An error in a PowerShell script will prevent it from completing script execution successfully. Using error handling with try-catch blocks allows you to manage and respond to these terminating errors. In this post, we will discuss the basics of try/catch blocks and how to find or handle Custom Error Message in PowerShell.
Handling errors effectively in scripts can save a lot of troubleshooting time and provide better user experiences. In PowerShell, we have robust options to handle exceptions using try, catch, and finally blocks. Let’s dive into how you can use try-catch to gracefully handle errors and add custom error messages for better feedback.
Why Use Exception Handling in PowerShell?
Scripts can fail for many reasons: missing files, invalid input, or network issues, to name a few. With exception handling, you can capture these issues, inform users in a friendly way, and potentially recover from errors without crashing your script. Using try-catch, you can:
- Catch specific errors.
- Display user-friendly messages.
- Log errors for debugging.
Syntax overview of Try/Catch
Like similar in other programming languages, the try-catch block syntax is very simple and syntax will be the same. It is framed with two sections enclosed in curly brackets (the first block is a try and the second is the catch block).
try {
# Functionality within try block
}
catch {
# Action to do with errors
}
The main purpose of using the try-catch block, we can start to manipulate the error output and make it more friendly for the user.
Example 1:
After executing the below script, the below error will be shown on the screen as output and it would occupy some space and the problem may not be immediately visible to the User. So you can use a try-catch block to manipulate the error output and make it more friendly.
without Try-Catch block
Get-content -Path “C:\dotnet-helpers\BLOG\TestFiled.txt”
with Try Catch block
In the below script, we added the ErrorAction parameter with a value of Stop to the command. Not all errors are considered “terminating”, so sometimes we need to add this bit of code in order to properly terminate into the catch block.
try {
Get-content -Path “C:\dotnet-helpers\BLOG\TestFile.txt” -ErrorAction Stop
}
catch {
Write-Warning -Message “Can’t read the file, seem there is an issue”}
Example 2:
Using the $Error Variable
In Example 1, we have displayed our own custom message instead of this you can display the specific error message that occurred instead of the entire red text exception block. When an error occurs in the try block, it is saved to the Automatic variable named $Error. The $Error variable contains an array of recent errors, and you can reference the most recent error in the array at index 0.
try{
Get-content -Path “C:\dotnet-helpers\BLOG\TestFiled.txt” -ErrorAction Stop
}
Catch{Write-Warning -Message “Cant’t read the file, seem there is an issue”
Write-Warning $Error[0]}
Example 3:
Using Exception Messages
You can also use multiple catch blocks in case if you want to handle different types of errors. For this example, we going to handle two different types of errors and planned to display different custom messages. The first CATCH is to handle if the path does not exist and the next CATCH is to handle if any error related to the driver not found.
Using try/catch blocks gives additional power in handling errors in a script and we can have different actions based on the error type. The catch block focuses on not only displaying error messages but we can have logic that will resolve the error and continue executing the rest of the script.
In this example, the file mentioned driver (G:\dotnet-helpers\BLOG\TestFiled.txt) does not exist in the execution machine, so it was caught by [System.Management.Automation.DriveNotFoundException] and executed the same CATCH block.
try{
Get-content -Path "G:\dotnet-helpers\BLOG\TestFiled.txt" -ErrorAction Stop
}
# It will execute if a specific file is not found in a specific Directory
Catch [System.IO.DirectoryNotFoundException] {
Write-Warning -Message "Can't read the file, seems there is an issue"
Write-Warning $Error[0]
}
# It will execute if the specified driver is not found in the specified path
Catch [System.Management.Automation.DriveNotFoundException]{
Write-Warning -Message "Custom Message: Specific driver is not found"
Write-Warning $Error[0]
}
#Execute for Un-Handled exception - This catch block will run if the error does not match any other catch block exception.
Catch{
Write-Warning -Message "Oops, An un-expected Error Occurred"
#It will return the exception message for the last error that occurred.
Write-host $Error[0].Exception.GetType().FullName
}
OUTPUT
