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# Calculating checksums of multiple files in PowerShell

Sat
27
Jan 2024

Today I would like to share with you a small script that I developed some time ago and I use regularly since then. It calculates hashes (checksums) for multiple files and saves them to a text file. It is written in PowerShell.

A bit of background: While working with games, I often need to move large amounts of data. Packages of 150 GB or more are not uncommon. When copying, uploading, downloading them, how to make sure not a single bit has changed? A solution is obviously to calculate some checksum and compare it between the source and the destination location. If the checksums don't match, it would be beneficial to avoid transferring the entire package again. Thus, packing it into multiple files (a multi-part .7z archive) is a good idea. This, however, requires a convenient way to calculate checksums of multiple files at once.

The script

My script is actually just a single line:

$ExtractName = @{l='Name';e={Split-Path $_.Path -Leaf}}; Get-FileHash -Path INPUT_MASK | Select-Object -Property Hash, $ExtractName > OUTPUT_FILE

To use it:

1. Open PowerShell console.
2. Go to the directory with your archives to hash.
3. Paste the command provided above. Before pressing ENTER:
   1. Replace "INPUT_MASK" with the mask of your files to hash. For example, if the archive files are named "Archive.7z.001", "Archive.7z.002", etc., you can type in "Archive.7z.*".
   2. Replace "OUTPUT_FILE" with the name or path of the output file to be created.
4. Hit ENTER.

Example PowerShell session:

PS C:\Users\Adam Sawicki> cd E:\tmp\checksum_test\
PS E:\tmp\checksum_test> $ExtractName = @{l='Name';e={Split-Path $_.Path -Leaf}}; Get-FileHash -Path Archive.7z.* | Select-Object -Property Hash, $ExtractName > Checksums.txt
PS E:\tmp\checksum_test>

If input files are large, it may take few minutes to execute. After it is complete, the output file "Checksums.txt" may look like this:

Hash                                                             Name          
----                                                             ----          
CBBABFB5529ACFB6AD67502F37444B9273A9B5BB7AF70EFA0FF1F1EC99B70895 Archive.7z.001
185D73ECBCECB9302981C97D0DDFC4B96198103436F23DB593EA9BAFBF997DAC Archive.7z.002
086640842CC34114B898D2E19270DCE427AC89D64BCD9E8E3D8D955D69588402 Archive.7z.003
BE536C66854530236DA924B1CAED44D0880D28AAA66420F6EBE5F363435BEB4F Archive.7z.004

You can then execute the same script on the destination machine of your transfer and compare files and checksums to make sure they match.

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