How to Merge Multiple Videos on Ubuntu – Command-Line Video Tools

I want to merge videos in batch size of twenty (20) each. I'm running a Linux machine. The videos are in mp4 format and moderate quality. Some even have the audio stream missing. So far I've tried ffmpeg, mencoder, cvlc/vlc and MP4Box. I want to write a command line script to achieve this, since I'm doing batch processing.

The main issue is that some of the solutions I tried work well for two videos, some work well for videos with audio stream and yet others work well for some other subset of my video set. However, I have not been able to find a comprehensive solution for this task.