Learn the shell script

First line: #!/bin/bash--#! Interpreter for Tag script

Script: #!/bin/bash

echo "Hello World"

Give execute permission chmod +x./test.sh

Execute script:./test.sh

The $ symbol is not required when defining a variable: td= ' Date ' +%y%m%d '

1. There can be no spaces between the variable name and the symbol
2. The first character must be a letter
3. The middle cannot have the space, can use the dash (_)
4. Punctuation and keywords in bash are not available

In addition to displaying assignments, you can also use statements to assign values directly to variables

For file in ' ls/etc ' to loop the file name in/etc directory

With a defined variable, just precede the variable name with the $ symbol to echo $TD or Echo ${TD}

The same variable name can be assigned two times eg:td= ' date ' +%m%d "'

Read-only variable: readonly defines variable as read-only variable, variable value cannot be changed

Url= "Http://www.baidu.com"

ReadOnly URL

Url= "http://www.tx.com"--Error

Delete variable: unset variable_nae, cannot delete read-only variable

Shell has three variables: ① local variable: defined in script or command, only valid in current script
② environment variables: All programs are valid
③shell variables: Variables set by shell programs, with local and environment

A single quote string cannot have a variable, cannot do character escaping, and double quotation marks can be implemented.

Your_name= "World"

Stitching string greeting= "Hello,${your_name}!"

get string length ${#greeting}

extract 1-4 of the string, subscript starting from 0 ${#greeting: 1:4}

Find string $ (expr index "${greeting}" world)

Reverse quotation marks for command substitution: td= ' date ' +%y%m%d ' ' Equals $ (date "+%y%m%d")

./test.sh 1 2 3

File name executed: +---/test.sh

The first parameter is:--1

The second parameter is: $2

The third parameter is: $3-+

The number of parameters is: $#-3

The current process that the script runs id:$$-->8010

Show all parameters passed: $*-->1 2 3

$* and [email protected] Difference: $* equivalent to "1 2 3", equivalent to pass a parameter, [email protected] equivalent to "1" "2" "3" equivalent to pass three parameters

Variable_name

Learn the shell script