Test if file exists in PowerShell - powershell

Question

I can use Test-Path to check whether the file name entered exists, but I'd like to avoid producing a system error if the user hits RETURN and the input string is blank. I thought the -ErrorAction Common Parameter would do the trick, but this:
$configFile = Read-Host "Please specify a config. file: "
$checkfile = Test-Path $configFile -ErrorAction SilentlyContinue
still produces:
Test-Path : Cannot bind argument to parameter 'Path' because it is an empty string.
At C:\Scripts\testparm2.ps1:19 char:31
+ $checkfile = Test-Path <<<< $configFile -ErrorAction SilentlyContinue
+ CategoryInfo : InvalidData: (:) [Test-Path], ParameterBindingValidationException
+ FullyQualifiedErrorId : ParameterArgumentValidationErrorEmptyStringNotAllowed,Microsoft.PowerShell.Commands.TestPathCommand
Do I have to check that the string isn't blank or NULL explicitly?
I'm using PowerShell v2.0

Answer 1

You can do something like this:
$checkfile = if ("$configFile") {
Test-Path -LiteralPath $configFile
} else {
$false
}
The double quotes prevent false negatives, e.g. in case you want to test for the existence of a folder named 0.
Another option would be to set $ErrorActionPreference. However, in that case you need to cast the result of Test-Path to a boolean value, because although the exception is suppressed the cmdlet still doesn't return a result. Casting that $null "return value" to bool produces $false.
$oldEAP = $ErrorActionPreference
$ErrorActionPreference = 'SilentlyContinue'
$checkfile = [bool](Test-Path -LiteralPath $configFile)
$ErrorActionPreference = $oldEAP

Answer 2

Yes, you have to check explicitly for string null or empty:
$configFile = Read-Host "Please specify a config. file: "
if ([string]::IsNullOrEmpty($configFile))
{
$checkfile = $false
}
else
{
$checkfile = Test-Path $configFile -ErrorAction SilentlyContinue
}
Or use try/catch:
$configFile = Read-Host "Please specify a config. file: "
if ( $(Try { Test-Path $configFile.trim() } Catch { $false }) )
{
$checkfile = $true
}
else
{
$checkfile = $false
}