Ternary operator in PowerShell

mguassa Source

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?

powershellternary-operator

Answers

answered 3 years ago mjolinor #1

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

. ({'condition is false'},{'condition is true'})[$condition]

answered 3 years ago Vesper #2

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

[email protected]("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.

answered 2 years ago sodawillow #3

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

answered 2 years ago Edward Brey #4

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})

answered 2 years ago Garrett Serack #5

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" 

answered 2 years ago fbehrens #6

$result = If ($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"}) 

answered 8 months ago JohnLBevan #7

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')

answered 7 months ago iRon #8

PowerShell currently doesn'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)

answered 1 month ago nudl #9

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"

answered 2 weeks ago FatBrioche #10

You can use :

$var = q(condition) ? condtion_is_true : condition_is_false

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