Linux Learning Summary (60) Shell script 4-Functions and arrays

A function in the shell

1 understand several system variables of the script first

$# 是传给脚本的参数个数$0 是脚本本身的名字$1 是传递给该shell脚本的第一个参数$2 是传递给该shell脚本的第二个参数[email protected] 是传给脚本的所有参数的列表$* 是以一个单字符串显示所有向脚本传递的参数，与位置变量不同，参数可超过9个$$ 是脚本运行的当前进程ID号$? 是显示最后命令的退出状态，0表示没有错误，其他表示有错误

2 definition and usage of functions
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} functions must be placed first, where the keyword function can be omitted
Example 1

vim 6.sh#!/bin/bashinput() {    echo $1 $2 $# $0}input 4 4 4 4 4

The execution result is: 4 4 5 6.sh
The first and second parameter of a shell script passed
$# indicates the number of arguments passed to the script
The name of the script itself
Example 2

#!/bin/bashsum(){s=$[$1+$2]echo $s}sum 1 2

If you want to pass in parameters outside of the script, Sum 1 2 can be changed to sum $ $, and then execute the script with parameters such as SH sum.sh 1 2
Example 3
requirements, write a script, give the network card name, you can display the corresponding IP address
Script debugging
ifconfig |grep ens33 -A1 |grep ‘inet‘ |awk ‘{print $2}‘
The meaning of each paragraph:
Ifconfig Needless to say, you can view information about the NIC
grep enss3-a1 filters out the line containing the NIC name Ens33, and prints its next line in passing. Which is the IP address line we need.
grep ' inet ' to find the line with the IP address, here you can use TAIL-1 instead
awk ' {print $} ' prints the second segment of the IP address line, which is the IP address, and awk does not specify a delimiter, which is separated by a space or tab by default. That is, split with a null character.
Final result

#!/bin/baship(){ifconfig |grep "$1: " -A1 |grep ‘inet‘ |awk ‘{print $2}‘}read -p "please input a name of network card: " nameip $name

Note: The following grep command represents the first argument passed by the function, so be sure to use double quotation marks.
Make a perfect of the above script,
1 Determine if the network card name is the network card in the system, not to give a hint
2 Determine if the NIC is assigned an IP address, no hint

#!/bin/baship(){ifconfig |grep "$1: " -A1 |grep ‘inet‘|awk ‘{print $2}‘}read -p "please input a name of network card: " nameip $namen=`ifconfig |grep "$name"`if [ -z "$n" ];then    echo "the eth is not exist"fim=`ifconfig |grep "$name" -A1 |grep ‘inet‘`if [ -z "$m" ];then    echo "the eth has no ip assigned"fi

Arrays in the two shells

Define array a= (1 2 3 4 5)
echo ${a[@]}//Show entire array, equivalent to echo ${a[*]}
echo ${#a [@]} Gets the number of elements in the array
echo ${a[2]} reads the third element, array element number starting from 0
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
Unset a[1]; echo ${a[*]}//delete 1th element in array
unset A;echo ${a[*]}//Empty array
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 then intercepts 2
Array substitution
echo ${a[@]/3/100}//replaces 3 in array A with 100 (displays only to the screen and does not change the array)
A= (${a[@]/3/100})//replace 3 in array A with 100 (change array)

Linux Learning Summary (60) Shell script 4-Functions and arrays