We can call the operating system kernel the software that is at the center of the operating system and has full control of the system. Kernel is the part of the operating system code that is always in memory, and it manages the operation of our system's units such as memory, CPU and software.

The GNU we mentioned above widely uses the Linux kernel as its kernel. Therefore, it creates an operating system with the GNU tools - software - on the Linux kernel, and for this reason, it would be much more accurate to specify it as GNU/Linux when naming it.

We will not cover the details of kernel and kernel types in this documentation, but you can access detailed information from the Internet.
For shell -shell-, we can say that it is the program that transmits the inputs it receives from the user to the operating system. We can divide shells into command line interface (CLI) or graphical user interface (GUI).
In this tutorial, we will implement applications on the "bash" shell.

Commonly used terminal in "Bash", "GNU/Linux" systems. It was written as a ‑terminal- replacement for the “sh” command interpreter used on UNIX systems by Steve Bourne, and hence named BASH -Bourne Again SHell- after the author of “sh”.
You can learn the shell you are using with the following commands.
echo $ 0
echo $ SHELL
Output:
/ bin / bash
Commonly used Unix and GNU/Linux command interpreters:
- Sh, – Bourne shell
- Bash, – Bourne Again shell
- ksh, – Korn shell
- Tcsh/Csh
- zsh
- Fish

Research topics: UNIX, BSD
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