Easily Compare Two Folders by Using PowerShell

Summary: Microsoft Scripting Guy Ed Wilson illustrates how to compare two folders by using Windows PowerShell.

Microsoft Scripting Guy Ed Wilson here. It is an absolutely beautiful day in Charlotte, North Carolina. The early morning rain gave way to a colorful rainbow.

My manager bought me a new laptop, and I have been busy working on it; installing software, copying files, and migrating settings. The old laptop will be paved, so it is important to ensure I get everything copied to the new laptop.

Most of the major things are automatically transferred, but there are always a few folders that seem to get left behind. This is especially true because I am still working while doing the migration, and there is always a danger of missing something.

In the past, I might write a script to compare two folders to ensure they are identical. However, with Windows PowerShell, I do not need to write a script. I can type a simple command to compare two folders.

For example, I use a folder named fso that is located directly off of the root of the C: drive as my scratch directory. I leave all kinds of stuff in that directory, including files that contains important sample scripts and sample text files, spreadsheets, and databases. I use these files when writing articles, teaching, or making presentations. This folder is shown in the following figure.

There is nothing vital in the folder, but it is useful to have those files, so I want to ensure I have a good copy of the folder. Also, I am not capable of quickly reading through a folder with 144 files to ensure nothing is missing. To compare two folders I perform the following steps:

1. Use the Get-ChildItem cmdlet with the recurse switched parameter and the path parameter (points to the folder to use for reference) to obtain a collection of fileinfo objects. Store these objects in a variable.
2. Use the Get-ChildItem cmdlet with the recurse switched parameter and the path parameter (points to the folder to use for comparison) to obtain a collection of fileinfo objects. Store these objects in a different variable.
3. Use the Compare-Object cmdlet and specify the objects stored in the first variable to the ReferenceObject parameter. Supply the objects stored in the second variable to the DifferenceObject parameter.

Note   Do not get hung up on whether the first folder should be the reference object or the difference object. The position of the folder in the two parameters determines the direction of the comparison arrows, but as long as you know which folder is difference or reference, you will be fine.

The code I type on my laptop is shown here:

$fso = Get-ChildItem -Recurse -path C:\fso

$fsoBU = Get-ChildItem -Recurse -path C:\fso_BackUp

Compare-Object -ReferenceObject $fso -DifferenceObject $fsoBU

The code and associated output are shown in the following figure. The output tells me that inputobject (this is the difference object parameter) is missing three files: a.txt, b.txt, and c.txt. I need to copy these three files to the c:\fso_backup folder.

Well, it is the weekend, and as you can see, it is a beautiful day. I am going to get back to work on my laptop. Hope you have an awesome weekend. See you tomorrow.

I invite you to follow me on Twitter and Facebook. If you have any questions, send email to me at scripter@microsoft.com, or post your questions on the Official Scripting Guys Forum. See you tomorrow. Until then, peace.

Ed Wilson, Microsoft Scripting Guy