Powershell function to get file hash

get-hash.ps1

<#
.SYNOPSIS
    Gets the hash value of a file or string
    
.DESCRIPTION
    Gets the hash value of a file or string
    It uses System.Security.Cryptography.HashAlgorithm (http://msdn.microsoft.com/en-us/library/system.security.cryptography.hashalgorithm.aspx)
    and FileStream Class (http://msdn.microsoft.com/en-us/library/system.io.filestream.aspx)
    Based on: http://blog.brianhartsock.com/2008/12/13/using-powershell-for-md5-checksums/ and some ideas on Microsoft Online Help
    
    Be aware, to avoid confusions, that if you use the pipeline, the behaviour is the same as using -Text, not -File
.PARAMETER File
    File to get the hash from.
    
.PARAMETER Text
    Text string to get the hash from
    
.PARAMETER Algorithm
    Type of hash algorithm to use. Default is SHA1
    
.EXAMPLE
    C:\PS> Get-Hash "hello_world.txt"
    Gets the SHA1 from myFile.txt file. When there's no explicit parameter, it uses -File
.EXAMPLE    
    Get-Hash -File "C:\temp\hello_world.txt"
    Gets the SHA1 from myFile.txt file
    
.EXAMPLE
    C:\PS> Get-Hash -Algorithm "MD5" -Text "Hello Wold!" 
    Gets the MD5 from a string
       
.EXAMPLE
    C:\PS> "Hello Wold!" | Get-Hash
    We can pass a string throught the pipeline  
    
.EXAMPLE
    Get-Content "c:\temp\hello_world.txt" | Get-Hash
    It gets the string from Get-Content
.EXAMPLE
    Get-ChildItem "C:\temp\*.txt" | %{ Write-Output "File: $($_)   has this hash: $(Get-Hash $_)" }
    This is a more complex example gets the hash of all "*.tmp" files
    
.NOTES
    DBA daily stuff (http://dbadailystuff.com) by Josep Mart�nez Vil�
    Licensed under a Creative Commons Attribution 3.0 Unported License
    
.LINK
    Original post: http://dbadailystuff.com/2013/03/11/get-hash-a-powershell-hash-function/
#>
function Get-Hash
{
    Param
    (
        [parameter(Mandatory=$true, ValueFromPipeline=$true, ParameterSetName="set1")]
        [String]
        $text,
        [parameter(Position=0, Mandatory=$true, ValueFromPipeline=$false, ParameterSetName="set2")]
        [String]
        $file = "",
        [parameter(Mandatory=$false, ValueFromPipeline=$false)]
        [ValidateSet("MD5", "SHA", "SHA1", "SHA-256", "SHA-384", "SHA-512")]
        [String]
        $algorithm = "SHA1"
    )

    Begin
    {
        $hashAlgorithm = [System.Security.Cryptography.HashAlgorithm]::Create($algorithm)
    }
	Process
	{
        $md5StringBuilder = New-Object System.Text.StringBuilder 50
        $ue = New-Object System.Text.UTF8Encoding 

        if ($file){
            try {
                if (!(Test-Path -literalpath $file)){
                    throw "Test-Path returned false."
                }
            }
            catch {
                throw "Get-Hash - File not found or without permisions: [$file]. $_"
            } 

            try {        
                [System.IO.FileStream]$fileStream = [System.IO.File]::Open($file, [System.IO.FileMode]::Open);
                $hashAlgorithm.ComputeHash($fileStream) | % { [void] $md5StringBuilder.Append($_.ToString("x2")) }
            }
            catch {
                throw "Get-Hash - Error reading or hashing the file: [$file]"
            } 
            finally {
                $fileStream.Close()
                $fileStream.Dispose()
            }
        }
        else {
            $hashAlgorithm.ComputeHash($ue.GetBytes($text)) | % { [void] $md5StringBuilder.Append($_.ToString("x2")) }
        }
        
        return $md5StringBuilder.ToString()
    }
}