The interface between user and Linux: Shell command
From;    Author:Stand originally
Shell is the interface between user and Linux operating system. There are a variety of Shell in Linux, among them what default uses is Bash. This chapter is told about

the working principle of Shell, the sort of Shell, the general operation of Shell reachs the character of Bash.

What is Shell

The Shell of Linux system serves as the crust of the operating system, offer the port of use operating system for the user. It is explanation of command language, command

Program and programming a general designation of the language.

Shell is the interface program between user and Linux kernel, if imagine Linux kernel into the center of a sphere, shell is around

Of the kernel outer. When handing an order to Linux from Shell or other program, the kernel is met make corresponding response.

Shell is interpreter of language of a command, it has its built-in Shell to command market, shell also can by place of other application process is moved in the system

With. The command that the user inputs below clew accord with is explained first by Shell pass Linux core next.

Have a few orders, for instance change job catalog commands Cd, it is to include in Shell interior. Still have a few orders, copy a command for example Cp and move

Move command Rm, it is the separate order below a certain catalog in system of consist in file. To the user character, need not caring a command is to build in Shell

Interior still is a separate order.

Whether is Shell checks an order above all internal order, whether is except reexamination an application process (the applied process here can be

The utility program of Linux itself, be like Ls and Rm, also can be bought commercial program, be like Xv, free perhaps software, be like Emacs) . Next

Shell searchs these to use a program in search method (the catalog list) that search method can find executable program namely. If key in command

Either an interior commands and did not find this executable document in method, will display a wrong message. If can find a lot successfully

Your, this interior commands or applied process will be decomposed to be a system to call and pass Linux kernel.

Another of Shell main character is its oneself explains namely model programming language, the language supports Shell programming great majority

In the program element that the visibility in advanced language goes to, be like function, variable, array and programme controll structure. Shell programming language learns easily simply, allow where to

The command that hints Fu Zhongneng is keyed in can be put in an executable Shell program.

Login successfully when average user, the system will execute an order that calls Shell. Just about Shell process offerred magic figures drawn by Taoist priests to invoke or expel spirits and bring good or ill fortune of command travel clew. As

Acquiescent value (the Shell with TurboLinux acquiescent system is BASH) , use to average user " $ " make clew magic figures drawn by Taoist priests to invoke or expel spirits and bring good or ill fortune, to super user (Root) is used " # " make
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