Hour 1: Shell Basics

Hour 1: Shell basics-general Linux technology-Linux programming and kernel information. The following is a detailed description. 1. Command)
The command specifies a program that can be run in Unix. Commands include simple commands, complex commands, and compound commands. Complex commands can contain parameters and options. Compound commands are a combination of multiple commands separated.

2. Shell
Shell is a special program that provides interfaces between users and the system. It collects user input and executes the program according to user input. Therefore, in Unix, shell is also known as an interpreter.

3. Various types of Shell
In the Unix world, there are two main types of Shell:
Bourne Shell (including sh, ksh, and bash)
C Shell (including csh and tcsh)

4. The original Bourne Shell
In the middle of 70 years, Stephen Bourne, who worked at the AT&T Bell lab in New Jersey, completed the process. The Bournce Shell is the first Shell that appears on a Unix system. Usually installed in/bin/sh. It is also a powerful scripting language, with syntax similar to ALGOL programming language. The Bourne Shell provides process control, variables, regular expressions, process control, and powerful input/output and function features. The disadvantage is that the file name cannot be automatically filled up, and command history and command editing are not supported. It is difficult to execute multiple background processes and tasks.

5. C Shell
In the early 1980 s, Bill Joy developed C Shell, which was still at UC Berkeley. C Shell makes it easier for users to exchange with Shell. Another change is the programming style and C language. It supports command history, command alias, file name completion, and task control. It is short of weak input and output, lack of Function Support and fuzzy syntax.

6. Korn Shell
At the AT&T Bell lab, David Korn developed the Korn Shell, which incorporates the advantages of the C Shell into the Bourne Shell. It includes command history and historical replacement, command alias and Function Support, file name completion, and array to the Bourne shell.

7. Bourne Again Shell
It is part of the GNU program and used to replace sh in the GNU system. Bash, written by Brian Fox of the Free Software Foundation, is now maintained by Chester Ramey.

Bash implements ieee posix 1003.2/ISO 9945.2 Shell and Tool specifications. Strong portability. In addition to the advantages of the Korn Shell, it also supports:

Variable name, user name, machine name, command and file name are automatically filled
Spelling of path names in the cd command
Array with no size limit
It is calculated based on integers ranging from 2 to 64.