This definitely won't win any beauty awards, but at least returns the same result: ([System.Security.Cryptography.HashAlgorithm]::Create('MD5').ComputeHash([System.Text.Encoding]::UTF8.GetBytes((gc C:\a-directory\*.*) -join '')) | % { $_.ToString('x2') }) -join ''
bash -c "cat directory | md5sum"([System.Security.Cryptography.HashAlgorithm]::Create('MD5').ComputeHash([System.Text.Encoding]::UTF8.GetBytes((gc C:\a-directory\*.*) -join '')) | % { $_.ToString('x2') }) -join ''