Enum like switch parameter in PowerShell

Question

I am using switch parameters in my PowerShell script in this fashion.

param(
    [switch] $Word,
    [switch] $Excel,
    [switch] $powerpoint,
    [switch] $v2007,
    [switch] $v2010,
    [switch] $x86,
    [switch] $x64,
)

I am trying to figure out any neat way to have it more enum style. As anyone might guess, I would want the user to choose between word, excel and powerpoint. And between x2007 and v2010.

Is there a neat way to get input params enum style?

I am new to PowerShell. So if this sounds like that I don't know something obvious, then please point me to some link where I can read about it.

Igor Popov · Accepted Answer · 2017-07-11 07:30:08Z

122

I would use a ValidateSet parameter attribute instead.

From: about_Functions_Advanced_Parameters

The ValidateSet attribute specifies a set of valid values for a parameter or variable. Windows PowerShell generates an error if a parameter or variable value does not match a value in the set.

Example function:

function test-value
{
    param(
        [Parameter(Position=0)]
        [ValidateSet('word','excel','powerpoint')]
        [System.String]$Application,

        [Parameter(Position=1)]
        [ValidateSet('v2007','v2010')]
        [System.String]$Version
    )


    write-host "Application: $Application"
    write-host "Version: $Version"
}   


PS > test-value -application foo

Output:

test-value : Cannot validate argument on parameter 'Application'. The argument "foo" does not belong to the set "word,excel,powerpoint" specified by the ValidateSet attribute. Supply an argument that is in the set and then try the command again.

edited Jul 11, 2017 at 7:30

Igor Popov

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answered Sep 17, 2010 at 21:10

Shay Levy

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4 Comments

Keith Hill Over a year ago

This approach forces you into using advanced functions which isn't always desirable. You also don't get any form of auto-completion on the enum values. OTOH you don't have to put the enum evaluation within parens e.g. [MyEnum]::A. So, a mixed bag I guess. :-)

Shay Levy Over a year ago

Thanks Keith. On the other hand the function needs to implement various parameter checks to find if more than one switch params was specified. BTW, aren't we all using PowerShell v2 :)

JasonMArcher Over a year ago

Keith, you get tab expansion on ValidateSet if you use PowerTab... just sayin. ;)

Brian Dukes Over a year ago

You do get tab expansion for sets, now (testing in Windows 8.1, in both Powershell 3.0 & 4.0, but not 2.0)

George Howarth · Accepted Answer · 2010-09-17 21:10:04Z

You can use the ValidateSet attribute:

function My-Func
{
    param (
        [Parameter(Mandatory = $true)]
        [ValidateNotNullOrEmpty()]
        [ValidateSet('Word', 'Excel', 'PowerPoint', 'v2007', 'v2010', 'x86', 'x64')]
        [String]$MyParam
    )

    Write-Host "Performing action for $MyParam"
}

My-Func -MyParam 'Word'
My-Func -MyParam 'v2007'
My-Func -MyParam 'SomeVal'

Output:

Performing action for Word
Performing action for v2007
My-Func : Cannot validate argument on parameter 'MyParam'. The argument "SomeVal" does not belong to the set "Word,Excel,PowerPoint,v2007,v2010,x86,x64" specified by the ValidateSet attribute. Supply an argument that is in the
 set and then try the command again.
At C:\Users\George\Documents\PowerShell V2\ValidateSetTest.ps1:15 char:17
+ My-Func -MyParam <<<<  'SomeVal'
    + CategoryInfo          : InvalidData: (:) [My-Func], ParameterBindingValidationException
    + FullyQualifiedErrorId : ParameterArgumentValidationError,My-Func

x0n · Accepted Answer · 2010-09-17 20:18:37Z

10

This blog post by the PowerShell team defines how to do this in PowerShell 1.0. In PowerShell 2.0 you can use Add-Type like so:

C:\PS> Add-Type -TypeDefinition @'
>> public enum MyEnum {
>> A,
>> B,
>> C,
>> D
>> }
>> '@
>>

Update: Here's how to use the enum:

C:\PS> function foo([MyEnum]$enum) { $enum }
C:\PS> foo ([MyEnum]::A)
A

You need the parentheses around the argument to parse the argument as a Type. This is required because arguments are treated more or less like strings. Knowing this, you can also pass them enum in a simple string form and powershell will figure it out:

C:\PS> foo A
A
C:\PS> $arg = "B"
C:\PS> foo $arg
B
C:\PS> foo F
error*

error - F is not one of the enumerated values - valid values include A,B,C,D *

edited Sep 17, 2010 at 20:18

x0n

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answered Sep 17, 2010 at 14:35

Keith Hill

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5 Comments

bits Over a year ago

But how can I use these examples of enum for command line "param" purposes?

Jay Bazuzi Over a year ago

an interesting example, but I think it's not really useful in this case.

Keith Hill Over a year ago

Yeah having to use the parens kind of bites. OTOH I like the tab-completion - next best thing to a true static verification of the enum value. ValidateSet is certainly a nice feature to have in the language, just too bad PowerShell doesn't use that info to drive tab-completion. BTW if it were just one set of choices, you could use switches like the OP uses - just put each switch in separate parameter set and pick one to be the default (if none are specified).

bwerks Over a year ago

For what it's worth, I think it's worth mentioning that using a real enum allows for Get-Help to provide help to script users without making it an opaque runtime minefield. In the example here, Get-Help would show: SYNTAX foo -enum {A | B | C | D}

stib Over a year ago

Tab completion for validate set members seems to work now that we're in the future.

Alex_P · Accepted Answer · 2022-11-01 10:23:13Z

9

Since PowerShell 5 you can actually use/create an Enum natively.

enum OS {
    Windows
    Linux
    iOS
}

This is then also visible as its type.

IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
True     True     OS                                       System.Enum

Maybe a useful link by 4sysops.

To use it in a function, I would either create a separate .psm1 file and add all the enums you need - see my comment which refers to a similiar question - or you can set this enum at the top of your .psm1 file and use in the same file.

For example, I created the file test.psm1 and added this code:

enum OS {
    Windows
    Linux
    iOS
}

function Get-OS {
    param (
        [Parameter(Mandatory)]
        [OS]$os
    )

    Write-Host -Object "The operating system is $os."
    
}

I import the file Import-Module .\test.psm1 and run it:

PS > Get-OS -os Linux
The operating system is Linux.

edited Nov 1, 2022 at 10:23

answered Jun 2, 2020 at 7:09

Alex_P

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2 Comments

Ivo Merchiers Over a year ago

How would you use this in a powershell script as OP asked? Because as far as I know you can't put the enum in front of the initial param call.

Alex_P Over a year ago

@IvoMerchiers, here is a SO question regarding the use of enums in Powershell. stackoverflow.com/questions/62511588/…

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