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PowerShell Hashtable

Introduction To PowerShell Hashtable

I think of a PowerShell's hashtable as a super array. Whereas arrays are one dimensional, hashtables have multiple keys. Hash tables make it easier to work with the underlying connections and they work on Key = Value pairs.

Topics for PowerShell's Hashtable

Introduction to PowerShell Arrays and Hashtables
Example 1: Simple PowerShell Hashtables
Example 2: Hashtable to List Services That Should Have Started
Summary of PowerShell Hashtable

♣

Introduction to PowerShell Arrays and Hashtables

Before I deal with hashtables, here are some simple array examples.

Array @(Parenthesis)

You could think of an array as a one dimensional hashtable, however, the analogy is not perfect, and is let down by the fact that PowerShell arrays use (parenthesis) whereas hashtables use {braces}.

$CompArr =@("Jasmine", "Louise", "Longhorn")

Note 1: The 'At' symbol (@) is mandatory for introducing both arrays and hashtables.

Hashtable @{Curly Braces}

Hashtables are also know as an associative array, a dictionary, Key = Value pairs.

$GuyHashTable = @{Key = Value pairs}

Note 2: You need that @ 'At' before the curly brackets. While PowerShell normally uses -eq, hashtables require the old fashioned = sign between the key and its value. Most hashtables will have multiple keys, these are separated by semi-colons (;).

Example 1: Simple PowerShell Hashtables

# Simple PowerShell Hashtable
$CompHash = @{Jasmine ="Win7"; Louise="Vista"}

Note 3: By assigning the hashtable to a variable you can access the value of individual keys. Naturally, this is more useful where you have lots of Key = Value pairs.

Example 1b: Interrogating the Hashtable

# PowerShell Hashtable Example
$CompHash = @{Jasmine ="Win7"; Louise="Vista"; Mary="XP"}
$CompHash.Louise
Write-Host "There are" $CompHash.count "keys"

Note 4: In addition to accessing the value by its $variable.key, you can return a count of all the keys.

Example 1c: A Hashtable Featuring Books

# PowerShell Hash table
Clear-Host
$Book = @{ISBN = 1843560295 ; title = "Lost"; author = "Guy, Thomas" }

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Example 2: PowerShell -AsHashTable to List Services That Should Have Started

The purpose of this real-life hashtable example is to identify which Windows services are set to Auto start, but are in fact stopped. -AsHashTable is a parameter of Group-Object.

# PowerShell -AsHashTable with Windows services
Clear-Host
$HashService = Get-WmiObject Win32_Service | Group-Object State -AsHashTable
$HashService.Stopped | Where {$_.StartMode -eq "Auto"} `
| Format-Table Name, StartMode, State -auto

Note 5: This example uses Group-Object's -AsHashTable parameter to leverage data supplied by WMI.

Note 6: See more on the use of PowerShell's $_ variable.

Example 3: Get-WinEvent -FilterHashTable

Get-WinEvent has a -FilterHashTable parameter so that you can refine the output. Example 3 shows how to filter on just two properties, it would be easy to add more criteria.

Clear-Host
Get-WinEvent -MaxEvents 100 -FilterHashtable @{logname="System"; ID="50036"}

Note 7: The syntax has a few surprises; a) There is no hypen before the parameter. b) It uses the = (equals sign) and not -eq. Also remember the overall PowerShell hashtable format @{Filter="criteria"}.

See more on PowerShell Event Logs

Summary of PowerShell Hashtable

It's the 'At' that introduces a hashtable. Whereas arrays are one dimensional, hashtables can have multiple keys. Hashtables make it easier to work with the underlying connections and they work on Key = Value pairs.

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See more PowerShell examples for syntax advice

• PowerShell Tutorials • Syntax • PowerShell functions • Plist

• Get-Date • Quotes • PowerShell variables • RegEx

• Conditional operators • Hashtable • Windows PowerShell

Please email me if you have a better example script. Also please report any factual mistakes, grammatical errors or broken links, I will be happy to correct the fault.

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