GetFileEncoding.ps1

function Get-FileEncoding {
    [CmdletBinding()]
    param (
        [ValidateScript({Test-Path -Path $_})]
        [string]$Path
    )
    
    $fullpath = (Resolve-Path -Path $Path).Path
   
    $file = [System.IO.FileStream]::new($fullpath,[System.IO.FileMode]::Open)
    $bytes = [byte[]]::new(100)
    $null = $file.Read($bytes,0,$bytes.Length)
    $file.Close()
    $file.Dispose()

    $chars = [char[]]::new($bytes.Length)

    for ($i = 0; $i -lt $bytes.length; $i++){ 
        $chars[$i] = [char]$bytes[$i]    
    }

    <#
            Signatures and descripions from here:
            https://en.wikipedia.org/wiki/List_of_file_signatures
            https://www.garykessler.net/library/file_sigs.html
    #>
    $encoding = @{
        'FF-FE'             = 'Byte-order mark for text file encoded in little-endian 16-bit Unicode Transfer Format'
        'FE-FF'             = 'Byte-order mark for 16-bit Unicode Transformation Format/2-octet Universal Character Set (UTF-16/UCS-2), big-endian files.'
        'FF-FE-00-00'       = 'Byte-order mark for text file encoded in little-endian 32-bit Unicode Transfer Format'
        '00-00-FE-FF'       = 'Byte-order mark for 32-bit Unicode Transformation Format/4-octet Universal Character Set (UTF-32/UCS-4), big-endian files.'
        'EF-BB-BF'          = 'UTF-8 encoded Unicode byte order mark. (PowerShell friendly)'
        '7B-5C-72-74-66-31' = 'Rich Text Format'
    }

    $hex = [System.BitConverter]::ToString($bytes)
    
    Microsoft.PowerShell.Utility\Write-Verbose "First $($bytes.Length) bytes in hex: $hex"
    
    foreach ($signature in $encoding.Keys) {
        if ($hex.StartsWith($signature)) {
            Microsoft.PowerShell.Utility\Write-Output "Found match: $signature, $($encoding.$signature) ($signature)" 
        }
    }
}