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This article mainly introduces the example analysis of Shell programming, the article is very detailed, has a certain reference value, interested friends must read it!

Terminology

At the same time, it is also a programming language. As a command language, it interactively interprets and executes commands entered by users or automatically interprets and executes a series of predetermined commands; as a programming language, it defines a variety of variables and parameters. it also provides many control structures that are unique to high-level languages, including loops and branches.

In the sorting algorithm, Shell is the name of Hill sort.

Basically, there are two main categories of shell:

One: graphical interface shell (Graphical User Interface shell is GUI shell)

For example: the most widely used Windows Explorer (Microsoft's windows operating system), and also includes the well-known Linux shell, in which linux shell includes X window manager (BlackBox and FluxBox), as well as more powerful CDE, GNOME, KDE, XFCE.

Two: command-line shell (Command Line Interface shell, that is, CLI shell)

For example:

Bash / sh / ksh / csh (Unix/linux system)

(MS-DOS system)

Cmd.exe/ Command prompt characters (Windows NT system)

Windows PowerShell (Windows NT system that supports .NET Framework technology)

In the traditional sense, shell refers to the command-line shell, and if it is not specifically specified in the future, shell refers to the command-line shell.

The main interface between the text operating system and the outside is called shell. Shell is the outermost layer of the operating system. Shell manages your interaction with the operating system: waiting for your input, explaining your input to the operating system, and processing the output of various operating systems.

Shell provides a way for you to communicate with the operating system. This communication can be performed interactively (typed from the keyboard with an immediate response) or as shell script (non-interactive). Shell script is a string of shell and operating system commands placed in a file that can be reused. Essentially, shell script is a simple combination of command-line commands into a single file.

Shell is basically a command interpreter, similar to command under DOS. It receives user commands (such as ls, etc.) and then invokes the corresponding application. The more general shell has standard Bourne shell (sh) and C shell (csh).

Interactive shell and non-interactive shell

Interactive mode is where shell waits for your input and executes the commands you submit. This mode is called interactive because shell interacts with users. This mode is also familiar to most users: log in, execute some commands, and sign out. When you sign out, shell is terminated.

Shell can also run in another mode: non-interactive mode. In this mode, shell does not interact with you, but reads commands stored in the file and executes them. When it reads the end of the file, the shell terminates.

Type of shell

In UNIX, there are mainly:

Bourne shell (including sh,ksh,and bash)

Bourne shell (sh)

Korn shell (ksh)

Bourne Again shell (bash)

POSIX shell (sh)

C shell (including csh and tcsh)

C shell (csh)

TENEX/TOPS C shell (tcsh)

Bourne Shell

The first important standard, Unix Shell, was introduced in V7 Unix (AT&T 7th Edition) at the end of 1970, and was named after Stephen Bourne, the sponsor of the National Meteorological Network Computing Application Node (2004DKA50730) platform of the Ministry of Science and Technology. Bourne shell is an interchangeable command interpreter and command programming language. Bourne shell can be run as a login shell or a subshell of login shell (subshell). Only the login command can call Bourne shell as a login shell. At this point, shell first reads the / etc/profile file and the $HOME/.profile file. The / etc/profile file customizes the environment for all users, and the $HOME/.profile file customizes the environment for this user. Finally, shell will wait to read your input.

C Shell

Bill 喜悦 developed C shell at the University of California, Berkeley in the early 1980s. It is mainly to make it easier for users to use interactive functions, and to change the grammatical structure of ALGOL style into C language style. It adds command history, aliases, file name replacement, job control and other functions.

Korn Shell

For a long time, there were only two types of shell for people to choose from, Bourne shell for programming and C shell for interaction. In order to change this situation, David Korn, AT&T 's bell lab, developed Korn shell. Ksh combines all the interactive features of C shell and incorporates the syntax of Bourne shell. Therefore, Korn shell is widely welcomed by users. It also adds mathematical computing, process collaboration (coprocess), inline editing (inline editing) and other functions. Korn Shell is an interactive command interpreter and command programming language. It conforms to the international standard of POSIX-- one operating system. POSIX is not an operating system, but a standard aimed at application portability-across multiple platforms at the source program level.

Bourne Again Shell (bash)

Bash is part of the GNU program to replace Bourne shell. It is used in GNU-based systems such as Linux. Most Linux (Red Hat,Slackware,Caldera) use bash as the default shell, and when you run sh, you actually call bash.

POSIX Shell

POSIX shell is a variant of Korn shell. Currently, the biggest vendor offering POSIX shell is Hewlett-Packard. In HP-UX 11.0, POSIX shell is / bin/sh, and bsh is / usr/old/bin/sh.

The default shell for each major operating system:

Under AIX is Korn Shell.

The default for Solaris is Bourne shell.

C shell is the default for FreeBSD

The default for HP-UX is POSIX shell.

Linux is Bourne Again shell.

Windows PowerShell is a new interactive command line and task-based scripting technology, which enables information technology (IT) administrators to operate and control system management tasks automatically, thus improving the productivity of administrators. Windows PowerShell includes multiple system administration utilities, consistent syntax and naming conventions, and better navigation of general management data, such as enrollment, certificate stores, or Windows Management Instrumentation (WMI). Windows PowerShell also provides an intuitive scripting language specifically for IT management.

Shell is also a VB function, its function is to run the program, the syntax is Shell (command string [, window type])

Use

Shell is performed using the user's default credentials and environment.

In the UEFI environment, EFI's Shell environment provides a rich set of extended and enhanced commands. In future computers, the traditional DOS interface will be replaced by the SHELL environment, and all .exe files will not appear in future environments that support SHELL. Instead, the file suffix will be .efi. In the SHELL environment, * .efi files divided into IA32 and X64JI 32 bits cannot be run on X64 computers.

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