How to get an MD5 checksum in PowerShell
Starting in PowerShell version 4, this is easy to do for files out of the box with the Get-FileHash
cmdlet:
Get-FileHash <filepath> -Algorithm MD5
This is certainly preferable since it avoids the problems the solution for older PowerShell offers as identified in the comments (uses a stream, closes it, and supports large files).
If the content is a string:
$someString = "Hello, World!"
$md5 = New-Object -TypeName System.Security.Cryptography.MD5CryptoServiceProvider
$utf8 = New-Object -TypeName System.Text.UTF8Encoding
$hash = [System.BitConverter]::ToString($md5.ComputeHash($utf8.GetBytes($someString)))
For older PowerShell version
If the content is a file:
$someFilePath = "C:\foo.txt"
$md5 = New-Object -TypeName System.Security.Cryptography.MD5CryptoServiceProvider
$hash = [System.BitConverter]::ToString($md5.ComputeHash([System.IO.File]::ReadAllBytes($someFilePath)))
Here's a function I use that handles relative and absolute paths:
function md5hash($path)
{
$fullPath = Resolve-Path $path
$md5 = new-object -TypeName System.Security.Cryptography.MD5CryptoServiceProvider
$file = [System.IO.File]::Open($fullPath,[System.IO.Filemode]::Open, [System.IO.FileAccess]::Read)
try {
[System.BitConverter]::ToString($md5.ComputeHash($file))
} finally {
$file.Dispose()
}
}
Thanks to @davor above for the suggestion to use Open() instead of ReadAllBytes() and to @jpmc26 for the suggestion to use a finally block.
If you are using the PowerShell Community Extensions there is a Get-Hash commandlet that will do this easily:
C:\PS> "hello world" | Get-Hash -Algorithm MD5
Algorithm: MD5
Path :
HashString : E42B054623B3799CB71F0883900F2764