdlets Parameters Help Parameter Common Parameters Suggested ParametersCmdlets Use Verb-Noun Names to Reduce Command Memorization in Windows PowerShell
Windows PowerShell uses a "verb-noun" naming system, where each cmdlet name consists of a standard verb hyphenated with a specific noun. Windows PowerShell verbs are not always English verbs, but they express specific actions in Windows PowerShell. Nouns are very much like nouns in any language, they describe specific types of objects that are important in system administration. It is easy to demonstrate how these two-part names reduce learning effort by looking at a few examples of verbs and nouns.
Nouns are less restricted, but they should always describe what a command acts upon. Windows PowerShell has commands such as Get-Process, Stop-Process, Get-Service, and Stop-Service.
In the case of two nouns and two verbs, consistency does not simplify learning that much. However, if you look at a standard set of 10 verbs and 10 nouns, you then have only 20 words to understand, but those words can be used to form 100 distinct command names.
Frequently, you can recognize what a command does by reading its name, and it is usually apparent what name should be used for a new command. For example, a computer shutdown command might be Stop-Computer. A command that lists all computers on a network might be Get-Computer. The command that gets the system date is Get-Date.
You can list all commands that include a particular verb with the -Verb parameter for Get-Command (We will discuss Get-Command in detail in the next section). For example, to see all cmdlets that use the verb Get, type:
| PS> Get-Command -Verb Get CommandType Name Definition ----------- ---- ---------- Cmdlet Get-Acl Get-Acl [[-Path] <String[]>]... Cmdlet Get-Alias Get-Alias [[-Name] <String[]... Cmdlet Get-AuthenticodeSignature Get-AuthenticodeSignature [-... Cmdlet Get-ChildItem Get-ChildItem [[-Path] <Stri... ... |
The -Noun parameter is even more useful because it allows you to see a family of commands that affect the same type of object. For example, if you want to see which commands are available for managing services, type following command:
| PS> Get-Command -Noun Service CommandType Name Definition ----------- ---- ---------- Cmdlet Get-Service Get-Service [[-Name] <String... Cmdlet New-Service New-Service [-Name] <String>... Cmdlet Restart-Service Restart-Service [-Name] <Str... Cmdlet Resume-Service Resume-Service [-Name] <Stri... Cmdlet Set-Service Set-Service [-Name] <String>... Cmdlet Start-Service Start-Service [-Name] <Strin... Cmdlet Stop-Service Stop-Service [-Name] <String... Cmdlet Suspend-Service Suspend-Service [-Name] <Str... ... |
A command is not necessarily a cmdlet, just because it has a verb-noun naming scheme. One example of a native Windows PowerShell command that is not a cmdlet but has a verb-noun name, is the command for clearing a console window, Clear-Host. The Clear-Host command is actually an internal function, as you can see if you run Get-Command against it:
| PS> Get-Command -Name Clear-Host CommandType Name Definition ----------- ---- ---------- Function Clear-Host $spaceType = [System.Managem... |
Understanding Important Windows PowerShell Concepts
The Windows PowerShell design integrates concepts from many different environments. Several of them are familiar to people with experience in specific shells or programming environments, but very few people will know about all of them. Looking at some of these concepts provides a useful overview of the shell.
Commands are not Text-based
Unlike traditional command-line interface commands, Windows PowerShell cmdlets are designed to deal with objects - structured information that is more than just a string of characters appearing on the screen. Command output always carries along extra information that you can use if you need it. We will discuss this topic in depth in this document.
If you have used text-processing tools to process command-line data in the past, you will find that they behave differently if you try to use them in Windows PowerShell. In most cases, you do not need text-processing tools to extract specific information. You can access portions of the data directly by using standard Windows PowerShell object manipulation commands.
The Command Family is Extensible
Interfaces such as Cmd.exe do not provide a way for you to directly extend the built-in command set. You can create external command-line tools that run in Cmd.exe, but these external tools do not have services, such as help integration, and Cmd.exe does not automatically know that they are valid commands.
The native binary commands in Windows PowerShell, known as cmdlets (pronounced command-lets), can be augmented by cmdlets that you create and that you add to Windows PowerShell by using snap-ins. Windows PowerShell snap-ins are compiled, just like binary tools in any other interface. You can use them to add Windows PowerShell providers to the shell, as well as new cmdlets.
Because of the special nature of the Windows PowerShell internal commands, we will refer to them as cmdlets.
Note:
Windows PowerShell can run commands other than cmdlets. We will not be discussing them in detail in the Windows PowerShell Primer, but they are useful to know about as categories of command types. Windows PowerShell supports scripts that are analogous to UNIX shell scripts and Cmd.exe batch files, but have a .ps1 file name extension. Windows PowerShell also allows you to create internal functions that can be used directly in the interface or in scripts.
Windows PowerShell Handles Console Input and Display
When you type a command, Windows PowerShell always processes the command-line input directly. Windows PowerShell also formats the output that you see on the screen. This is significant because it reduces the work required of each cmdlet and ensures that you can always do things the same way regardless of which cmdlet you are using. One example of how this simplifies life for both tool developers and users is command-line help.
Traditional command-line tools have their own schemes for requesting and displaying help. Some command-line tools use /? to trigger the help display; others use -?, /H, or even //. Some will display help in a GUI window, rather than in the console display. Some complex tools, such as application updaters, unpack internal files before displaying their help. If you use the wrong parameter, the tool might ignore what you typed and begin performing a task automatically.
When you enter a command in Windows PowerShell, everything you enter is automatically parsed and pre-processed by Windows PowerShell. If you use the -? parameter with a Windows PowerShell cmdlet, it always means "show me help for this command". Cmdlet developers do not have to parse the command; they only need to provide the help text.
It is important to understand that the help features of Windows PowerShell are available even when you run traditional command-line tools in Windows PowerShell. Windows PowerShell processes the parameters and passes the results to the external tools.
Note:
If you run an graphic application in Windows PowerShell, the window for the application opens. Windows PowerShell intervenes only when processing the command-line input you supply or the application output returned to the console window; it does not affect how the application works internally.
Windows PowerShell Uses Some C# Syntax
Windows PowerShell has syntax features and keywords that are very similar to those used in the C# programming language, because Windows PowerShell is based on the .NET framework. Learning Windows PowerShell will make it much easier to learn C#, if you are interested in the language.
If you are not a C# programmer, this similarity is not important. However, if you are already familiar with C#, the similarities can make learning Windows PowerShell much easier.
Posted in: Windows| Tags: Windows PowerShell PowerShell Windows Command Family binary commands internal commands cmdlets Text-based C# programmer C# .NET framework command-line