PowerShell try/catch/finally
I recently wrote a PowerShell script that works great - however, I'd like to now upgrade the script and add some error checking / handling - but I've been stumped at the first hurdle it seems. Why won't the following code work?
try {
Remove-Item "C:\somenonexistentfolder\file.txt" -ErrorAction Stop
}
catch [System.Management.Automation.ItemNotFoundException] {
"item not found"
}
catch {
"any other undefined errors"
$error[0]
}
finally {
"Finished"
}
The error is caught in the second catch block - you can see the output from $error[0]
. Obviously I would like to catch it in the first block. What am I missing?
-ErrorAction Stop
is changing things for you. Try adding this and see what you get:
Catch [System.Management.Automation.ActionPreferenceStopException] {
"caught a StopExecution Exception"
$error[0]
}
That is very odd.
I went through ItemNotFoundException
's base classes and tested the following multiple catch
es to see what would catch it:
try {
remove-item C:\nonexistent\file.txt -erroraction stop
}
catch [System.Management.Automation.ItemNotFoundException] {
write-host 'ItemNotFound'
}
catch [System.Management.Automation.SessionStateException] {
write-host 'SessionState'
}
catch [System.Management.Automation.RuntimeException] {
write-host 'RuntimeException'
}
catch [System.SystemException] {
write-host 'SystemException'
}
catch [System.Exception] {
write-host 'Exception'
}
catch {
write-host 'well, darn'
}
As it turns out, the output was 'RuntimeException'
. I also tried it with a different exception CommandNotFoundException
:
try {
do-nonexistent-command
}
catch [System.Management.Automation.CommandNotFoundException] {
write-host 'CommandNotFoundException'
}
catch {
write-host 'well, darn'
}
That output 'CommandNotFoundException'
correctly.
I vaguely remember reading elsewhere (though I couldn't find it again) of problems with this. In such cases where exception filtering didn't work correctly, they would catch the closest Type
they could and then use a switch
. The following just catches Exception
instead of RuntimeException
, but is the switch
equivalent of my first example that checks all base types of ItemNotFoundException
:
try {
Remove-Item C:\nonexistent\file.txt -ErrorAction Stop
}
catch [System.Exception] {
switch($_.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.