Safely converting string to bool in PowerShell

Question

I'm trying to convert an argument of my PowerShell script to a boolean value. This line

[System.Convert]::ToBoolean($a) 

works fine as long as I use valid values such as "true" or "false", but when an invalid value, such as "bla" or "" is passed, an error is returned. I need something akin to TryParse, that would just set the value to false if the input value is invalid and return a boolean indicating conversion success or failure. For the record, I tried [boolean]::TryParse and [bool]::TryParse, PowerShell doesn't seem to recognize it.

Right now I'm having to clumsily handle this by having two extra if statements.

What surprised me that none of the how-to's and blog posts I've found so far deal with invalid values. Am I missing something or are the PowerShell kids simply too cool for input validation?

Answer 1

You could use a try / catch block:

$a = "bla" try {   $result = [System.Convert]::ToBoolean($a)  } catch [FormatException] {   $result = $false } 

Gives:

> $result False 

Answer 2

TryParse should work as long as you use ref and declare the variable first:

$out = $null if ([bool]::TryParse($a, [ref]$out)) {     # parsed to a boolean     Write-Host "Value: $out" } else {     Write-Host "Input is not boolean: $a" }