Ternary operator in PowerShell

271
votes

From what I know, PowerShell doesn't seem to have a built-in expression for the so-called ternary operator.

For example, in the C language, which supports the ternary operator, I could write something like:

<condition> ? <condition-is-true> : <condition-is-false>;

If that doesn't really exist in PowerShell, what would be the best way (i.e. easy to read and to maintain) to accomplish the same result?

14
powershellternary-operatorconditional-operator
Take a look at github.com/nightroman/PowerShellTraps/tree/master/Basic/… . If this is what you are looking for I can make it an answer. – Roman Kuzmin
It's a conditional operator or ternary if. It's not "the ternary operator" since all that means is a operator (any operator) that takes three arguments. – Damien_The_Unbeliever
@Damien_The_Unbeliever That's technically true, but it's often called ternary operator. "Since this operator is often the only existing ternary operator in the language, it is sometimes simply referred to as "the ternary operator". In some languages, this operator is referred to as "the conditional operator." Ternary operation – mguassa
Visual basic does not have a true ternary operator but considers the IF and IFF to be functionally equivelent. – Matt
The ternary operator was added to native PowerShell in version 7. Added an answer accordingly. – Trevor Sullivan

14 Answers

386
votes
$result = If ($condition) {"true"} Else {"false"}

Everything else is incidental complexity and thus to be avoided.

For use in or as an expression, not just an assignment, wrap it in $(), thus:

write-host  $(If ($condition) {"true"} Else {"false"})
77
votes

The closest PowerShell construct I've been able to come up with to emulate that is:

@({'condition is false'},{'condition is true'})[$condition]
67
votes

Powershell 7 has it. https://toastit.dev/2019/09/25/ternary-operator-powershell-7/

PS C:\Users\js> 0 ? 'yes' : 'no'
no
PS C:\Users\js> 1 ? 'yes' : 'no'
yes
24
votes

Per this PowerShell blog post, you can create an alias to define a ?: operator:

set-alias ?: Invoke-Ternary -Option AllScope -Description "PSCX filter alias"
filter Invoke-Ternary ([scriptblock]$decider, [scriptblock]$ifTrue, [scriptblock]$ifFalse) 
{
   if (&$decider) { 
      &$ifTrue
   } else { 
      &$ifFalse 
   }
}

Use it like this:

$total = ($quantity * $price ) * (?:  {$quantity -le 10} {.9} {.75})
22
votes

I too, looked for a better answer, and while the solution in Edward's post is "ok", I came up with a far more natural solution in this blog post

Short and sweet:

# ---------------------------------------------------------------------------
# Name:   Invoke-Assignment
# Alias:  =
# Author: Garrett Serack (@FearTheCowboy)
# Desc:   Enables expressions like the C# operators: 
#         Ternary: 
#             <condition> ? <trueresult> : <falseresult> 
#             e.g. 
#                status = (age > 50) ? "old" : "young";
#         Null-Coalescing 
#             <value> ?? <value-if-value-is-null>
#             e.g.
#                name = GetName() ?? "No Name";
#             
# Ternary Usage:  
#         $status == ($age > 50) ? "old" : "young"
#
# Null Coalescing Usage:
#         $name = (get-name) ? "No Name" 
# ---------------------------------------------------------------------------

# returns the evaluated value of the parameter passed in, 
# executing it, if it is a scriptblock   
function eval($item) {
    if( $item -ne $null ) {
        if( $item -is "ScriptBlock" ) {
            return & $item
        }
        return $item
    }
    return $null
}

# an extended assignment function; implements logic for Ternarys and Null-Coalescing expressions
function Invoke-Assignment {
    if( $args ) {
        # ternary
        if ($p = [array]::IndexOf($args,'?' )+1) {
            if (eval($args[0])) {
                return eval($args[$p])
            } 
            return eval($args[([array]::IndexOf($args,':',$p))+1]) 
        }

        # null-coalescing
        if ($p = ([array]::IndexOf($args,'??',$p)+1)) {
            if ($result = eval($args[0])) {
                return $result
            } 
            return eval($args[$p])
        } 

        # neither ternary or null-coalescing, just a value  
        return eval($args[0])
    }
    return $null
}

# alias the function to the equals sign (which doesn't impede the normal use of = )
set-alias = Invoke-Assignment -Option AllScope -Description "FearTheCowboy's Invoke-Assignment."

Which makes it easy to do stuff like (more examples in blog post):

$message == ($age > 50) ? "Old Man" :"Young Dude"
22
votes

Try powershell's switch statement as an alternative, especially for variable assignment - multiple lines, but readable.

Example,

$WinVer = switch ( Test-Path "$Env:windir\SysWOW64" ) {
  $true    { "64-bit" }
  $false   { "32-bit" }
}
"This version of Windows is $WinVer"
20
votes

As of PowerShell version 7, the ternary operator is built into PowerShell.

1 -gt 2 ? "Yes" : "No"
# Returns "No"

1 -gt 2 ? 'Yes' : $null
# Get a $null response for false-y return value
10
votes

Since a ternary operator is usually used when assigning value, it should return a value. This is the way that can work:

$var=@("value if false","value if true")[[byte](condition)]

Stupid, but working. Also this construction can be used to quickly turn an int into another value, just add array elements and specify an expression that returns 0-based non-negative values.

6
votes

Since I have used this many times already and didn't see it listed here, I'll add my piece :

$var = @{$true="this is true";$false="this is false"}[1 -eq 1]

ugliest of all !

kinda source

5
votes

I've recently improved (open PullRequest) the ternary conditional and null-coalescing operators in the PoweShell lib 'Pscx'
Pls have a look for my solution.


My github topic branch: UtilityModule_Invoke-Operators

Functions:

Invoke-Ternary
Invoke-TernaryAsPipe
Invoke-NullCoalescing
NullCoalescingAsPipe

Aliases

Set-Alias :?:   Pscx\Invoke-Ternary                     -Description "PSCX alias"
Set-Alias ?:    Pscx\Invoke-TernaryAsPipe               -Description "PSCX alias"
Set-Alias :??   Pscx\Invoke-NullCoalescing              -Description "PSCX alias"
Set-Alias ??    Pscx\Invoke-NullCoalescingAsPipe        -Description "PSCX alias"

Usage

<condition_expression> |?: <true_expression> <false_expression>

<variable_expression> |?? <alternate_expression>

As expression you can pass:
$null, a literal, a variable, an 'external' expression ($b -eq 4) or a scriptblock {$b -eq 4}

If a variable in the variable expression is $null or not existing, the alternate expression is evaluated as output.

4
votes

PowerShell currently doesn't didn't have a native Inline If (or ternary If) but you could consider to use the custom cmdlet:

IIf <condition> <condition-is-true> <condition-is-false>

See: PowerShell inline If (IIf)

2
votes

If you're just looking for a syntactically simple way to assign/return a string or numeric based on a boolean condition, you can use the multiplication operator like this:

"Condition is "+("true"*$condition)+("false"*!$condition)
(12.34*$condition)+(56.78*!$condition)

If you're only ever interested in the result when something is true, you can just omit the false part entirely (or vice versa), e.g. a simple scoring system:

$isTall = $true
$isDark = $false
$isHandsome = $true

$score = (2*$isTall)+(4*$isDark)+(10*$isHandsome)
"Score = $score"
# or
# "Score = $((2*$isTall)+(4*$isDark)+(10*$isHandsome))"

Note that the boolean value should not be the leading term in the multiplication, i.e. $condition*"true" etc. won't work.

2
votes

The ternary operator in PowerShell was introduced with the PowerShell version7.0.

[Condition] ? (output if True) : (output if False)

Example 01

$a = 5; $b = 6
($a -gt $b) ? "True" : "False"

Output

False

Example 02

($a -gt $b) ? ("$a is greater than $b") : ("$a is less than $b")

Output

5 is less than 6

more information https://www.tutorialspoint.com/how-ternary-operator-in-powershell-works

1
votes

Here's an alternative custom function approach:

function Test-TernaryOperatorCondition {
    [CmdletBinding()]
    param (
        [Parameter(ValueFromPipeline = $true, Mandatory = $true)]
        [bool]$ConditionResult
        ,
        [Parameter(Mandatory = $true, Position = 0)]
        [PSObject]$ValueIfTrue
        ,
        [Parameter(Mandatory = $true, Position = 1)]
        [ValidateSet(':')]
        [char]$Colon
        ,
        [Parameter(Mandatory = $true, Position = 2)]
        [PSObject]$ValueIfFalse
    )
    process {
        if ($ConditionResult) {
            $ValueIfTrue
        }
        else {
            $ValueIfFalse
        }
    }
}
set-alias -Name '???' -Value 'Test-TernaryOperatorCondition'

Example

1 -eq 1 |??? 'match' : 'nomatch'
1 -eq 2 |??? 'match' : 'nomatch'

Differences Explained

  • Why is it 3 question marks instead of 1?
    • The ? character is already an alias for Where-Object.
    • ?? is used in other languages as a null coalescing operator, and I wanted to avoid confusion.
  • Why do we need the pipe before the command?
    • Since I'm utilising the pipeline to evaluate this, we still need this character to pipe the condition into our function
  • What happens if I pass in an array?
    • We get a result for each value; i.e. -2..2 |??? 'match' : 'nomatch' gives: match, match, nomatch, match, match (i.e. since any non-zero int evaluates to true; whilst zero evaluates to false).
    • If you don't want that, convert the array to a bool; ([bool](-2..2)) |??? 'match' : 'nomatch' (or simply: [bool](-2..2) |??? 'match' : 'nomatch')