Shell's underlying syntax

Shell variables: Local variables and environment variables

Basic elements:

#！ /bin/bash

#

Variable

Process Control

Home: The current user's home directory

Path: The current user's executable file search path

LANG: The default language the program should use

PSI: Line Prompt

Pstree displaying processes as a directory tree

Bash--version View the version of Bash

The type command shows what command

such as: type pwd

A command line can contain more than one command, separated by semicolons.

Ls;pwd;date

Predefined variables: Store information that users don't need to care about

Set to view all local variables

Env can only view environment variables

lang=en Change the command to the English environment

Locale-a shows all languages supported by the LINX system

1. Variable A=boobooke

Input: Echo $a

Display: Boobooke

Input: Echo ${a}123

Display: boobooke123

Reset variable unset A-----Delete this variable (do not delete the variable when it is not $)

Example: #!/bin/bash

#this is .....

#name =admin

echo "${name} Welcome Boobooke"

Note: No spaces exist on both sides of the equal sign when assigning a value. Variable name = value

The value contains a space and must be enclosed in double quotation marks.

Shell variables can be written in uppercase and lowercase letters

For example 1:vi clear.sh

#！ /bin/bash

#this is clear

Cat/dev/null>/var/log/messages

echo "Logs cleaned up"

chmod +x clear.sh

./clear.sh

Command substitution such as 2:vi work.sh

#!/bin/bash

echo "Your work is directory: ' pwd '"

#注意pwd要用单引号, in the ~ key

Variable reference format: $ variable name, or ${variable name}

The variable name is one character in the way one, variable name multiple characters are suggested in mode two, for example:

A=1

abc= "Hello"

Echo $a

Echo ${ABC}

Variable extension modifier: ${variable;-word}

such as: ${name1;-ganxing}, Explanation: If the name of the variable is not name1, the output

Ganxiang

Example of positional variable parameter: #!/bin/bash

echo "This script's name is $"

echo "1th parameter is $"

echo "2nd parameter is $"

This article is from the "Day to survive, Night development" blog, please be sure to keep this source http://perter.blog.51cto.com/1962646/1840839

Shell's underlying syntax