Exploring Compare-Object in PowerShell

Welcome back to Wahman’s PowerShell Blog! Today we will explore a very useful cmdlet in PowerShell: Compare-Object. Whether you’re comparing text files, folder contents, or collections of objects, Compare-Object can be your best friend.

According to Microsoft:

Compare-Object
Compares two sets of objects.

What does Compare-Object do?

Compare-Object takes two collections (think arrays, lists, or output from other cmdlets) and identifies differences between them. The result will indicate which side (Set 1 or Set 2) the difference originated from using => or <= symbols.

Example 1: Comparing Two Simple Arrays (Beginner)

$array1 = @("apple", "banana", "cherry")
$array2 = @("banana", "cherry", "date")

Compare-Object -ReferenceObject $array1 -DifferenceObject $array2

Output:

InputObject SideIndicator
----------- -------------
apple       =<
date        =>

This tells us that apple exists only in the first array, and date only in the second.

Example 2: Check for File Differences (Intermediate)

$file1 = Get-Content -Path "C:\temp\original.txt"
$file2 = Get-Content -Path "C:\temp\modified.txt"

Compare-Object -ReferenceObject $file1 -DifferenceObject $file2

This is helpful for line-by-line comparisons of text files.

Example 3: Compare Hashtable Keys (Advanced)

$hash1 = @{ Name = "Alice"; Age = 30; City = "Stockholm" }
$hash2 = @{ Name = "Alice"; Age = 30; Country = "Sweden" }

$keys1 = $hash1.Keys
$keys2 = $hash2.Keys

Compare-Object -ReferenceObject $keys1 -DifferenceObject $keys2

This will show that City is present in the first hashtable, while Country is present in the second one.

Example 4: Compare Folder Contents Recursively (Advanced)

$folder1 = Get-ChildItem -Path "C:\FolderA" -Recurse | Select-Object -ExpandProperty FullName
$folder2 = Get-ChildItem -Path "C:\FolderB" -Recurse | Select-Object -ExpandProperty FullName

Compare-Object -ReferenceObject $folder1 -DifferenceObject $folder2

This is useful when validating folder syncs or backup consistency.

Summary

Compare-Object is a powerful tool in your PowerShell toolbox. From string arrays to folder trees, this cmdlet offers flexibility for a wide variety of comparison tasks. It’s straightforward for beginners and still highly useful in advanced scripts.

Happy scripting, and I will see you in the next post!