Error logging patterns in PowerShell - Mini Project: Build & Apply

Error Logging Patterns in PowerShell

📖 Scenario: You are managing a PowerShell script that runs several commands. You want to capture errors in a structured way to help troubleshoot issues later.

🎯 Goal: Build a PowerShell script that runs commands, logs errors into a dictionary with error messages and counts, and then displays the error summary.

📋 What You'll Learn

Create a dictionary to store error messages and their counts

Add a variable to hold the list of commands to run

Run each command and catch errors, updating the dictionary

Print the error summary with messages and counts

💡 Why This Matters

🌍 Real World

Scripts often run multiple commands where some may fail. Logging errors helps track and fix issues efficiently.

💼 Career

Error logging is a key skill for DevOps engineers to maintain reliable automation scripts and troubleshoot failures.

1

Create the error log dictionary

Create a dictionary called $ErrorLog initialized as an empty hashtable to store error messages and their counts.

PowerShell

# Your code here

Need a hint?

Use @{} to create an empty hashtable in PowerShell.

2

Define commands to run

Create a variable called $Commands and assign it an array with these exact strings: 'Get-Process', 'Get-Service', and 'Get-NonExistentCommand'.

PowerShell

$ErrorLog = @{}
# Your code here

Need a hint?

Use @( ... ) to create an array in PowerShell.

3

Run commands and log errors

Use a foreach loop with variable $cmd to iterate over $Commands. Inside the loop, run Invoke-Expression $cmd inside a try block. Catch errors in a catch block. In the catch block, get the error message from $_.Exception.Message. If the message is already a key in $ErrorLog, increment its value by 1; otherwise, add it with value 1.

PowerShell

$ErrorLog = @{}
$Commands = @('Get-Process', 'Get-Service', 'Get-NonExistentCommand')
# Your code here

Need a hint?

Use try { ... } catch { ... } to handle errors in PowerShell.

Use Invoke-Expression to run the command string.

4

Print the error summary

Use a foreach loop with variables $message and $count to iterate over $ErrorLog.GetEnumerator(). Inside the loop, print the error message and count in the format: Error: {message} - Count: {count} using Write-Output.

PowerShell

$ErrorLog = @{}
$Commands = @('Get-Process', 'Get-Service', 'Get-NonExistentCommand')
foreach ($cmd in $Commands) {
    try {
        Invoke-Expression $cmd
    } catch {
        $msg = $_.Exception.Message
        if ($ErrorLog.ContainsKey($msg)) {
            $ErrorLog[$msg] += 1
        } else {
            $ErrorLog[$msg] = 1
        }
    }
}
# Your code here

Need a hint?

Use $ErrorLog.GetEnumerator() to loop over hashtable keys and values.

Use Write-Output to print lines.