PowerShell provides another set of Automatic variables to allow us to get the information about the home directory, present working directory, host details, and error details. In this article, we will discuss these variables.
The $HOST Automatic Variable
This variable contains the current host application object for PowerShell. Below displays the details of the host application; like UI, host application Version, etc. We can also change the properties of the host application, using this variable.
PS C:\> $HOST Name : ConsoleHost Version : 4.0 InstanceId : 2a8d8964-2096-4e25-a68f-0a246a0d451e UI : System.Management.Automation.Internal.Host.InternalHostUserInterface CurrentCulture : en-US CurrentUICulture : en-US PrivateData : Microsoft.PowerShell.ConsoleHost+ConsoleColorProxy IsRunspacePushed : False Runspace : System.Management.Automation.Runspaces.LocalRunspace
Here it displays the properties of the host application. Let’s deeply look into UI property to use some of its properties. To display its properties it; we can use Get-Member cmdlet, like below.
PS C:\> $HOST.UI | Get-Member
TypeName: System.Management.Automation.Internal.Host.InternalHostUserInterface
Name MemberType Definition
---- ---------- ----------
Equals Method bool Equals(System.Object obj)
GetHashCode Method int GetHashCode()
GetType Method type GetType()
Prompt Method System.Collections.Generic.Dictionary[string,psobject] Prompt(string caption, string message, System.Collections.ObjectModel.Collection[System.Management.Automati...
PromptForChoice Method int PromptForChoice(string caption, string message, System.Collections.ObjectModel.Collection[System.Management.Automation.Host.ChoiceDescription] choices, int de...
PromptForCredential Method pscredential PromptForCredential(string caption, string message, string userName, string targetName), pscredential PromptForCredential(string caption, string mess...
ReadLine Method string ReadLine()
ReadLineAsSecureString Method securestring ReadLineAsSecureString()
ToString Method string ToString()
Write Method void Write(string value), void Write(System.ConsoleColor foregroundColor, System.ConsoleColor backgroundColor, string value)
WriteDebugLine Method void WriteDebugLine(string message)
WriteErrorLine Method void WriteErrorLine(string value)
WriteLine Method void WriteLine(), void WriteLine(string value), void WriteLine(System.ConsoleColor foregroundColor, System.ConsoleColor backgroundColor, string value)
WriteProgress Method void WriteProgress(long sourceId, System.Management.Automation.ProgressRecord record)
WriteVerboseLine Method void WriteVerboseLine(string message)
WriteWarningLine Method void WriteWarningLine(string message)
RawUI Property System.Management.Automation.Host.PSHostRawUserInterface RawUI {get;}We can use these properties of UI, directly. Let’s use WriteLine method to display some text on the screen.
PS C:\> $HOST.UI.WriteLine("Hello, World!")
Hello, World!Let’s look at another property; RawUI. This has the property to change the display color.
PS C:\PowerShell> $HOST.UI.RawUI ForegroundColor : Gray BackgroundColor : Black CursorPosition : 0,52 WindowPosition : 0,0 CursorSize : 25 BufferSize : 200,80 WindowSize : 197,66 MaxWindowSize : 200,69 MaxPhysicalWindowSize : 200,69 KeyAvailable : False WindowTitle : Administrator: Windows PowerShell
What we do now? Change the Background color and Window title and observe the UI appearance.
PS C:\> $HOST.UI.RawUI.BackgroundColor = "Blue" PS C:\> $HOST.UI.RawUI.WindowTitle = "CodeSteps - Host Variable demonstration" PS C:\> $HOST.UI.RawUI ForegroundColor : Gray BackgroundColor : Blue CursorPosition : 0,3 WindowPosition : 0,0 CursorSize : 25 BufferSize : 200,80 WindowSize : 82,31 MaxWindowSize : 200,69 MaxPhysicalWindowSize : 200,69 KeyAvailable : False WindowTitle : CodeSteps - Host Variable demonstration
Here is the screenshot with the applied changes:
The $HOME Automatic Variable
This variable contains the complete path of the User’s home directory.
PS C:\> $HOME C:\Users\david
The $PWD Automatic Variable
This variable contains the current working directory information.
PS C:\PowerShell> $PWD Path ---- C:\PowerShell
The $ERROR Automatic Variable
This variable contains error details. Each generated error will be stored in this variable; that means, it holds an array of error objects. The most recent error will be displayed first.
PS C:\PowerShell> ll ll : The term 'll' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify that the path is correct and try again. At line:1 char:1 + ll + ~~ + CategoryInfo : ObjectNotFound: (ll:String) [], CommandNotFoundException + FullyQualifiedErrorId : CommandNotFoundException PS C:\PowerShell> Get-Number Get-Number : The term 'Get-Number' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify that the path is correct and try again. At line:1 char:1 + Get-Number + ~~~~~~~~~~ + CategoryInfo : ObjectNotFound: (Get-Number:String) [], CommandNotFoundException + FullyQualifiedErrorId : CommandNotFoundException PS C:\PowerShell> $ERROR Get-Number : The term 'Get-Number' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify that the path is correct and try again. At line:1 char:1 + Get-Number + ~~~~~~~~~~ + CategoryInfo : ObjectNotFound: (Get-Number:String) [], CommandNotFoundException + FullyQualifiedErrorId : CommandNotFoundException ll : The term 'll' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify that the path is correct and try again. At line:1 char:1 + ll + ~~ + CategoryInfo : ObjectNotFound: (ll:String) [], CommandNotFoundException + FullyQualifiedErrorId : CommandNotFoundException PS C:\PowerShell>
We can also access specific error object details using its entry index. For example, to display the most recent error, we can use this variable using index value as $ERROR[0].
Note that, these variables are specific to the session. Once you closed the PowerShell session; the values will be reset to its default values.
We will discuss more topics as we go.
[..] David