BOM detector

is-bom-file.ps1

function Is-BOM-File ($filename) {
  $bytes = Get-Content -Encoding byte -TotalCount 4 $filename
  $encoding = [Text.Encoding]::GetEncodings() `
    | ForEach { $_.GetEncoding() } `
    | Where-Object { -not $_.IsSingleByte } `
    | Where-Object {
      $preamble = $_.GetPreamble()
      For ($i = 0; $i -lt $preamble.Length; $i++) {
        if ($bytes[$i] -ne $preamble[$i]) {
          return $false
        }

        $true
      }
    }

  $encoding -ne $null
 }