SyntaxFix

[powershell] PowerShell try/catch/finally

That is very odd.

I went through ItemNotFoundException's base classes and tested the following multiple catches to see what would catch it:

try {
  remove-item C:\nonexistent\file.txt -erroraction stop
}
catch [System.Management.Automation.ItemNotFoundException] {
  write-host 'ItemNotFound'
}
catch [System.Management.Automation.SessionStateException] {
  write-host 'SessionState'
}
catch [System.Management.Automation.RuntimeException] {
  write-host 'RuntimeException'
}
catch [System.SystemException] {
  write-host 'SystemException'
}
catch [System.Exception] {
  write-host 'Exception'
}
catch {
  write-host 'well, darn'
}

As it turns out, the output was 'RuntimeException'. I also tried it with a different exception CommandNotFoundException:

try {
  do-nonexistent-command
}
catch [System.Management.Automation.CommandNotFoundException] {
  write-host 'CommandNotFoundException'
}
catch {
  write-host 'well, darn'
}

That output 'CommandNotFoundException' correctly.

I vaguely remember reading elsewhere (though I couldn't find it again) of problems with this. In such cases where exception filtering didn't work correctly, they would catch the closest Type they could and then use a switch. The following just catches Exception instead of RuntimeException, but is the switch equivalent of my first example that checks all base types of ItemNotFoundException:

try {
  Remove-Item C:\nonexistent\file.txt -ErrorAction Stop
}
catch [System.Exception] {
  switch($_.Exception.GetType().FullName) {
    'System.Management.Automation.ItemNotFoundException' {
      write-host 'ItemNotFound'
    }
    'System.Management.Automation.SessionStateException' {
      write-host 'SessionState'
    }
    'System.Management.Automation.RuntimeException' {
      write-host 'RuntimeException'
    }
    'System.SystemException' {
      write-host 'SystemException'
    }
    'System.Exception' {
      write-host 'Exception'
    }
    default {'well, darn'}
  }
}

This writes 'ItemNotFound', as it should.

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