Powershell Catch print modified error only - powershell

Question

I have the csv file with the following values:
User,TimeStamp
Pinky,11/4/2015 5:00
Brain,
Leo,never
Don,unspecified
I want to ensure this file for the TimeStamp column either has a date, or a $null value. To do this I am using the following code:
Function HealthCheckTimeStampColumn
{
Param ($userInputCsvFileWithPath)
Write-Host "Checking if TimeStamp column has invalid values..."
Import-Csv $userInputCsvFileWithPath | %{
if ($_.TimeStamp)
{
Try
{
([datetime]$_.TimeStamp).Ticks | Out-Null
}
Catch [system.exception]
{
$Error.Clear()
$invalidValue = $_.TimeStamp
Write-Error "Invalid Value found `"$_.TimeStamp`"; Value expected Date or `"`""
Exit
}
}
}
Write-Host "All values were found valid."
Write-Host "TimeStamp Healthcheck Column Passed"
Write-Host ""
}
With this code, I get this error:
Invalid Value found "Cannot convert value "never" to type "System.DateTime". Error: "The string was not recognized as
a valid DateTime. There is an unknown word starting at index 0.".TimeStamp"; Value expected Date or ""
At C:\Scripts\Tests\TestTime.ps1:247 char:42
+ Import-Csv $userInputCsvFileWithPath | %{
+ ~
+ CategoryInfo : NotSpecified: (:) [Write-Error], WriteErrorException
+ FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException
If I try this line of code Instead:
Write-Error "Invalid Value found `"$invalidValue`"; Value expected Date or `"`""
I get this error:
Invalid Value found ""; Value expected Date or ""
At C:\Scripts\Tests\TestTime.ps1:247 char:42
+ Import-Csv $userInputCsvFileWithPath | %{
+ ~
+ CategoryInfo : NotSpecified: (:) [Write-Error], WriteErrorException
+ FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException
The error I am expecting to see is this:
Invalid Value found "never"; Value expected Date or ""
At C:\Scripts\Tests\TestTime.ps1:247 char:42
+ Import-Csv $userInputCsvFileWithPath | %{
+ ~
+ CategoryInfo : NotSpecified: (:) [Write-Error], WriteErrorException
+ FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException
Can anyone tell me what I am doing wrong?

Answer 1

You don't really need a try/catch block for this one either. They are good for unexpected and unavoidable errors. However looking about_Type_Operators you will see -as and -is which handle this situation rather gracefully.
-is : Returns TRUE when the input is an instance of the specified .NET Framework type.
-as : Converts the input to the specified .NET Framework type.
When -as encounters a string or something that is not castable to [datetime] it will return a null. More importantly it will not error. I propose that you check all values for non nulls and invalid date times. Capture all of those in a variable. Then check if the variables has any values. Print all at once! and then exit if you want. I also second what user2460798's answer said about the use of exit.
Function HealthCheckTimeStampColumn{
Param ($userInputCsvFileWithPath)
$badRows = Import-Csv $userInputCsvFileWithPath |
Where-Object{-not [string]::IsNullOrEmpty($_.TimeStamp) -and ($_.TimeStamp -as [datetime]) -eq $null}
if($badRows){
$badRows | ForEach-Object{
Write-Host "'$($_.Timestamp)' is not a valid datetime" -ForegroundColor Red
}
Write-Error "$($badRows.Count) Invalid Value(s) found"
} else {
"All values were found valid.","TimeStamp Healthcheck Column Passed","" | Write-Host
}
}

Answer 2

Turning PerSerAl's observation into an answer:
$_ changes meaning from when it is in the foreach-object loop (but outside catch block) to when it is in catchblock. In the first case it is the current object (row), which apparently has the value "never" for its timestamp. But in the catch block it is the errorrecord that was generated as a result of the error. So to fix:
Function HealthCheckTimeStampColumn
{
Param ($userInputCsvFileWithPath)
Write-Host "Checking if TimeStamp column has invalid values..."
Import-Csv $userInputCsvFileWithPath | %{
$row = $_
if ($_.TimeStamp)
{
Try
{
([datetime]$_.TimeStamp).Ticks | Out-Null
}
Catch [system.exception]
{
$Error.Clear()
$invalidValue = $_.TimeStamp
Write-Error "Invalid Value found `"$row.TimeStamp`"; Value expected Date or `"`""
Exit
}
}
}
Write-Host "All values were found valid."
Write-Host "TimeStamp Healthcheck Column Passed"
Write-Host ""
}
BTW, if you want to process the whole file you'll need to remove exit from the catch block.