Text update writing

Here's a straightforward way:

t1 = OpenFile("text1.txt")
t2 = OpenFile("text2.txt")
t3 = WriteFile("text3.txt")

If t1 And t2 And t3 Then
	While Not Eof(t1) : WriteLine(t3, ReadLine$(t1)) : Wend
	While Not Eof(t2) : WriteLine(t3, ReadLine$(t2)) : Wend
EndIf

Or, you can also use ExecFile with cmd.exe or command.com, to use the DOS Copy command, like this

copy text1.txt+text2.txt text3.txt