Actually, you might not even need Perl for that one.

To "join" some files (appended one after another) try the following:
copy test1.txt +test2.txt +test3.txt test_appended.txt

More info copy /?

... To append files, specify a single file for destination, but multip
+le files
for source (using wildcards or file1+file2+file3 format).
[download]

Update: Utilitarian's way would work too - however it might be a tad slower... (unlikey to make any real difference though)