PowerShell and the “missing” ternary operator


People switching to PowerShell from other languages like JavaScript or C# might be looking for a ternary operator at one point. While there is no built-in ternary operator in PowerShell it is not too hard to come up with something that comes pretty close to it. Let’s look at an example:

filter Get-FourthLetter{
    if ($_.Length -gt 3){
'Pete', 'Joe', 'Dirk' | Get-FourthLetter

This defines a (admittedly pretty useless) filter (like a function but with a process block only) to get the fourth letter of any word that is “piped” into the filter, which has more than 4 characters or -1 (in case the word has less than 4 chars). Let’s try to re-write this with “something like” a ternary operator in PowerShell:

filter Get-FourthLetter{
    (-1, $_[3])[$_.Length -gt 3]
'Pete', 'Joe', 'Dirk'  | Get-FourthLetter

Here we replace the if/else construct with a simple array construct of the form (FALSEEXPRESSION, TRUEEXPRESSION). The CONDITION part is then used to index into the array by making use of the fact that $true evaluates to 1 and $false to 0 in PowerShell. To increase the “uselessness” factor even further, let’s wrap the “ternary” operator functionality into a more generic filter:

filter ?:($trueExpression, $falseExpression){
    ($falseExpression, $trueExpression)[$_]
'Pete', 'Joe', 'Dirk'  | % { ($_.Length -gt 3)  | ?: $_[3] -1 }

I hope this will help anyone that has been desperately searching for a PowerShell ternary operator ;-).


photo credit: Purple storm. Old Jacarandas avenue in Goodna, near Brisbane via photopin (license)


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