Category:Variables (PowerShell)

From vWiki
Jump to navigation Jump to search

All variable names are prefixed with a $, and are case insensitive (though there's no reason to not use CamelBack notation if that floats your boat).

Apart from a few reserved words and characters there's little restriction on what can be used, though note that this flexibility can cause the occasional issue, whereby PowerShell gets confused as to where a variable name finishes. Variable names can be enclosed in { } in order to delimit them, eg ${varname}.

PowerShell is all about manipulating objects, and all variables are objects. When you assign a value to a new variable, the type of object that it is (string, integer, etc) is automatically defined. Which is normally useful as you don't have to worry about what type of object/variable you want to create, PowerShell will work it out for you. However sometimes you need to force a variable to contain a specific data type to avoid errors or other problems down the line. Using a prefix of [type] achieves this...

 [string]$result = $PingResult.Status

Data types

Notation Data Type
[adsi] Active Directory Services object
[array] Array (see Arrays)
[bool] True / false (can also be [boolean])
[byte] 8-bit unsigned character
[char] Single character
[datetime] Date and time (see Datetime)
[decimal] 128-bit decimal
[double] Double-precision 64-bit floating point number
[int] 32-bit integer
[long] 64-bit integer
[single] Single-precision 32-bit floating point number
[string] String of characters (see Strings)
[timespan] Duration of time
[wmi] Windows Management Instrumentation (WMI) instance or collection
[wmiclass] WMI class
[xml] XML object

Variable Information

As PowerShell object (variables) tend to be black boxes that can contain anything or nothing, its often necessary to understand more about one. All objects contain Properties and Methods.

  • Properties
    • Are containers for data
  • Methods
    • Are in-built functions that allow an object to be manipulated.

Variable Type

To see the object type of a variable...

PS E:\> $var.GetType()
IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
True     True     Object[]                                 System.Array

Variable Properties

Simple objects such as strings will contain only one property but complicated can contain many more, and even further objects. If you pipe an object through Format-List you get a fuller picture...

PS E:\> Get-WMIObject Win32_BIOS

SMBIOSBIOSVersion : 786F3 v01.16
Manufacturer      : Hewlett-Packard
Name              : Default System BIOS
SerialNumber      : CPC123456J
Version           : HPQOEM - 20090219

PS E:\> Get-WMIObject Win32_BIOS | Format-List *

Status                : OK
Name                  : Default System BIOS
Caption               : Default System BIOS
SMBIOSPresent         : True
SMBIOSBIOSVersion     : 786F3 v01.16
SMBIOSMajorVersion    : 2
SMBIOSMinorVersion    : 6
SoftwareElementID     : Default System BIOS
SoftwareElementState  : 3
TargetOperatingSystem : 0
Version               : HPQOEM - 20090219
Scope                 : System.Management.ManagementScope
Path                  : \\LAPTOP1\root\cimv2:Win32_BIOS.Name="Default System BIOS",SoftwareElementID="Default System BI
                        OS",SoftwareElementState=3,TargetOperatingSystem=0,Version="HPQOEM - 20090219"
Options               : System.Management.ObjectGetOptions
ClassPath             : \\LAPTOP1\root\cimv2:Win32_BIOS
Properties            : {BiosCharacteristics, BIOSVersion, BuildNumber, Caption...}
SystemProperties      : {__GENUS, __CLASS, __SUPERCLASS, __DYNASTY...}
Qualifiers            : {dynamic, Locale, provider, UUID}
Site                  :
Container             :

Variable Properties and Methods

PS E:\ > $string | get-Member

   TypeName: System.String

Name             MemberType            Definition
----             ----------            ----------
Clone            Method                System.Object Clone()
CompareTo        Method                int CompareTo(System.Object value), int CompareTo(string strB)
Contains         Method                bool Contains(string value)
CopyTo           Method                System.Void CopyTo(int sourceIndex, char[] destination, int destinationIndex,...
EndsWith         Method                bool EndsWith(string value), bool EndsWith(string value, System.StringCompari...
Equals           Method                bool Equals(System.Object obj), bool Equals(string value), bool Equals(string...
GetEnumerator    Method                System.CharEnumerator GetEnumerator()
ToString         Method                string ToString(), string ToString(System.IFormatProvider provider)
ToUpper          Method                string ToUpper(), string ToUpper(System.Globalization.CultureInfo culture)
ToUpperInvariant Method                string ToUpperInvariant()
Trim             Method                string Trim(Params char[] trimChars), string Trim()
TrimEnd          Method                string TrimEnd(Params char[] trimChars)
TrimStart        Method                string TrimStart(Params char[] trimChars)
Chars            ParameterizedProperty char Chars(int index) {get;}
Length           Property              System.Int32 Length {get;}

It's not uncommon for objects provided by API's to provide methods that are in fact objects themselves, you can end up with a lot of information being available once you're capable of drilling into them.


Checking whether a variable is NULL or not can be problematic. In that the easiest test doesn't always work.

Basic test for whether a variable exists or not, works in most cases...

if (!$var) {
    "Variable is null"

If you expect your variable to be NULL or contain a positive number...

if ($var -gt 0) {
    "Variable is NOT null"

Last resort test...

if ($var.gettype().ToString() -eq "System.DBNull") {
    "Variable is null"


Variables only fully exist within the scope of the script or function within which they are defined. Within functions local copies of a variable are available, but manipulating them has no effect on the real/master variable in the main scope, to get around this you can use script to enforce using the variable that's in the main script's scope...

function Local-Add($text) {
    $List += $text

function Global-Add($text) {
    $script:List += $text

$List = @() 
$List += "Text message ONE"
$List.Length                           # List contains one entry
Local-Add "Text message TWO"
$List.Length                           # List still contains one entry
Global-Add "Text message THREE"
$List.Length                           # List now contains two entries

Similarly, you can create a variable within a function that has global scope...

function Create-Var {
    if (!$TestVar) {
        $script:TestVar = "stuff"
        Write-Host 'Created $TestVar'
    } else {
        Write-Host '$TestVar already exists'

Write-Host '$TestVar contains [' $TestVar ']'

...which when run produces the following output...

Created $TestVar
$TestVar already exists
$TestVar contains [ stuff ]

You can achieve the same result by using the Set-Variable CmdLet with the -Scope parameter instead of script, for example...

function Create-Var {
    if (!$TestVar) {
        #$script:TestVar = "stuff"
        Set-Variable -Name TestVar -Value "stuff" -Scope 1
        Write-Host 'Created $TestVar'
    } else {
        Write-Host '$TestVar already exists'

Write-Host '$TestVar contains [' $TestVar ']'

Macros / Built-in Variables

Variable Description
$_ Variable passed through pipeline from previous command
$? Success/failure of previous statement - see Basic_Error_Handler
$Error Last error - array of recent errors - see $error
$LastExitCode Exit code of the last natively run application
$foreach Enumerator in a foreach loop
$Host Information about the machine being executed on (can also use Get-Host
$args Array of arguments passed to a script - see Script_Arguments

Environment Variable

Environmental variables can be accessed via $env

$env:userprofile                  # User profile (eg C:\Users\joeblogs)
dir env:                          # Show all available variables

For a full list use...

Get-ChildItem env:

...or for some commonly used ones...

Variable Description Example data
APPDATA Application data path C:\Users\RodHull\AppData\Roaming
COMPUTERNAME Local System's hostname LAPTOP-01
LOGONSERVER Domain Controller Logged into DC-SERVER-03
USERDOMAIN Logged in user's domain DOMAIN.COM
USERNAME Local System's hostname rodhull

Pages in category "Variables (PowerShell)"

The following 3 pages are in this category, out of 3 total.