Powershell switch type parameters

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Copied from msgoodies blog, thanks.

http://msgoodies.blogspot.hk/2006/12/negating-powershell-switch-parameters.html


Below examples should tell it all.


set-psdebug -trace 1
# f1 is a normal function with a switch parameter


function f1([switch] $showOutput) {
 if ($showOutput.isPresent) {
  "f1"
 }
}


# f2 is a function with a switch parameter defaulted to present
function f2([switch] $showOutput=[switch]::present) {
 if ($showOutput.isPresent) {
  "f2"
 }
}




# f3 is a function with a switch parameter defaulted to true, this gives the same result
# as using [switch]::present
function f3([switch] $showOutput=$true) {
 if ($showOutput.isPresent) {
  "f3"
 }
}


# run f1, no output shown
f1
# run f1, show output
f1 -showOutput


# run f2, show output
f2


# run f2, show output
f2 -showOutput


# run f2, no output
f2 -showOutput:$false


# run f3, same behavior as f2
f3
f3 -showOutput
f3 -showOutput:$false


# Show the acceptable values for a switch parameter
f2 -showOutput:no
# f2 : Cannot convert value "System.String" to type "System.Management.Automation.SwitchParameter",
# parameters of this type only accept booleans or numbers, use $true, $false, 1 or 0 instead.
# At line:1 char:16
# + f2 -showOutput:n <<<< o


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