How to capture error output only in a variable in PowerShell
Here is simpler solution by Simon Wahlin using sub expressions
$output = & $command $params 2>&1
Would be:
$errOutput = $( $output = & $command $params ) 2>&1
You can call the command a slightly different way and use the -ErrorVariable
parameter in PowerShell:
Invoke-Expression "$command $params" -ErrorVariable badoutput
$badoutput
will now contain the contents of the error string.
To add to arco444, the specific exception can be obtained by using $badoutput[0].Exception
.
-ErrorAction and -ErrorVariable has more information on to effectively use the ErrorAction and ErrorVariable parameters built into PowerShell.
Here is the easiest way to show this working:
PS> Stop-Process 13,23
Stop-Process : Cannot find a process with the process identifier 13.
At line:1 char:13
+ Stop-Process <<<< 13,23
Stop-Process : Cannot find a process with the process identifier 23.
At line:1 char:13
+ Stop-Process <<<< 13,23
PS> Stop-Process 13,23 -ErrorAction Stop # Only 1 error
Stop-Process : Command execution stopped because the shell variable “ErrorA
ctionPreference” is set to Stop: Cannot find a process with the process ide
ntifier 13.
At line:1 char:13
+ Stop-Process <<<< 13,23 -ErrorAction Stop # Only 1 error
PS> Stop-Process 13,23 -ErrorAction silentlycontinue # No errors
PS> Stop-Process 13,23 -ErrorAction inquire # ASK
Confirm
Cannot find a process with the process identifier 13.
[Y] Yes [A] Yes to All [H] Halt Command [S] Suspend [?] Help
(default is “Y”):h
Stop-Process : Command execution stopped because the user selected the Halt
option.
At line:1 char:13
+ Stop-Process <<<< 13,23 -ErrorAction inquire # ASK
PS>
PS>
PS> Stop-Process 13,23 -ErrorVariable a -ErrorAction SilentlyContinue
PS> $a[0]
Stop-Process : Cannot find a process with the process identifier 13.
At line:1 char:13
+ Stop-Process <<<< 13,23 -ErrorVariable a -ErrorAction SilentlyContinue
PS> $a[0] |fl * -Force
Exception : Microsoft.PowerShell.Commands.ProcessCommandExcepti
on: Cannot find a process with the process identifi
er 13.
TargetObject : 13
CategoryInfo : ObjectNotFound: (13:Int32) [Stop-Process], ProcessC
ommandException
FullyQualifiedErrorId : NoProcessFoundForGivenId,Microsoft.PowerShell.Comma
nds.StopProcessCommand
ErrorDetails :
InvocationInfo : System.Management.Automation.InvocationInfo
PS> $a |ft TargetObject -force -auto
TargetObject
————
13
23
Now one thing that is not obvious to people is that you can specify a “+” in front of the variable name for ErrorVariable and we will ADD the errors to that variable.
PS> $err=@()
PS> stop-process 13 -ea silentlycontinue -ErrorVariable err
PS> $err.count
1
PS> stop-process 23 -ea silentlycontinue -ErrorVariable +err
PS> $err.count
2
PS> $err
Stop-Process : Cannot find a process with the process identifier 13.
At line:1 char:13
+ stop-process <<<< 13 -ea silentlycontinue -ErrorVariable err
Stop-Process : Cannot find a process with the process identifier 23.
At line:1 char:13
+ stop-process <<<< 23 -ea silentlycontinue -ErrorVariable +err
Lastly, you don’t need to type out –ErrorAction or –ErrorVariable, we have defined parameter aliases for these so you can just type –EA
and -EV
.