shell linux system between the user and the system kernel, corresponding to bridge between the system and the user, is responsible for parsing the input command and output binary code. Further, the shell also belong to a programming language, operating the machine to provide a user interactive interface, the user inputs the command to be transferred to the kernel and performs the processing result fed back.
1.shell type of development
In linux series system, its built-in types and a variety of different functions shell, while the built-in CentOS shell is not much supported CentOS can be found under the shell in / etc / shells file, as follows:
[root@system ~]# cat /etc/shells /bin/sh /bin/bash /sbin/nologin /usr/bin/sh /usr/bin/bash /usr/sbin/nologin /bin/tcsh /bin/ccsh
Overview of the role of 2.shell
After the system is started, the system shell was initialized before the user logs on, and some new sub-shell after the user login system, so long as the user login operation can be performed without the need to open the shell. Of course, a terminal window opening in a graphical interface, a child is actually open shell.
For computers, it can identify only the machine code of 0 and 1. However, when using a computer input is not machine code, but executed by letter or letters and numbers. These instructions are translated into machine code string of 0 and 1 in the composition after by shell, and transferred to the execution core, and to perform the output.
In fact, shell is a command language interpreter and collectively command programming language. Simply put, shell bridge between the Linux kernel layer and the user layer, to provide users with an interface using the operating system resources.
Each shell program under the Linux system is called a script by which you can call the system, public programs, tools, and compiled binaries bonded together and build applications.
3.shell works
shell in Linux is the kernel to communicate with the user interface to the system, is responsible for translating the user's commands to the system kernel into machine code execution and implementation of the results returned. shell command language interpreter is the most important system for Linux systems to provide users, but the shell does not belong to the core components of the system, but outside the kernel, and run as user mode. The entire user space, the shell user underlying layer, and in contact with the kernel space kernel. In fact, shell is a separate process system after the early start is user-initiated.