Often DVDs come with two notable directories: AUDIO_TS and VIDEO_TS. Usually VIDEO_TS is used for watching the video files contained in that DVD. These videos are formatted in VOB files, in almost all cases. Sometimes it’s better to convert these VOB files into a more usual video format, like mp4, avi, etc. You have to merge the VOB files into a single VOB file in the first step. And you can combine the VOB files into one using the Unix tool cat. cat is a simple and yet powerful tool for catenation of multiple files into one.
Open terminal in the VIDEO_TS directory (of course you can open terminal in another directory and still specify the input files path in the command; Unix is that flexible!) and execute the following command in it:
cat *.VOB > ./give_any_name.VOB
This would combine all VOB files into a single VOB file in that directory. Of course, you can specify another directory for output file, and give any name to the output file.
Here, * (asterisk) character acts as a wild card denoting all the files ending with VOB. And ./ denotes the present working directory.