Get-MD5.ps1

# Victor Vogelpoel
#
# Disclaimer
# This script is provided AS IS without warranty of any kind. I disclaim all implied warranties including, without limitation,
# any implied warranties of merchantability or of fitness for a particular purpose. The entire risk arising out of the use or
# performance of the sample scripts and documentation remains with you. In no event shall I be liable for any damages whatsoever
# (including, without limitation, damages for loss of business profits, business interruption, loss of business information,
# or other pecuniary loss) arising out of the use of or inability to use the script or documentation.

function Get-MD5
{
    [CmdletBinding(SupportsShouldProcess=$false)]
    param
    (
        [Parameter(Mandatory=$true, ValueFromPipeline=$true, ValueFromPipelineByPropertyName=$true, HelpMessage="file(s) to create hash for")]
        [Alias("File", "Path", "PSPath", "String")]
        [ValidateNotNull()]
        $InputObject
    )

    begin
    {
        $cryptoServiceProvider    = [System.Security.Cryptography.MD5CryptoServiceProvider]
        $hashAlgorithm             = new-object $cryptoServiceProvider
    }

    process
    {
        $hashByteArray = ""

        $item = Get-Item $InputObject -ErrorAction SilentlyContinue
        if ($item -is [System.IO.DirectoryInfo])    { throw "Cannot create hash for directory" }
        if ($item)                                     { $InputObject = $item }

        if ($InputObject -is [System.IO.FileInfo])
        {
            $stream         = $null;
            $hashByteArray    = $null

            try
            {
                $stream                 = $InputObject.OpenRead();
                $hashByteArray             = $hashAlgorithm.ComputeHash($stream);
            }
            finally
            {
                if ($stream -ne $null)
                {
                    $stream.Close();
                }
            }
        }
        else
        {
            $utf8             = new-object -TypeName "System.Text.UTF8Encoding"
            $hashByteArray     = $hashAlgorithm.ComputeHash($utf8.GetBytes($InputObject.ToString()));
        }

        Write-Output ([BitConverter]::ToString($hashByteArray)).Replace("-","")
    }
}