1, Shell Basics

Shell:Shell is a program written in C language. It is a bridge for users to use Linux. Shell is both a command language and a programming language.

Shell refers to an application that provides an interface through which users can access the services of the operating system kernel.

shell script: a script program written for the shell.

1.1 shell statement

1.1.1 shell output statement and shell comment statement

(1) Output statement echo

Display normal string

#!/bin/bash
# From above #!  Is a kind of convention tag, which can tell the system what kind of interpreter this script needs to execute;

echo "Hello, world!"

Show wrap

echo -e "OK! \n" # -e open escape
echo "It is a test"

Show no line breaks

echo -e "OK! \c" # -e enable escape \ c do not wrap
echo "It is a test

Results directed to file

echo "It is a test" > myfile

(2) comment statement

For single line notes#

multiline comment

:<<EOF
 Note Content ...
Note Content ...
Note Content ...
EOF

1.1.2 shell variables

(1) Define variables

When defining a variable, the variable name is not marked with a dollar sign

country="China"
Number=100
country="America"  #Redefine variable values

Note: 1. There must be no space between variable name and equal sign;

2. The first character must be a letter (A-Z, A-Z).

3. There can be no space in the middle. You can use underscore ().

4. Punctuation cannot be used.

5. The keyword in bash cannot be used

(2) Use variables

It is OK to add the dollar sign $in front of a defined variable. In addition, the {} of the variable is optional. Its purpose is to help the interpreter identify the boundary of the variable.

country="China"
echo $country
echo ${country}
echo "I love my ${country}abcd!"  

(3) Delete variable

unset variable_name

1.1.3 shell string

(1) Define string

String is the most commonly used and useful data type in shell programming (there are no other types to use except numbers and strings). String can use single quotation marks, double quotation marks or no quotation marks.

str='this is a string' #Single quote string

#Double quotation mark definition string
your_name="runoob"
str="Hello, I know you are \"$your_name\"! \n"
echo -e $str

• You can have variables in double quotes
• Escape characters can appear in double quotation marks

(2) Splice string

your_name="runoob"
# Use double quotation mark splicing
greeting="hello, "$your_name" !"
greeting_1="hello, ${your_name} !"
echo $greeting  $greeting_1

(3) Get string length, extract string, find string

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

#Extract substring
string="runoob is a great site"  #Intercept 4 characters from the second character of the string:
echo ${string:1:4} # Output unoo

#Find string
string="runoob is a great site" #Find the position of the character i or o (calculate which letter appears first)
echo `expr index "$string" io`  # Output 4

Note: in the above script, ` is a backquote, not a single quote '.  

1.1.4 shell array

(1) Define array

array_name=(value0 value1 value2 value3)

Define arrays individually

array_name[0]=value0
array_name[1]=value1
array_name[n]=valuen

(2) Read array

The general format for reading array element values is:

${array name [subscript]}

valuen=${array_name[n]}

Use the @ symbol to get all the elements in the array

echo ${array_name[@]}

(3) get array length

# Gets the number of array elements
length=${#array_name[@]}

1.1.5 shell operators

(1) Arithmetic operation

expr is an expression evaluation tool, which can be used to evaluate expressions.

a=10
b=20
expr $a + $b
expr $a - $b
expr $a \* $b
expr $a / $b
expr $a % $b
a=$b

Or:

a=10
b=20

val=`expr $a + $b`
echo "a + b : $val"

val=`expr $a - $b`
echo "a - b : $val"

val=`expr $a \* $b`
echo "a * b : $val"

val=`expr $b / $a`
echo "b / a : $val"

val=`expr $b % $a`
echo "b % a : $val"

if [ $a == $b ]
then
   echo "a be equal to b"
fi
if [ $a != $b ]
then
   echo "a Not equal to b"
fi

(2) Relational operator

 

a=10
b=20

if [ $a -eq $b ]
then
   echo "$a -eq $b : a be equal to b"
else
   echo "$a -eq $b: a Not equal to b"
fi
if [ $a -ne $b ]
then
   echo "$a -ne $b: a Not equal to b"
else
   echo "$a -ne $b : a be equal to b"
fi
if [ $a -gt $b ]
then
   echo "$a -gt $b: a greater than b"
else
   echo "$a -gt $b: a Not greater than b"
fi
if [ $a -lt $b ]
then
   echo "$a -lt $b: a less than b"
else
   echo "$a -lt $b: a Not less than b"
fi
if [ $a -ge $b ]
then
   echo "$a -ge $b: a Greater than or equal to b"
else
   echo "$a -ge $b: a less than b"
fi
if [ $a -le $b ]
then
   echo "$a -le $b: a Less than or equal to b"
else
   echo "$a -le $b: a greater than b"
fi

Output results:

10 -eq 20: a is not equal to b
 10 -ne 20: a is not equal to b
 10 -gt 20: a not greater than b
 10 -lt 20: a less than b
 10 -ge 20: a less than b
 10 -le 20: a less than or equal to b

(3) Boolean operation

a=10
b=20

if [ $a != $b ]
then
   echo "$a != $b : a Not equal to b"
else
   echo "$a == $b: a be equal to b"
fi
if [ $a -lt 100 -a $b -gt 15 ]
then
   echo "$a Less than 100 and $b Greater than 15 : return true"
else
   echo "$a Less than 100 and $b Greater than 15 : return false"
fi
if [ $a -lt 100 -o $b -gt 100 ]
then
   echo "$a Less than 100 or $b Greater than 100 : return true"
else
   echo "$a Less than 100 or $b Greater than 100 : return false"
fi
if [ $a -lt 5 -o $b -gt 100 ]
then
   echo "$a Less than 5 or $b Greater than 100 : return true"
else
   echo "$a Less than 5 or $b Greater than 100 : return false"
fi

Output results

10 !=  20: A is not equal to b
 10 less than 100 and 20 more than 15: return true
 10 less than 100 or 20 greater than 100: returns true
 10 less than 5 or 20 greater than 100: false is returned

(4) Logical operation

a=10
b=20

if [[ $a -lt 100 && $b -gt 100 ]]
then
   echo "return true"
else
   echo "return false"
fi

if [[ $a -lt 100 || $b -gt 100 ]]
then
   echo "return true"
else
   echo "return false"
fi

1.1.6 shell judgment statement

Including: 1. if [expression] then # statement # fi

2. if [expression] then statement else statementfi

3. if [expression] then statement... Elif [expression] then statement elif [expression] then statement... fi

a=10
b=20
if [ $a == $b ]
then
   echo "a is equal to b"
else
   echo "a is not equal to b"
fi

$in shell script? It refers to the successful or failed status of the last command execution. If success is 0, failure is 1. The statement if [$? - EQ 0] is the last command to judge the if statement. If the execution is successful, execute the statement in if, otherwise execute the content in else.

cd u-boot 
if [ $? -eq 0 ]; then
		echo "====Build uboot ok!===="
else
		echo "====Build uboot failed!===="
		exit 1
fi

(1) if statement

if condition
then
    command1 
    command2
    ...
    commandN 
fi

(2) if else statement

if condition
then
    command1 
    command2
    ...
    commandN
else
    command
fi

(3) if else -if else statement

if condition1
then
    command1
elif condition2 
then 
    command2
else
    commandN
fi

(4) case statement

echo 'Enter a number between 1 and 4:'
echo 'The number you entered is:'
read aNum
case $aNum in
    1)  echo 'You chose 1'
    ;;
    2)  echo 'You chose 2'
    ;;
    3)  echo 'You chose 3'
    ;;
    4)  echo 'You chose 4'
    ;;
    *)  echo 'You didn't enter a number between 1 and 4'
    ;;
esac

1.1.7 circular statements

(1) for loop statement

General format:

for variable in list
do
    command1
    command2
    ...
    commandN
done

Usage:

for loop in 1 2 3 4 5
do
    echo "The value is: $loop"
don

(2) while loop statement

#!/bin/bash
int=1
while(( $int<=5 ))
do
    echo $int
    let "int++"
done

1.1.8 shell transfer parameters

#!/bin/bash

echo "Shell Pass parameter instance!";
echo "Executed file name: $0";
echo "The first parameter is: $1";
echo "The second parameter is: $2";
echo "The third parameter is: $3";

$ chmod +x test.sh 
$ ./test.sh 1 2 3
 Shell pass parameter instance!
Executed file name:/ test.sh
 The first parameter is: 1
 The second parameter is: 2
 The third parameter is: 3

1.1.9 shell functions

(1) Parameter function not found

demoFun(){
    echo "This is my first shell function!"
}
echo "-----Function starts execution-----"
demoFun
echo "-----Function execution completed-----"

(2) Function with parameters

funWithParam(){
    echo "The first parameter is $1 !"
    echo "The second parameter is $2 !"
    echo "The tenth parameter is $10 !"
    echo "The tenth parameter is ${10} !"
    echo "The eleventh parameter is ${11} !"
    echo "The total number of parameters is $# One! "
    echo "Output all parameters as a string $* !"
}
funWithParam 1 2 3 4 5 6 7 8 9 34 73

2, docker statement

(1)docker load

docker load command to import image files * tar, which is generally exported by the docker save command.

docker load -i test.tar
// Or the following code, equivalent effect
docker load < test.tar

-- input, - I: Specifies the imported file

3, Container installation scripting

docker -v | grep "version"
if [ $? -eq 0 ] ;then
	 systemctl start docker #! Start docker service
	 docker load -i test.tar #! Import mirror
	 docker run -dit --name   #! Start container
	 systemctl daemon-reload

	 docker logs -f -t test
else  
	echo " docker is not exist"
fi  
  

reference:

[1]shell script under linux (basic)

shell script under linux (basic) - great Xia Yin - blog Garden

[2] Shell passing parameters | rookie tutorial