Shell: Why is it shell?

Shell's first question: why is it shell-general Linux technology-Linux programming and kernel information? The following is a detailed description. We know that computer operations cannot leave hardware, but users cannot directly drive hardware. hardware drivers can only be controlled through a software called "Operating System, in fact, the linux we talk about every day is simply an operating system, which we call "core )". However, from the user's point of view, the user cannot directly operate the kernel, but communicates with the kernel through the "shell" program of the kernel, that is, the so-called shell. This is exactly the naming relationship between the image of the kernel and the shell.

From a technical point of view, shell is an interface between the user and the system. It allows the user to use the system through command line to complete the work. Therefore, the simplest definition of shell is --- Command Interpreter ):

Translate users' commands to the core processing, and translate the core processing results to the user.

Every time we log in, we get an interactive shell called login shell or primary shell. From the perspective of process, the commands we run in shell are all subitineraries produced by shell. This is now called fork. For shell scripts, the commands in the script are executed by another non-interactive subshell. That is, the primary shell generates the sub shell itinerary, and the sub shell then generates the itinerary of all commands in the script. (For the itinerary, we will have the opportunity to add it later .)

Here, we must know that the kernel and shell are two different sets of software, and they can all be replaced:

Different operating systems use different kernel, and different shells can be used on the same kernel. In a linux preset system, you can usually find several different shells, which are usually listed in the following files:/etc/shells

Different shells have different functions and are also different from each other, or say "The Same Thing ". Common shells are mainly divided into two major types:

Sh:
Burne shell (sh)
Burne again shell (bash)

Csh:
C shell (csh)
Tc shell (tcsh)
Korn shell (ksh)
(FIXME)

The default shell of most Linux systems is bash. The reasons are as follows: Free Software and powerful functions.

Bash is one of the most successful products of the gnu project. It has been favored by many Unix users since its launch and has gradually become a system standard of many organizations.