APPEND  File  String

This command attaches the specified String to the end of 
the File.

File     - A File name
String   - Any character, sentence, or whatever.

Example :

  .MyVar = "This is a "   <-- Note the space
  Append Env:.MyVar "Test"

Now .MyVar should contain "This is a Test"
You can use this command to append a String to any file.