TOPIC
about_Automatic_Variables
SHORT DESCRIPTION
Describes variables that store state information for Windows PowerShell.
These variables are created and maintained by Windows PowerShell.
LONG DESCRIPTION
Here is a list of the automatic variables in Windows PowerShell:
$$
Contains the last token in the last line received by the session.
$?
Contains the execution status of the last operation. It contains
TRUE if the last operation succeeded and FALSE if it failed.
$^
Contains the first token in the last line received by the session.
$_
Contains the current object in the pipeline object. You can use this
variable in commands that perform an action on every object or on
selected objects in a pipeline.
$Args
Contains an array of the undeclared parameters and/or parameter
values that are passed to a function, script, or script block.
When you create a function, you can declare the parameters by using the
param keyword or by adding a comma-separated list of parameters in
parentheses after the function name.
$ConsoleFileName
Contains the path of the console file (.psc1) that was most
recently used in the session. This variable is populated when
you start Windows PowerShell with the PSConsoleFile parameter or
when you use the Export-Console cmdlet to export snap-in names to a
console file.
When you use the Export-Console cmdlet without parameters, it
automatically updates the console file that was most recently
used in the session. You can use this automatic variable to determine
which file will be updated.
$Error
Contains an array of error objects that represent the most
recent errors. The most recent error is the first error object in the
array ($Error[0]).
$Event
Contains a PSEventArgs object that represents the event that is being
processed. This variable is populated only within the Action block of
an event registration command, such as Register-ObjectEvent. The value
of this variable is the same object that the Get-Event cmdlet returns.
Therefore, you can use the properties of the $Event variable, such as
$Event.TimeGenerated , in an Action script block.
$EventSubscriber
Contains a PSEventSubscriber object that represents the event subscriber
of the event that is being processed. This variable is populated only
within the Action block of an event registration command. The value of
this variable is the same object that the Get-EventSubscriber cmdlet
returns.
$ExecutionContext
Contains an EngineIntrinsics object that represents the
execution context of the Windows PowerShell host. You can
use this variable to find the execution objects that are
available to cmdlets.
$False
Contains FALSE. You can use this variable to represent
FALSE in commands and scripts instead of using the string "false".
The string can be interpreted as TRUE if it is converted to a non-empty
string or to a non-zero integer.
$ForEach
Contains the enumerator of a ForEach-Object loop. You can use the
properties and methods of enumerators on the value of the $ForEach
variable. This variable exists only while the For loop is running. It
is deleted when the loop is completed.
$Home
Contains the full path of the user's home directory. This variable is
the equivalent of the %homedrive%%homepath% environment variables,
typically C:\Users\<UserName>.
$Host
Contains an object that represents the current host application
for Windows PowerShell. You can use this variable to represent the
current host in commands or to display or change the properties of
the host, such as $Host.version or $Host.CurrentCulture, or
$host.ui.rawui.setbackgroundcolor("Red").
$Input
Contains an enumerator that enumerates all input that is passed to a
function. The $input variable is available only to functions and script
blocks (which are unnamed functions). In the Process block of a
function, the $input variable enumerates the object that is currently
in the pipeline. When the Process block completes, there are no objects
left in the pipeline, so the $input variable enumerates an empty
collection. If the function does not have a Process block, then in the
End block, the $input variable enumerates the collection of all input to
the function.
$LastExitCode
Contains the exit code of the last Windows-based program that was run.
$Matches
The $Matches variable works with the -match and -notmatch operators.
When you submit scalar input to the -match or -notmatch operator, and
either one detects a match, they return a Boolean value and populate
the $Matches automatic variable with a hash table of any string values
that were matched. For more information about the -match operator, see
about_comparison_operators.
$MyInvocation
Contains an object with information about the current command, such as
a script, function, or script block. You can use the information in the
object, such as the path and file name of the script
($myinvocation.mycommand.path) or the name of a function
($myinvocation.mycommand.name) to identify the current command. This is
particularly useful for finding the name of the script that is running.
$NestedPromptLevel
Contains the current prompt level. A value of 0 indicates the original
prompt level. The value is incremented when you enter a nested level and
decremented when you exit it.
For example, Windows PowerShell presents a nested command prompt when
you use the $Host.EnterNestedPrompt method. Windows PowerShell also
presents a nested command prompt when you reach a breakpoint in the
Windows PowerShell debugger.
When you enter a nested prompt, Windows PowerShell pauses the current
command, saves the execution context, and increments the value of
the $NestedPromptLevel variable. To create additional nested command
prompts (up to 128 levels) or to return to the original command prompt,
complete the command, or type "exit".
The $NestedPromptLevel variable helps you track the prompt level. You
can create an alternative Windows PowerShell command prompt that
includes this value so that it is always visible.
$NULL
$null is an automatic variable that contains a NULL or empty value. You
can use this variable to represent an absent or undefined value in commands
and scripts.
Windows PowerShell treats $null as an object with a value, that is, as an
explicit placeholder, so you can use $null to represent an empty value in a
series of values.
For example, when $null is included in a collection, it is counted as one of
the objects.
C:\PS> $a = ".dir", $null, ".pdf"
C:\PS> $a.count
3
If you pipe the $null variable to the ForEach-Object cmdlet, it generates a
value for $null, just as it does for the other objects.
PS C:\ps-test> ".dir", "$null, ".pdf" | Foreach {"Hello"}
Hello
Hello
Hello
As a result, you cannot use $null to mean "no parameter value." A parameter
value of $null overrides the default parameter value.
However, because Windows PowerShell treats the $null variable as a placeholder,
you can use it scripts like the following one, which would not work if $null
were ignored.
$calendar = @($null, $null, “Meeting”, $null, $null, “Team Lunch”, $null)
$days = Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"
$currentDay = 0
foreach($day in $calendar)
{
if($day –ne $null)
{
"Appointment on $($days[$currentDay]): $day"
}
$currentDay++
}
Appointment on Tuesday: Meeting
Appointment on Friday: Team lunch
$PID
Contains the process identifier (PID) of the process that is hosting
the current Windows PowerShell session.
$Profile
Contains the full path of the Windows PowerShell profile for the
current user and the current host application. You can use this variable
to represent the profile in commands. For example, you can use it in
a command to determine whether a profile has been created:
test-path $profile
Or, you can use it in a command to create a profile:
new-item -type file -path $pshome -force
You can also use it in a command to open the profile in Notepad:
notepad $profile
$PSBoundParameters
Contains a dictionary of the active parameters and their current
values. This variable has a value only in a scope where parameters
are declared, such as a script or function. You can use it to
display or change the current values of parameters or to pass
parameter values to another script or function.
For example:
function test {
param($a, $b)
# Display the parameters in dictionary format.
$psboundparameters
# Call the Test1 function with $a and $b.
test1 @psboundparameters
}
$PsCmdlet
Contains an object that represents the cmdlet or advanced function
that is being run.
You can use the properties and methods of the object in your cmdlet
or function code to respond to the conditions of use. For example,
the ParameterSetName property contains the name of the parameter set
that is being used, and the ShouldProcess method adds the WhatIf and
Confirm parameters to the cmdlet dynamically.
For more information about the $PSCmdlet automatic variable, see
about_Functions_Advanced.
$PsCulture
Contains the name of the culture currently in use in the operating
system. The culture determines the display format of items such
as numbers, currrency, and dates. This is the value of the
System.Globalization.CultureInfo.CurrentCulture.Name property of the
system. To get the System.Globalization.CultureInfo object for the
system, use the Get-Culture cmdlet.
$PSDebugContext
While debugging, this variable contains information about the
debugging environment. Otherwise, it contains a NULL value.
As a result, you can use it to indicate whether the debugger has
control. When populated, it contains a PsDebugContext object that has
Breakpoints and InvocationInfo properties. The InvocationInfo property
has several useful properties, including the Location property. The
Location property indicates the path of the script that is being
debugged.
$PsHome
Contains the full path of the installation directory for Windows
PowerShell, typically, %windir%\System32\WindowsPowerShell\v1.0. You
can use this variable in the paths of Windows PowerShell files. For
example, the following command searches the conceptual Help topics for
the word "variable":
select-string -pattern variable -path $pshome\*.txt
$PSScriptRoot
Contains the directory from which a script module (.psm1) is being executed.
This variable allows script modules to use the module path to access other
resources. This variable is valid only in a script module (.psm1).
$PSSenderInfo
Contains information about the user who started the PSSession,
including the user identity and the time zone of the originating
computer. This variable is available only in PSSessions.
The $PSSenderInfo variable includes a user-configurable property,
ApplicationArguments, which, by default, contains only the
$PSVersionTable from the originating session. To add data to the
ApplicationArguments property, use the ApplicationArguments parameter
of the New-PSSessionOption cmdlet.
$PsUICulture
Contains the name of the user interface (UI) culture that is currently
in use in the operating system. The UI culture determines which text
strings are used for user interface elements, such as menus and
messages. This is the value of the
System.Globalization.CultureInfo.CurrentUICulture.Name property of the
system. To get the System.Globalization.CultureInfo object for the
system, use the Get-UICulture cmdlet.
$PsVersionTable
Contains a read-only hash table that displays details about the
version of Windows PowerShell that is running in the current session.
The table includes the following items:
CLRVersion: The version of the common language runtime (CLR)
BuildVersion: The build number of the current version
PSVersion: The Windows PowerShell version number
WSManStackVersion: The version number of the WS-Management stack
PSCompatibleVersions: Versions of Windows PowerShell that are
compatible with the current version
SerializationVersion The version of the serialization method
PSRemotingProtocolVersion
The version of the Windows PowerShell remote
management protocol
$Pwd
Contains a path object that represents the full path of the current
directory.
$ReportErrorShowExceptionClass
$ReportErrorShowInnerException
$ReportErrorShowSource
$ReportErrorShowStackTrace
The "ReportErrorShow" variables are defined in Windows PowerShell, but
they are not implemented. Get-Variable gets them, but they do not contain
valid data.
$Sender
Contains the object that generated this event. This variable is
populated only within the Action block of an event registration command.
The value of this variable can also be found in the Sender property of
the PSEventArgs (System.Management.Automation.PSEventArgs) object that
Get-Event returns.
$ShellID
Contains the identifier of the current shell.
$SourceArgs
Contains objects that represent the event arguments of the event that
is being processed. This variable is populated only within the Action
block of an event registration command. The value of this variable
can also be found in the SourceArgs property of the PSEventArgs
(System.Management.Automation.PSEventArgs) object that Get-Event
returns.
$SourceEventArgs
Contains an object that represents the first event argument that derives
from EventArgs of the event that is being processed. This variable is
populated only within the Action block of an event registration command.
The value of this variable can also be found in the SourceArgs property
of the PSEventArgs (System.Management.Automation.PSEventArgs) object
that Get-Event returns.
$StackTrace
Contains a stack trace for the most recent error.
$This
In a script block that defines a script property or script method, the
$This variable refers to the object that is being extended.
$True
Contains TRUE. You can use this variable to represent
TRUE in commands and scripts.
SEE ALSO
about_Hash_Tables
about_Preference_Variables
about_Variables
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