function in shell, array in shell, demand analysis of alarm system

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
INP () {
echo "The first is $ $"
echo "The second is $"
echo "The third is $"
echo "The script is $"
echo "The number is $#"
}
INP a b c d E
This function is used to print the parameters of the

[Email protected] shell]# sh fun1.sh
The first is a
The second is B
The third is C
The script is fun1.sh
The number is 5
What we need to note here is that our function name is not the same as the command in the shell. If you are going to call a function, the generic name at the end of the script will be the same as the function name, so it can be called.

Example 2
#!/bin/bash
Sum () {
S=$[$1+$2]
Echo $s
}
Sum 1 11
Run the result as
[Email protected] shell]# sh fun2.sh
12
This is a function that defines addition, S is a variable, equals two numbers, where $ and $ are the first parameter of the function and the second argument is added.
$2 means 1,$2, $s is 1+11.

Example 3
#!/bin/bash
IP () {
Ifconfig |grep-a1 "ens33:" |grep ' inet ' |awk ' {print $} '
}
Read-p "Please input the ETH name:" ETH
IP $eth
This is a script that specifically displays the IP. A1 is the first line that displays the keywords and keywords below.
Please input the ETH name: means to display the name of the NIC.
Echo ' $e address is $myip ' is the IP that displays the network card

Run the result as
[Email protected] shell]# sh-x fun3.sh

• Read-p ' Please input the ETH name: ' ETH
  Please input the ETH name:ens33
• IP ens33
• Grep-a1 ' Ens33: '
• Ifconfig
• grep inet
• awk ' {print $} '
  192.168.218.130

Arrays in the shell

A string of strings or a string of numbers formed by a variable, called an array, we can operate on the array.
For example:
Defines the array b= (a string of numbers or strings);
Show results echo ${b[]}
[Email protected] shell]# b= (1 2 3)
[[email protected] shell]# echo ${b[]}
1 2 3

We can also view the value of an element
For example:
We want to see the value of an element
Echo ${a[2]}
[[email protected] shell]# echo ${b[2]}
3
Here is a special, array starting from 0, that is, 0 is the first element.

We can also display the number of elements
echo ${#b []} Gets the number of elements in the array, #表示元素个数.
For example:
[[email protected] shell]# echo ${#b []}
3

Array Assignment
We can also assign values to one of the elements of an array.
[Email protected] shell]# B[3]=a
[[email protected] shell]# echo ${b[]}
1 2 3 A
We have added a new element A in this, directly after the printing time, this is because the subscript does not exist will automatically add an element
can also be replaced
[Email protected] shell]# B[0]=AAA
[[email protected] shell]# echo ${b[]}
AAA 2 3 A

We can also delete the value of the array, using the unset command
[[email protected] shell]# echo ${b[]}
AAA 2 3 A
[Email protected] shell]# unset b[3]
[[email protected] shell]# echo ${b[]}
AAA 2 3

Array shards
Sometimes we want to intercept part of the array
[[email protected] shell]# echo ${a[*]}
1 2 3 4 5 6 7 8 9 10
For example
We're going to intercept from 4 to 7.

4 5 6 7
Intercept from behind

8 9
What we need to note here is that the interception from behind must be written in 0-or else it will not succeed.

Substitution of arrays
[[email protected] shell]# echo ${a[]/8/6}
1 2 3 4 5 6 7 6 9 10
We can also assign values directly
[[email protected] shell]# echo ${a[]/3/100}
1 2 100 4 5 6 7 8 9 10
[[email protected] shell]# echo ${A[*]/100/3}
1 2 3 4 5 6 7 8 9 10

Demand analysis of alarm system

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 to have log output

function in shell, array in shell, demand analysis of alarm system