Automatic Variables All Versions

Examples

• 4

  $?

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  4

  Contains status of the last operation. When there is no error, it is set to True:

  PS C:\> Write-Host "Hello"
  Hello
  PS C:\> $?
  True
  

  If there is some error, it is set to False:

  PS C:\> wrt-host
  wrt-host : The term 'wrt-host' 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
  + wrt-host
  + ~~~~~~~~
      + CategoryInfo          : ObjectNotFound: (wrt-host:String) [], CommandNotFoundException
      + FullyQualifiedErrorId : CommandNotFoundException
  
  PS C:\> $?
  False
  

  edited Oct 25 at 19:11

  

  
• 4

  $OFS

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  4

  Variable called Output Field Separator contains string value that is used when converting an array to a string. By default $OFS = " " (a space), but it can be changed:

  PS C:\> $array = 1,2,3
  PS C:\> "$array" # default OFS will be used
  1 2 3
  PS C:\> $OFS = ",." # we change OFS to comma and dot
  PS C:\> "$array"
  1,.2,.    3
  

  created Aug 9 at 18:08

  
• 3

  $null

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  3

  $null is used to represent absent or undefined value.
  $null can be used as an empty placeholder for empty value in arrays:

  PS C:\> $array = 1, "string", $null
  PS C:\> $array.Count
  3
  

  When we use the same array as the source for ForEach-Object, it will process all three items (including $null):

  PS C:\> $array | ForEach-Object {"Hello"}
  Hello
  Hello
  Hello
  

  Be careful! This means that ForEach-Object WILL process even $null all by itself:

  PS C:\> $null | ForEach-Object {"Hello"} # THIS WILL DO ONE ITERATION !!!
  Hello
  

  Which is very unexpected result if you compare it to classic foreach loop:

  PS C:\> foreach($i in $null) {"Hello"} # THIS WILL DO NO ITERATION
  PS C:\>
  

  created Aug 9 at 18:08

  
• 1

  $_ / $PSItem

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  1

  Contains the object/item currently being processed by the pipeline.

  PS C:\> 1..5 | % { Write-Host "The current item is $_" }
  The current item is 1
  The current item is 2
  The current item is 3
  The current item is 4
  The current item is 5
  

  $PSItem and $_ are identical and can be used interchangeably, but $_ is by far the most commonly used.

  edited Dec 14 at 23:44

  

  
• 1

  $error

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  1

  Array of most recent error objects. The first one in the array is the most recent one:

  PS C:\> throw "Error" # resulting output will be in red font
  Error
  At line:1 char:1
  + throw "Error"
  + ~~~~~~~~~~~~~
      + CategoryInfo          : OperationStopped: (Error:String) [], RuntimeException
      + FullyQualifiedErrorId : Error
  
  PS C:\> $error[0] # resulting output will be normal string (not red    )
  Error
  At line:1 char:1
  + throw "Error"
  + ~~~~~~~~~~~~~
      + CategoryInfo          : OperationStopped: (Error:String) [], RuntimeException
      + FullyQualifiedErrorId : Error
  

  created Aug 9 at 18:08

  
• 1

  $pid

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  1

  Contains process ID of the current hosting process.

  PS C:\> $pid
  26080
  

  created Aug 9 at 18:08

  
• 1

  Boolean values

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  1

  $true and $false are two variables that represent logical TRUE and FALSE.

  Note that you have to specify the dollar sign as the first character (which is different from C#).

  created Aug 9 at 18:08