Test-Utf8BomHeaderPS.ps1

function Test-Utf8BomHeaderPS {
    [CmdletBinding(DefaultParameterSetName = "File")]
    [OutputType([bool])]
    param(
        [Parameter(Mandatory = $true, ValueFromPipeline = $true, ValueFromPipelineByPropertyName = $true, ParameterSetName = "File")]
        [System.IO.FileInfo]$File,

        [Parameter(Mandatory = $true, ValueFromPipeline = $true, ValueFromPipelineByPropertyName = $true, ParameterSetName = "Path")]
        [Alias("LiteralPath", "PSPath")]
        [string]$Path
    )

    process {
        if ($PSBoundParameters.ContainsKey("File")) {
            [System.IO.FileStream]$stream
            try {
                $stream = $File.OpenRead()
                $header = (1..3 | ForEach-Object {$stream.ReadByte().ToString("X2")}) -join ""
                Write-Output ($header -eq $bomHex)
            }
            finally {
                $stream.Dispose();
            }
        }
        else {
            [System.IO.FileStream]$stream
            try {
                $stream = [System.IO.FileStream]::New($Path, [System.IO.FileMode]::Open)
                $header = (1..3 | ForEach-Object {$stream.ReadByte().ToString("X2")}) -join ""
                Write-Output ($header -eq $bomHex)
            }
            finally {
                $stream.Dispose();
            }
        }
    }
}