Catching errors from external command - powershell

Question

If I running this function (with out try..catch):
executezipFullBackup -PathFileLocation "Z:\" -PathSaveBackup "E:\" -NameOfBackup "MyNASStorage"
PoweShell give me this error:
sz :
At C:\PowerShellF\zipFunction.ps1:6 char:9
+ sz a -t7z "$PathSaveBackup\$NameOfBackup" "$PathFileLocation" #backup
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:String) [], RemoteException
+ FullyQualifiedErrorId : NativeCommandError
ERROR:
Duplicate filename on disk:
BackupTest\private\103.tmp\usr\bin\mail
BackupTest\private\103.tmp\usr\bin\Mail
And that error is OK for me, because I know what is wrong on this step.
But my problem is, if I put this script in try..catch, I dont get this error.
Example:
$ErrorActionPreference = "Stop"; #this is for Try Catch
try {
zipFullBackup -PathFileLocation "$PathFileLocation" -PathSaveBackup "$PathSaveBackup" -NameOfBackup "$NameOfBackup"
} catch {
$MyError = ($Error[0] | Out-String);
Write-Host "$MyError"
}
I get error like this:
sz :
At C:\PowerShellF\zipFunction.ps1:6 char:9
+ sz a -t7z "$PathSaveBackup\$NameOfBackup" "$PathFileLocation" #backup
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:String) [], RemoteException
+ FullyQualifiedErrorId : NativeCommandError
This error is not enough for me, because I don't see ERROR! I don't see this:
ERROR:
Duplicate filename on disk:
BackupTest\private\103.tmp\usr\bin\mail
BackupTest\private\103.tmp\usr\bin\Mail
How can I get try..catch to display this error?

Answer 1

That error message is not part of a PowerShell error/exception, but a message 7zip itself prints to STDOUT. Therefore it can't be caught with a try..catch block, not even if you set $ErrorActionPreference = 'Stop'.
What you can do is collect the command output in a variable, though:
$msg = zipFullBackup ...

Answer 2

The solution for your question is to add the 7zip option -bse1
& cmd.exe /c 'C:\"Program Files"\7-Zip\7z.exe a "c:\DestinationFolder\NameOnZipFiles" c:\FolderToZip\* -bse1
But a better solution for this is to take out the 7zip %errorlevel% from batch, because 7zip is not a PowerShell command.
To do so, use the following code in powershell. Yes the errorlevel variable needs to be written with !errorlevel!
[int]$7zipError=& cmd.exe /v /c 'C:\"Program Files"\7-Zip\7z.exe a -mx0 "c:\DestinationFolder\NameOnZipFiles" c:\FolderToZip\* -bso0 -bsp0 -bse0 &echo:!errorlevel!'
if ($7zipError -gt 0)
{
Write-Host "Errorlevel: $($errorlevel)"
#0 No error
#1 Warning (Non fatal error(s)). For example, one or more files were locked by some other application, so they were not compressed.
#2 Fatal error
#7 Command line error
#8 Not enough memory for operation
#255 User stopped the process
}
If you want to know more and why you need to use “cmd.exe /v” I have written more about this in
PowerShell, only "> $out" catch full error of failed 7Zip extract, why?