Safely converting string to bool in PowerShell

You could use a try / catch block:

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

Gives:

> $result
False

Another possibility is to use the switch statemement and only evaluate True, 1 and default:

$a = "Bla"
$ret = switch ($a) { {$_ -eq 1 -or $_ -eq  "True"}{$True} default{$false}}

In this if the string equals to True $true is returned. In all other cases $false is returned.

And another way to do it is this:

@{$true="True";$false="False"}[$a -eq "True" -or $a -eq 1]

Source Ternary operator in PowerShell by Jon Friesen

$a = 'bla'
$a = ($a -eq [bool]::TrueString).tostring()
$a

False

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"
}