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Windows PowerShell Pocket Reference by Lee Holmes

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Chapter 4. PowerShell Automatic Variables

PowerShell defines and populates several variables automatically. These variables let you access information about the execution environment, PowerShell preferences, and more.

Table 4-1 provides a listing of these automatic variables and their meanings.

Table 4-1. Windows PowerShell automatic variables: Variables automatically used and set by Windows PowerShell

Variable

Meaning

$$

Last token of the last line received by the shell.

$?

Success/fail status of the last operation.

$^

First token of the last line received by the shell.

$_

Current pipeline object in a pipelined script block.

$args

Array of parameters passed to the script, function, or script block.

$confirmPreference

Preference that controls the level of impact that operations may have before requesting confirmation. Supports the values none, low, medium, high. A value of none disables confirmation messages.

$consoleFilename

Filename of the PowerShell console file that configured this session, if one was used.

$currentlyExecutingCommand

Currently executing command, when in a suspended prompt.

$debugPreference

Preference that controls how PowerShell should handle debug output written by a script or cmdlet. Supports the values SilentlyContinue, Continue, Inquire, and Stop.

$error

Array that holds the terminating and nonterminating errors generated in the shell.

$errorActionPreference

Preference that controls how PowerShell should handle error output written by a script or cmdlet. Supports the values SilentlyContinue, Continue, Inquire, and Stop.

$errorView

Preference that controls how PowerShell should output errors in the shell. Supports the values of Normal and CategoryView (a more succinct and categorical view of the error).

$executionContext

Means by which scripts can access the APIs typically used by cmdlets and providers.

$false

Variable that represents the Boolean value False.

$foreach

Enumerator within a foreach loop.

$formatEnumerationLimit

Limit on how deep into an object the formatting and output facilities travel before outputting an object.

$home

User’s home directory.

$host

Means by which scripts can access the APIs and implementation details of the current host and user interface.

$input

Current input pipeline in a pipelined script block.

$lastExitCode

Exit code of the last command. Can be explicitly set by scripts, and is automatically set when calling native executables.

$logEngineHealthEvent

Preference that tells PowerShell to log engine health events, such as errors and exceptions. Supports the values $true and $false.

$logEngineLifecycleEvent

Preference that tells PowerShell to log engine lifecycle events, such as Start and Stop. Supports the values $true and $false.

$logCommandHealthEvent

Preference that tells PowerShell to log command health events, such as errors and exceptions. Supports the values $true and $false.

$logCommandLifecycleEvent

Preference that tells PowerShell to log command lifecycle events, such as Start and Stop. Supports the values $true and $false.

$logProviderHealthEvent

Preference that tells PowerShell to log provider health events, such as errors and exceptions. Supports the values $true and $false.

$logProviderLifecycleEvent

Preference that tells PowerShell to log provider lifecycle events, such as Start and Stop. Supports the values $true and $false.

$matches

Results of the last successful regular expression match (through the –match operator).

$maximumAliasCount

Limit on how many aliases may be defined.

$maximumDriveCount

Limit on how many drives may be defined. Does not include default system drives.

$maximumErrorCount

Limit on how many errors PowerShell retains in the $error collection.

$maximumFunctionCount

Limit on how many functions may be defined.

$maximumHistoryCount

Limit on how many history items are retained.

$maximumVariableCount

Limit on how many variables may be defined.

$myInvocation

Information about the context under which the script, function, or script block was run, including detailed information about the command (MyCommand) and the script that defines it (ScriptName).

$nestedPromptLevel

Nesting level of the current prompt. Incremented by operations that enter a nested prompt (such as $host.EnterNestedPrompt( )) and decremented by the exit statement.

$null

Variable that represents the concept of Null.

$ofs

Output field separator. Placed between elements when PowerShell outputs a list as a string.

$outputEncoding

Character encoding used when sending pipeline data to external processes.

$pid

Process ID of the current PowerShell instance.

$profile

Location and filename of the PowerShell profile for this host.

$progressPreference

Preference that controls how PowerShell should handle progress output written by a script or cmdlet. Supports the values SilentlyContinue, Continue, Inquire, and Stop.

$psHome

Installation location of PowerShell.

$pwd

Current working directory.

$shellId

Shell identifier of this host.

$stackTrace

Detailed stack trace information of the last error.

$this

Reference to the current object in ScriptMethods and ScriptProperties.

$transcript

Filename used by the Start-Transcript cmdlet.

$true

Variable that represents the Boolean value True.

$verboseHelpErrors

Preference that tells PowerShell to output detailed error information when parsing malformed help files. Supports the values $true and $false.

$verbosePreference

Preference that controls how PowerShell should handle verbose output written by a script or cmdlet. Supports the values SilentlyContinue, Continue, Inquire, and Stop.

$warningPreference

Preference that controls how PowerShell should handle warning output written by a script or cmdlet. Supports the values SilentlyContinue, Continue, Inquire, and Stop.

$whatifPreference

Preference that controls how PowerShell should handle confirmation requests called by a script or cmdlet. Supports the values SilentlyContinue, Continue, Inquire, and Stop.

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