How to join two text files, removing duplicates, in Windows

Question

file 1

A
B
C

file 2

B
C
D

file1 + file2 =

A
B
C
D

Is it possible to do using cmd.exe?

Answer 1

If you can affort to use a case insensitive comparison, and if you know that none of the lines are longer than 511 bytes (127 for XP), then you can use the following:

@echo off
copy file1.txt merge.txt >nul
findstr /lvxig:file1.txt file2.txt >>merge.txt
type merge.txt

For an explanation of the restrictions, see What are the undocumented features and limitations of the Windows FINDSTR command?.