PowerShell 3.0 Where Statement

PowerShell 3.0 Where Clause Simplified

PowerShell 3.0 simplifies the 'Where' clause by not requiring either the {curly} brackets or the placeholder $_.xyz.  The benefit is that it makes easier for beginners to write PowerShell scripts.

PowerShell 3.0 Where Examples of the New Syntax

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Example 1: PowerShell v 3.0 Where Example

Scenario: You want to list the dynamic link library files in the Windows System folder.

Example 1a: New Style PowerShell 3.0's Where Syntax

Get-Childitem C:\Windows\System32 | Where extension -eq .dll

Note 1: What's new in PowerShell 3.0 is the simpler syntax
Where extension -eq .dll

Example 1b: Old Style PowerShell 2.0's Where Syntax

In PowerShell 2.0 the above command would require three extra syntax elements: {Curly brackets}, the $_. variable and speech marks around the 'value':

Get-Childitem C:\Windows\System32 | Where {$_.extension -eq '.dll'}

Note 2: I feel a bit of a Philistine because I prefer the full syntax as shown in example 1b.  The shorter method is all very well, but I have found it can cause me confusion and introduce errors.

Example 2: PowerShell 3.0 Where Lists .exe Files

# PowerShell 3.0 'Where' filter for listing .exe in system folder
Clear-Host
Get-ChildItem $Env:WinDir | Where extension -eq .exe

Note 3: $Env:WinDir is an environmental variable, which just get's your Windows folder even if it's on the D:\ and even if you call it WindowsOld.

Challenge: Check the speed of the two techniqes
You can wrap the whole command in Measure-Command and thus compare the speed of the two v2.0 'Where' with the new v3.0 'Where.

Clear-Host
Measure-Command {
Get-ChildItem $Env:WinDir | Where extension -eq .exe
}
Measure-Command {
Get-ChildItem $Env:WinDir | Where-Object {$_.Extension -eq '.exe'}
}

Suggestion: My advice is to run the command 3 or 4 times to make sure caching is causing inconsistent results.

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Example 3: Where Can Still Be Replaced With '?'

You can simplify the filter further by substituting the question mark for the command 'Where', for example: ? extension -eq .exe  (Instead of: Where extension -eq .exe)  The use of the question mark is the same as in PowerShell 2.0, as is the use of the alias gci for Get-ChildItem.

# Windows PowerShell Where script to list exe files C:\Program Files
$FilesExe = gci "C:\Program Files" -recurse
$List = $FilesExe | ? extension -eq .exe
$List | Sort-Object -unique | Format-Table Name, Directory -auto

Learning Points for PowerShell's Where Statement

Note 4: Most people who use PowerShell prefer to type the question mark character '?' instead of 'Where'.  However, I prefer to stick with the full word 'Where' because it makes the script easier to read especially with complex statements.

Note 5: If you like these abbreviations, PowerShell has numerous aliases for common commands, for example in the above script note, gci for Get-ChildItem.  Furthermore, we could employ 'ft' instead of Format-Table.  Even I usually omit the Object from Sort-Object and Where-Object.

Note 6: What I often forget is to introduce the where statement with a pipe, hence,
..... $FilesExe | ? ......  Please learn from my mistake!

Example 4: PowerShell 'Where' Filters WMI Objects

Another situation that benefits from a 'Where' statement is when we research PowerShell's objects.  To take a network example, imagine that our goal is to display the TCP/IP properties, but we have a problem - what is the WMI object called?  Let us begin our quest by researching WMI objects.  We already know that we can use, WmiObject -List, but let us refine our search by adding a where statement.

Where Example 4a

# Windows PowerShell where clause in WMI script
Get-WmiObject -List | Where name -Match Network

Where Example 4b

Once again, we can substitute the question mark for 'Where'; I also added FT to select just the name.

# PowerShell ? (where) filter to list Network WMI objects
Clear-Host
Get-WmiObject -List | ? name -Match Network | FT name

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Researching PowerShell 3.0's Where-Object

PowerShell's where statement is so common that we tend to forget the '?' and even 'Where' are aliases for the Where-Object cmdlet.  The benefit of this realization is that we can call for Get-Help.

Get-Help Where-Object

Both the new 3.0 'Where' and the old v 2.0 version are aliases for the cmdlet Where-Object.

Clear-Host
Get-Help Where-Object -full
# Plain 'help where' also works.

Help reminds us that Where-Object does its filtering by examining a {Scriptblock}.  I have never seen 'where' in isolation, it always receives its input via a pipe (|).

One more point to note, PowerShell uses its own comparison objects such as -gt or -le, and not > or =<.

Where-Object Extra Parameters in PowerShell 3.0

Clear-Host
Get-Command Where-Object | Select -ExpandProperty ParameterSets |
Format-Table Name

Note 7: One of the interesting new parameter in version 3.0 is 'In'.  For example try:
2 -In 1..10

PowerShell 3.0 Where-Object with Get-ChildItem

I am assuming that you can research a cmdlet's properties by appending gm (Get-Member).  For the first experiment we need the 'Extension' property, and later we need LastAccessTime.

Experiment 1: We want a list of the executable (.exe) files in the Windows folder.

Method: We can use PowerShell 3.0's simple 'Where' clause.

# PowerShell 3.0 Get-Childitem Where
Get-Childitem C:\Windows | Where Extension -eq .exe

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Problem with PowerShell 3.0's Where Clause

Following the previous example you would think that | Where LastTime.Year -gt 2012 would provide a list of files that were accessed after 1/1/2013, but it doesn't.

# PowerShell 3.0 Where Problem
Get-Childitem C:\Windows\System | Where LastAccessTime.Year -gt 2012

Although the above example completes without error it does not display any files.  Just in case there are no files, change -gt to -lt, still no files appear.

Solution:  Revert to the PowerShell 2.0 Where syntax.  Remember the full syntax: Curly brackets}, $_. variable, and 'single speech mark'.

# PowerShell 3.0 Where Clause Problem
Get-Childitem C:\Windows\System | Where {$_.LastAccessTime.Year -gt '2012' }

Other PowerShell Cmdlets Containing 'Object'

Clear-Host
Get-Command -Noun object

Summary of The New PowerShell 3.0 'Where' Clause

PowerShell 3.0 simplifies the syntax of the 'Where' statement.  We no longer need either the {curly} brackets or the placeholder $_.xyz.  As a result it's easier for beginners to learn PowerShell, and it's easier for everyone to understand 'Where' clauses.

See more examples of PowerShell's 'Where' clause in action:

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See more Microsoft PowerShell tutorials

PowerShell Tutorials  • Methods  • Cmdlets  • PS Snapin  • Profile.ps1  • Exchange 2007

Command & Expression Mode  • PowerShell pipeline (|)  • PowerShell 'where'  • PowerShell 'Sort'

Windows PowerShell Modules  • Import-Module  • PowerShell Module Directory 

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