20.16/20.17 function in Shell 20.18 array 20.19 Alarm system requirements in the shell

20.16/20.17 functions in the shell
The function is to organize a piece of code into a small unit, and give the small unit a name, when the code is used to call the name of the small unit directly. Format: function F_name () {?????????????? command????????} The function has to be on the front
Example 1
#!/bin/bash
Input () {
? ? echo $ $#
}

Input 1 A B

Example 2
#!/bin/bash
Sum () {
? ? S=$[$1+$2]
? ? Echo $s
}
Sum 1 2

Example 3
#!/bin/bash
IP () {
Ifconfig |grep-a1 "$:" |awk '/inet/{print $} '
}
Read-p "Please input ip_name:" ETH
IP $eth

20.18 Arrays in the shell
Define array a= (1 2 3 4 5); Echo ${a[@]}
echo ${#a [@]} Gets the number of elements in the array
echo ${a[2]} reads the third element, array starting from 0
echo ${a[*]} equals ${a[@]} displays the entire array
Array Assignment
a[1]=100; Echo ${a[@]}
a[5]=2; Echo ${a[@]} An element is added automatically if the subscript does not exist
Deletion of arrays
Uset A; Unset A[1]

Array shards
A= ( seq 1 5 )
Echo ${a[@]:0:3} starts with the first element and intercepts 3
Echo ${a[@]:1:4} starts with the second element and intercepts 4
Echo ${a[@]:0-3:2} Starts from the bottom 3rd element and intercepts 2
Array substitution
Echo ${a[@]/3/100}
A= (${a[@]/3/100})

20.19 Alarm system Requirements Analysis
Requirements: Use the shell to customize a variety of personalized alarm tools, but the need for unified management, standardized management.
Idea: Specify a script package that contains the main program, subroutine, configuration file, mail engine, output log, and so on.
Main program: As the entire script portal, is the lifeblood of the entire system.
Configuration file: is a control center that uses it to switch individual subroutines, specifying each associated log file.
Subroutine: This is the real monitoring script, used to monitor each indicator.
Mail Engine: It is implemented by a Python program that defines the server to which the message is sent, the person who sent it, and the sender's password
Output log: The entire monitoring system should have a log output.

20.16/20.17 function in Shell 20.18 array 20.19 Alarm system requirements in the shell