PowerShell Try Catch Finally

In this tutorial we will see about PowerShell Try Catch Finally. We will see what it does and some example on how we are able to use it. It is used to handle and respond to terminating errors. When a terminating error occurs, Windows PowerShell will stop running a script or function if there is no error handling. Try Catch Finally consisted by three blocks where statements exist in them.

Try

Try block is used to monitor the statements within, for any errors. If a terminating error will occur on any of the statements in Try block, Windows PowerShell will try to find a Catch block or Trap that matches the specific error in order to respond. The error is saved in $Error variable by default. If no Catch block or Trap is found for error handling, Finally block will run and then the error will be written to the error stream.

Syntax:

try {<statement list>}

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Catch

If there is a Catch block to handle the error, then the statements within the Catch block will run. You can define which errors to be handled by a Catch block. You are allowed to have multiple Catch blocks, so you are able to handle each error a differently. You are allowed to not include any Catch statement in a Try statement. Instead of a Catch block you can use Trap to handle errors.

Syntax:

catch [[<error type>][',' <error type>]*] {<statement list>}

If you would like to know which error types are loaded on your system, in order to specify which errors to be handled by each Catch block, you need to run the below code.

Code:

([appdomain]::CurrentDomain.GetAssemblies() |
    Where-Object {$_.Location -ne $null} |
        foreach {$_.GetExportedTypes() |
            Where-Object {$_.Fullname -match 'Exception'}}).FullName

Output:

The above code will provide you with the full name of all exceptions loaded in your system. When I run it on my system it gave me 341 error types. This depends on what you have loaded.

If you want to refer to the error, within the Catch block, you are able to use $_ or $PSItem. There are also methods to use for re-throwing an error such as:

• Write-Error
• $PSCmdlet.WriteError()
• Throw
• $PSCmdlet.ThrowTerminatingError() 

I am not going into more details about this now. A separate post will be at a later stage only related to errors. I really good post from Kevin Marquette on his blog will give you more information for now. You can find it here.

https://kevinmarquette.github.io/2017-04-10-Powershell-exceptions-everything-you-ever-wanted-to-know/#write-error–erroraction-stop

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Finally

Catch block is followed by Finally block. Finally block is used to free any resources that are no longer needed by your script, as mentioned in Microsoft. Finally block will run before terminating a script or block. It will run even if you hit CTRL+C or use Exit keyword in Catch block. As CTRL+C terminates the pipeline, if you have anything to display on the screen in Finally block it will not be shown, although the Finally block will run.

Syntax:

finally {<statement list>}

Now lets see few examples on how we are able to use Try Catch Finally to help you understand better.

Example 1

In this example we are using only one Catch block along with the try statement. The Catch block in this case, as we have not defined any specific error to handle, it will handle all type of error that might occur in Try block. In the first part the command is correct so we are not receiving any error and the date is displayed. At the second part where the command is wrong, instead of getting the current date or the error that the command does not exist, we will get the output from Catch block.

Code:

try{Get-Date}
catch{"There is an error in Try block"}
try{Get-Dates}
catch{"There is an error in Try block"}

Output:

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Example 2

In this example we will user two Catch blocks in the same Try statement. The first Catch block will be used in case of “Command not found” error only. In there is such error it will display on the screen “There is no such command”. For all other errors, the second Catch block will run and it will display “There is an error in Try block” on the screen. In the first part we are using a command that does not exists so the first catch block will run. At the second part the parameter is used incorrectly. In this case the error is different and the second catch block will run.

Code:

try{Get-Dates}
catch [System.Management.Automation.CommandNotFoundException]
{"There is no such command"}
catch{"There is an error in Try block"}
try{Get-Date -Date}
catch [System.Management.Automation.CommandNotFoundException]
{"There is no such command"}
catch{"There is an error in Try block"}

Output:

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Example 3

In this example we will use also a finally block.

Code:

try{Get-Date}
catch{"There is an error in Try block"}
finally{"Finally block is running"}
try{Get-Dates}
catch [System.Management.Automation.CommandNotFoundException]
{"There is no such command"}
catch{"There is an error in Try block"}
finally{"Finally block is running"}
try{Get-Date -Date}
catch [System.Management.Automation.CommandNotFoundException]
{"There is no such command"}
catch{"There is an error in Try block"}
finally{"Finally block is running"}

Output:

I hope the tutorial about PowerShell Try Catch Finally is helpful.

Please let me know your comments and thoughts.

You feedback is appreciated.

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Related Links:

• PowerShell Tutorials
• PowerShell Scripts
• about_Try_Catch_Finally | Microsoft Docs
• Get-Date – Microsoft Docs
• Write-Error – Microsoft Docs
• about_Throw | Microsoft Docs
• Where-Object – Microsoft Docs
• about_Foreach | Microsoft Docs
• PowerShell Comparison Operators

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Summary

Article Name

PowerShell Try Catch Finally

Description

PowerShell Try Catch Finally. In this tutorial you will find information about PowerShell Try Catch Finally and their use. Stephanos Constantinou Blog

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Stephanos

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Stephanos Constantinou Blog

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