PowerShell

Convert a File's Character Encoding from UTF-8 to UFT-8-BOM

See more HTML-to-XML/Text Examples

To add a utf-8 BOM to a file is just a matter of prepending these 3 bytes to the file: 0xEF 0xBB 0xBF.

This may be difficult in some programming languages, or it may be trivial in either. Therefore, the Chilkat solution you see here might be helpful, or in a language such as C++, the Chilkat solution isn't really necessary because it's easy to do yourself.

PowerShell

Add-Type -Path "C:\chilkat\ChilkatDotNet47-x64\ChilkatDotNet47.dll"

$success = $false

# This example assumes the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

$charset = New-Object Chilkat.Charset

$charset.FromCharset = "utf-8"
$charset.ToCharset = "bom-utf-8"

$success = $charset.ConvertFile("qa_data/txt/helloWorld.txt","qa_output/helloWorldBom.txt")
if ($success -ne $true) {
    $($charset.LastErrorText)
    exit
}

$("Success.")