Using Powershell to calculate/compare MD5 hashes

This entry is part 1 of 4 in the series MD 5 Calculation

Here’s some code to a) calculate a MD5 hash for a given file and b) to compare the hash with a MD5 provided in an external file. The scripts expects the MD5 file to have the same name, but MD5 extension. Credit goes to the friendly souls providing the original code, I just copied and pasted everything together.

The comparison is just visual, both MD5 hashes — the calculated and the provided one — are printed on the screen, it’s easily to extend it for an automated comparison.

# Reference:
### Step A: Get the name of the file
Function Get-FileName($initialDirectory)
 [System.Reflection.Assembly]::LoadWithPartialName("") |
$OpenFileDialog = New-Object System.Windows.Forms.OpenFileDialog
$OpenFileDialog.initialDirectory = $initialDirectory
$OpenFileDialog.filter = "All files (*.*)| *.*"
$OpenFileDialog.ShowDialog() | Out-Null
} #end function Get-FileName
# *** Entry Point to Script ***
$file =  Get-FileName -initialDirectory "H:\MD5"
### Step B: Create a file handle from this string and calculate the MD5 sum
$filehandle = Get-ChildItem $file
# write-host "file: " $file
# write-host "DirectoryName: " $filehandle.DirectoryName
write-host "Name: " $filehandle.Name
# write-host "pure Name: " $filehandle.BaseName
$md5 = New-Object -TypeName System.Security.Cryptography.MD5CryptoServiceProvider
$hash = [System.BitConverter]::ToString($md5.ComputeHash([System.IO.File]::ReadAllBytes($filehandle))).ToLower().Replace("-","")
write-host "Calculated Hashsum: "  $hash
### Step C: Get the MD5 sum from the MD5 sum file matching the other filename
$md5handle =  Get-ChildItem $($filehandle.DirectoryName + "\" + $filehandle.BaseName + ".md5")
$md5sum = [IO.File]::ReadAllText($md5handle)
write-host "Provided MD5        " $md5sum


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