Unix philosophy
Do one thing and do it well - Write programs that do one thing and do it well. Write programs to work together. Write programs to handle text streams, because that is a universal interface.
Everything is file - Ease of use and security is offered by treating hardware as a file.
Small is beautiful
Store data and configuration in flat text files - Text file is a universal interface. Easy to create, backup and move files to another system.
Use shell scripts to increase leverage and portability - Use shell script to automate common tasks across various UNIX / Linux installations.
Chain programs together to complete complex task - Use shell pipes and filters to chain small utilities that perform one task at time.
Choose portability over efficiency.
Keep it Simple, Stupid (KISS).