Hashing function for PowerShell

get-hash.ps1

param(
    [string]$pattern = "*.*",
    [ValidateSet("md5", "sha1", "sha256", "sha384", "sha512")]$algorithm = "sha1",
    [switch]$recurse
)

[Reflection.Assembly]::LoadWithPartialName("System.Security") | out-null

if ($algorithm -eq "sha1") {
    $hashimpl = new-Object System.Security.Cryptography.SHA1Managed
}
elseif ($algorithm -eq "sha256") {
    $hashimpl = new-Object System.Security.Cryptography.SHA256Managed
}
elseif ($algorithm -eq "sha384") {
    $hashimpl = new-Object System.Security.Cryptography.SHA384Managed
}
elseif ($algorithm -eq "sha512") {
    $hashimpl = new-Object System.Security.Cryptography.SHA512Managed
}
elseif ($algorithm -eq "md5") {
    $hashimpl = new-Object System.Security.Cryptography.MD5CryptoServiceProvider
}

$pattern | %{
    $files = get-childitem -Recurse:$recurse $_ | ?{ $_.PSIsContainer -eq $false }

    if ($files -ne $null) {
        $files | %{
            $filename = $_.FullName
            $hash = ""

            $file = [System.IO.File]::Open($filename, "open", "read")
            $hashimpl.ComputeHash($file) | %{
                $hash = $hash + $_.ToString("x2")
            }
            $file.Dispose()

            $result = new-object PSObject
            $result | add-member NoteProperty "Path" $filename
            $result | add-member NoteProperty "Hash" $hash
            write-output $result
        }
    }
}