Null coalescing in powershell

by

Powershell 7+

Powershell 7 introduces native null coalescing, null conditional assignment, and ternary operators in Powershell.

Null Coalescing

$null ?? 100    # Result is 100

"Evaluated" ?? (Expensive-Operation "Not Evaluated")    # Right side here is not evaluated

Null Conditional Assignment

$x = $null
$x ??= 100    # $x is now 100
$x ??= 200    # $x remains 100

Ternary Operator

$true  ? "this value returned" : "this expression not evaluated"
$false ? "this expression not evaluated" : "this value returned"

Previous Versions:

No need for the Powershell Community Extensions, you can use the standard Powershell if statements as an expression:

variable = if (condition) { expr1 } else { expr2 }

So to the replacements for your first C# expression of:

var s = myval ?? "new value";

becomes one of the following (depending on preference):

$s = if ($myval -eq $null) { "new value" } else { $myval }
$s = if ($myval -ne $null) { $myval } else { "new value" }

or depending on what $myval might contain you could use:

$s = if ($myval) { $myval } else { "new value" }

and the second C# expression maps in a similar way:

var x = myval == null ? "" : otherval;

becomes

$x = if ($myval -eq $null) { "" } else { $otherval }

Now to be fair, these aren’t very snappy, and nowhere near as comfortable to use as the C# forms.

You might also consider wrapping it in a very simple function to make things more readable:

function Coalesce($a, $b) { if ($a -ne $null) { $a } else { $b } }

$s = Coalesce $myval "new value"

or possibly as, IfNull:

function IfNull($a, $b, $c) { if ($a -eq $null) { $b } else { $c } }

$s = IfNull $myval "new value" $myval
$x = IfNull $myval "" $otherval

As you can see a very simple function can give you quite a bit of freedom of syntax.

UPDATE: One extra option to consider in the mix is a more generic IsTrue function:

function IfTrue($a, $b, $c) { if ($a) { $b } else { $c } }

$x = IfTrue ($myval -eq $null) "" $otherval

Then combine that is Powershell’s ability to declare aliases that look a bit like operators, you end up with:

New-Alias "??" Coalesce

$s = ?? $myval "new value"

New-Alias "?:" IfTrue

$ans = ?: ($q -eq "meaning of life") 42 $otherval

Clearly this isn’t going to be to everyone’s taste, but may be what you’re looking for.

As Thomas notes, one other subtle difference between the C# version and the above is that C# performs short-circuiting of the arguments, but the Powershell versions involving functions/aliases will always evaluate all arguments. If this is a problem, use the if expression form.

More Related Contents:

  1. String handling from Powershell script
  2. How to create a zip archive with PowerShell?
  3. Use PowerShell to run virus scan on multiple servers
  4. Unable to access UNC Paths in Powershell remote session
  5. PowerShell IE9 ComObject has all null properties after navigating to webpage
  6. PowerShell script to check an application that’s locking a file?
  7. Lambda Expression in Powershell
  8. save PSCredential in the file
  9. How do I write a PowerShell script that accepts pipeline input?
  10. PowerShell’s Invoke-RestMethod equivalent of curl -u (Basic Authentication)
  11. How do I Start a job of a function i just defined?
  12. Create directory if it does not exist
  13. PowerShell – get process ID of called application
  14. Delete all files and folders but exclude a subfolder
  15. Start-Process with PowerShell.exe exhibits different behavior with embedded single quotes and double quotes
  16. Can the following Nested foreach loop be simplified in PowerShell?
  17. Add Write-Progress to Get-Job/Wait-Job
  18. Powershell with exchange– How do I append all verbose output to a file
  19. How to handle command-line arguments in PowerShell
  20. How to send email with PowerShell
  21. How to split string by string in Powershell
  22. Powershell: Colon in commandlet parameters
  23. Passing PowerShell variables into a script block
  24. Why is $false -eq “” true?
  25. In Powershell what is the idiomatic way of converting a string to an int?
  26. PowerShell is missing the terminator: “
  27. Using PowerShell to remove lines from a text file if it contains a string
  28. How to execute a PowerShell script only before a web deploy Publish task in VS 2012?
  29. Jenkins powershell plugin is running 32 bit Powershell and I need 64bit
  30. Pass function as a parameter

Leave a Comment