Shell learning

Output hello world

//  Designated for /bin/bash The interpreter under 
#!/bin/bash
echo "Hello World !"

function shell There are two ways

1、 As an executable 
chmod +x ./test.sh  # Give the script permission to execute 
./test.sh  # Execute the script 

2、 As interpreter parameters 
//  choose /bin/sh Interpreter execution under  test.sh file 
/bin/sh test.sh

shell The variable of

 assignment ：
name="test name"
 Be careful name and = There must be no space between them 

 You can use statements to assign values to variables ：
for file in `ls /etc`  or  for file in $(ls /etc)

 Using variables ：
${name}

 A read-only variable :
readonly name

 Delete variables ：
unset name

 Variable type ：
	 local variable 
	 environment variable 
	shell Variable 

shell String

 String assignment ：
str='str' //  Single quotation marks 
str="str" //  Double quotes 
str=str //  No quotes 

 Get string length ：
string="abcd"
echo ${
    #string} # Output  4

 Extract substring ：
string="runoob is a great site"
echo ${string:1:4} #  Output  unoo

 Find substrings 
string="runoob is a great site"
echo `expr index "$string" io`  #  Output  4

shell Pass parameters

echo "Shell  Pass parameter instance ！";
echo " File name of execution ：$0";
echo " The first parameter is zero ：$1";
echo " The second parameter is ：$2";
echo " The third parameter is zero ：$3";

 Output 
$ chmod +x test.sh 
$ ./test.sh 1 2 3
Shell  Pass parameter instance ！
 File name of execution ：./test.sh
 The first parameter is zero ：1
 The second parameter is ：2
 The third parameter is zero ：3

shell Array

array_name=(value1 value2 ... valuen)

array_name[0]=value0
array_name[1]=value1
array_name[2]=value2

${array_name[index]}

echo " The elements of the array are : ${my_array[*]}"
echo " The elements of the array are : ${my_array[@]}"

shell Operator