PowerShell example to edit multiple files. This specific example remove the first 15 chars from every XML file in a directory.
get-childitem D:TEMPMessages *.xml |
% {
[string]$sFileContent = cat $_.fullname
$sFileContent = $sFileContent.substring(15,$sFileContent.length-15) | Out-File -Filepath $_.fullname
echo $_.fullname
}