I need to merge two files using cmd argument. So can somebody tell me what is the command for that?

1) Copy file1.ext+file2.ext target.ext General purpose, text and things

2) Copy/a file1.ext+file2.ext target.ext DOS Text files copies to CTRL-Z, an end of file mark used by DOS. Kinda obsolete.

3) Copy/b file1.ext+file2.ext target.ext Merges binaries, ignores CTRL-Z's

Explanation:
file1 file2 files you want to merge. You can do more than 2 at once IE:
copy/b file1.ext+file2.ext+file3.ext+file4.ext .... but there is limit to how big a command line can get.

target.ext the name of the file you want the files merged into

You can also use the complete paths on the files. (copy/b c:\dos\file1.ext+c:\dos\file2.ext ... )