regex are:

$text =~ s/&(?!amp|quot|apos|lt|gt)/!38/g;
$text =~ s/"(?!amp|quot|apos|lt|gt)/!34/g;
$text =~ s/<(?!amp|quot|apos|lt|gt)/!40/g;
$text =~ s/>(?!amp|quot|apos|lt|gt)/!41/g;
$text =~ s/'(?!amp|quot|apos|lt|gt)/!39/g;


##</code><code>##

!40?xml version=!341.0!34 encoding=!34UTF-8!34?!41
!40TRANSACTION!41
    !40FIELDS!41
        !40FIELD KEY=!34user!34!41name!40/FIELD!41
        !40FIELD KEY=!34password!34!41pass!38word!40/FIELD!41
        !40FIELD KEY=!34operation_type!34!41!40do_what!41!40/FIELD!41
     !40/FIELDS!41
!40/TRANSACTION!41