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How to understand shell, in view of this problem, this article introduces the corresponding analysis and answers in detail, hoping to help more partners who want to solve this problem to find a more simple and feasible way.

Shell is the user interface of the system, which provides an interface for users to interact with the kernel. It receives the command entered by the user and sends it to the kernel for execution.

Shell is actually a command interpreter that interprets commands entered by the user and sends them to the kernel. Not only that, Shell has its own programming language for

In the editing of commands, it allows users to write programs made up of shell commands. The Shell programming language has many of the features of a common programming language, such as

Loop structure and branch control structure, Shell programs written in this programming language have the same effect as other application programs.

We can use SHELL to manage most of the Linux system, for example:

1. Document management

two。 User management

3. Authority management

4. Disk management

5. Software management

6. Network management

.

There are two ways to use Shell:

Inefficient input commands are suitable for a small amount of work

Shell Script is efficient and suitable for complex and repetitive tasks.

Summary of content:

Bash shell prompt

Shell syntax

Bash characteristics

Linux gets help

1. Bash shell prompt:

=

[root@tianyun ~] # echo $PS1

[\ u@\ h\ W]\ $

[root@tianyun ~] # date

Wednesday, 24 October 2019, 09:38:54 CST

[root@tianyun ~] # whoami

Root

[root@tianyun ~] # useradd jack

[root@tianyun ~] # passwd jack

Changing password for user jack.

New UNIX password:

BAD PASSWORD: it is WAY too short

Retype new UNIX password:

Passwd: all authentication tokens updated successfully.

II. Shell grammar

=

Command option parameter

[root@tianyun ~] # ls

[root@tianyun] # ls-a

[root@tianyun] # ls-a / home

Command: the body of the entire shell command

Options: will affect the behavior of fine-tuning commands / / usually with -,--

Parameters: the object on which the command acts

III. Basic characteristics of bash

1. Automatic completion

# ls / etc/sysconfig/network-scripts/

# ls / etc/sysconfig/network-scripts/ifcfg-eth0

# cat / etc/sysconfig/network-scripts/ifcfg-eth0

# systemctl restart crond.service

# date-s 12:30

two。 Shortcut key

^ C terminates the program running at the front desk / / ping 10.18.40.100

^ D exit equivalent exit

^ L clear screen

Move the ^ A cursor to the front / / edit command on the command line

Move the ^ E cursor to the back end of the command line / / Edit command

^ U Delete all characters before the cursor / / Edit command

^ K Delete all characters after cursor / / Edit command

^ R search history command, using keywords

Alt+. Refer to the last argument of the previous command, which is equivalent to! $

ESC. Refer to the last argument of the previous command, which is equivalent to! $

# ls / etc/sysconfig/network-scripts/ifcfg-eth0

# cat ESC.

3. Historical command

# history

a. Cursor up and down keys

B. ^ R / / search history command (enter a keyword for a command: must be continuous)

C.! 220 / execute order 220 of history order

! The most recent command in the string / / search history command that begins with the xxxx character, for example! ser

! $/ / refers to the last argument of the previous command

Example 1:

[root@instructor ~] # ls / root / home

[root@instructor ~] # cd! $

Cd / home

Example 2:

[root@instructor ~] # ls / root / home

[root@instructor ~] # touch! $/ file1

Touch / home/file1

Example 3:

[root@instructor ~] # systemctl restart crond

[root@instructor ~] # ls

[root@instructor ~] # date

[root@instructor ~] #! sy

In a week's time.

4. Command alias

[root@tianyun ~] # alias tianyun='cat / etc/sysconfig/network-scripts/ifcfg-eth0' / / establish an alias (temporary, valid only on the current Shell)

[root@tianyun ~] # unalias tianyun / / cancel the alias tianyun

[root@tianyun ~] # alias / / View the current alias of the system

Ll='ls-l-color=tty'

[root@tianyun ~] # ll

[root@tianyun ~] # / bin/ls

[root@tianyun] # / bin/ls-- color

[root@tianyun ~] # type-a ls / / View command type

Ls is aliased to `ls-- color=auto'

Ls is / usr/bin/ls

Ls is / bin/ls

[root@tianyun ~] # / bin/ls

[root@tianyun ~] # / usr/bin/ls

[root@tianyun ~] # ls / / Alias priority

[root@tianyun] #\ ls / / Skip aliases

[root@tianyun] # cp-rf / etc / tmp / / for the first time

[root@tianyun] # cp-rf / etc / tmp / / second time

[root@tianyun] #\ cp-rf / etc / tmp

[root@tianyun] # type-a cp

Cp is aliased to'cp-i'

Cp is / usr/bin/cp

Cp is / bin/cp

Permanent alias:

One of / etc/bashrc shell configuration files

[root@tianyun ~] # gedit / etc/bashrc / / add as below

Alias tianyun='cat / etc/sysconfig/network-scripts/ifcfg-eth0'

4. Linux gets help

1. Command-- help

# ls-help

Usage: ls [option]. [file].

Common options for ls

-an all to view all files in the directory, including hidden files

-l long list display

-h human is displayed in a humanized way

-d lists only the directory name and nothing else

-t sort by modification time

-S sorts by Size of the file

-r arrange reverse in reverse order

-I display the inode number (index number) of the file

# date-help

Usage: date [OPTION]... [+ FORMAT]

Or: date [- u |-- utc |-- universal] [MMDDhhmm [[CC] YY] [.ss]]

# date

# date +% H

# date +% F

# date 0214080019

# date 0214080019.30

# date-s 12:00

[root@tianyun ~] # touch `date +% F` _ file.txt

[root@tianyun ~] # ls

2017-07-24_file.txt

Two kinds of time:

Hardware time, i.e. motherboard BIOS time

System time, i.e. Linux system time

2. Man manual name (for command help, for configuration file help, for function help)

[root@tianyun ~] # man man

MANUAL SECTIONS

The standard sections of the manual include:

1 User Commands

2 System Calls

3 C Library Functions

4 Devices and Special Files

5 File Formats and Conventions

6 Games et. Al.

7 Miscellanea

8 System Administration tools and Deamons

Command help: section 1, section 8

Function help: chapter 2, chapter 3

File format: section 5

In general, you do not need to use a chapter number, for example:

# man ls

# man useradd

# man setfacl (/ EXAMPLES)

Tip 1: query by chapter

/ usr/bin/passwd modify user password command

/ etc/passwd profile containing user information

# man-f passwd lists the passwd manuals in all chapters

# help with the man 1 passwd passwd command

# help with man 5 passwd user profile

Tip 2: query in all chapters

# man-a passwd

The answer to the question on how to understand shell is shared here. I hope the above content can be of some help to you. If you still have a lot of doubts to solve, you can follow the industry information channel to learn more about it.

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