How to delete files in a directory, that exist in another directory?

Question 1

What I need is a ‘subtract’ operation on sets of files in different directories. Assuming this file system hierarchy:

A1.txt
A2.txt
A3.txt

B2.txt
B4.txt

… I’d like to remove all files under A that also exist under B (no recursion, and I only need to compare file names).

The result should be:

A1.txt
A3.txt

(nothing changed in B)

The target OS is Windows – either command line or a GUI tool. I’m also OK with a UNIX command-line approach – I have GnuWin32 installed.

Question 2

Create a list of files in B, replace B by A and remove them.

/bin/ls -1 B/ | xargs -I {} echo rm A/{}

remove the echo once you have it. For example:

$ ls A/
1 2 3
$ ls B/
1 2 
$ /bin/ls -1 B/ | xargs -I {} echo rm A/{}
rm A/1
rm A/2

If you have many files, I suggest doing something akin to

#!/bin/sh
for f in `ls -1 B/*`
do rm A/$f
done

Making sure that files with spaces and control character work is left as an exercise to the reader ^_-