Shell is a term, which is often used and often misunderstood. Like the shell of an egg, either hen or Python snake, or a mussel, the shell in computer science is generally seen as a piece of software that provides an interface for a user to some other software or the operating system. So the shell can be an interface between the operating system and the services of the kernel of this operating system. But a web browser or a program functioning as an email client can be seen as shell as well.
Understanding this, it's obvious that a shell can be either
- a command-line interface (CLI) or
- a graphical user interface (GUI)
But in most cases the term shell is used as a synonym for a command line interface (CLI). The best known and most often used shells under Linux and Unix are the Bourne-Shell, C-Shell or Bash shell. The Bourne shell (sh) was modelled after the Multics shell, and is the first Unix shell. Most operating system shells can be used in both interactive and batch mode.
System programming and Python
System programming (also known as systems programming) stands for the activity of programming system components or system software. System programming provides software or services to the computer hardware, while application programming produces software which provides tools or services for the user.
"System focused programming" serves as an abstraction layer between the application, i.e. the Python script or program, and the operating system, e.g. Linux or Microsoft Windows. By means of such an abstraction layer it is possible to implement platform independent applications in Python, even if they access operating specific functionalities. Python provides various modules to interact with the operating system, such as
- os
- platform
- subprocess
- shutils
- glob
- sys
Therefore Python is well suited for system programming, or even platform independent system programming. This is one of the reasons by the way why Python is wrongly considered by many as a scripting language. The proper way to say it: Python is a full-fledged programming language which can be easily used as a scripting language. The general advantages of Python are valid in system focused programming as well:
- simple and clear
- wel structured
- highly flexible
