Quite often these days when we download any movie files, they are split files with extensions like avi.001, avi.002 so on. In windows there is a very famous free tool called HJ Split to join the files.
In Ubuntu there is one such tool called lxSplit which can be used to join the files. Download the file from here. And install it or you can also get it from Package manager. After installation, files can be joined or split by following commands:
To Join files.
lxsplit -j smallfiles.bin.001
To split files.
lxsplit -s hugefile.bin 15M