Understand shell script in one article

Article, understand shell Script

1 、shell Script Introduction

• What is? shell Script

A series of shell Collection of commands , You can also add some logical operations （if else for） Put these commands in a file .

• What is? shell command ?

  ls

  pwd

  cd

  chmod +x test.sh

• shell The basic format of the script

  • Naming format

    • General naming rules : xxxxx.sh ( It is suggested that .sh Name the suffix )

  • Writing format

    # test.sh # yes shell Comments in the script 
    #  The first line if you forget to write ,  Use the default command parser  /bin/sh
    #!/bin/bash #  Specify resolution shell The command parser used in the script  /bin/sh It's fine too 
    #  A series of shell command 
    ls
    pwd
    cp 
    rm
    

• shell Script execution

  #  perform shell Script 
  ./xxx.sh
  sh test.sh
  

  ---

2、 shell Variables in scripts

• Common variables ( The local variable )

  #  Defining variables ,  Definition complete ,  You have to assign , = No spaces before and after 
  temp=666
  #  Normal variables can only be used in the current process 
  

• environment variable —— In general capital

  #  It is understandable to ask global variables ,  It can be accessed globally in the current operating system 
  #  classification 
  	-  System native 
  		- PWD
  		- SHELL
  		- PATH
  		- HOME
  	-  User defined 
  		-  Promote normal variables to system level environment variables 
  		GOPATH=/home/zoro/go/src - >  Common environment variables 
  		set GOPATH=/home/zoro/go/src - >  System environment variable 
  		export GOPATH=/home/zoro/go/src
  		~/.bashrc
  

• Positional variable

  When executing a script , You can pass parameters to a script , Receive these parameters inside the script , You need to use position variables

#  Existing scripts test.sh
#!/bin/bash
echo "hello , world, $0"
echo " The first parameter : $1"
echo " The first 2 Parameters : $2"
echo " The first 3 Parameters : $3"
echo " The first 4 Parameters : $4"
echo " The first 5 Parameters : $5"
echo " The first 6 Parameters : $6"
#  perform test.sh
$ ./test.sh 11 22 3 4 5 6 aa bb
hello , world, ./test.sh
 The first parameter : 11
 The first 2 Parameters : 22
 The first 3 Parameters : 3
 The first 4 Parameters : 4
 The first 5 Parameters : 5
 The first 6 Parameters : 6

• Special variables
  • $#: Get the number of parameters passed
  • [email protected]: All parameters passed to the script
  • $?: The status after the script execution is completed , Failure >0 or success =0
  • $$: The corresponding process after the script process is executed ID

# test.sh
#!/bin/bash
echo "hello , world, $0"
echo " The first parameter : $1"
echo " The first 2 Parameters : $2"
echo " The first 3 Parameters : $3"
echo " The first 4 Parameters : $4"
echo " The first 5 Parameters : $5"
echo " The first 6 Parameters : $6"
echo " Number of parameters passed : $#"
echo " All parameters passed : [email protected]"
echo " The process of the current script ID: $$" 

$ ./test.sh aa bb cc dd ee ff 8 9 0 
    hello , world, ./test.sh
     The first parameter : aa
     The first 2 Parameters : bb
     The first 3 Parameters : cc
     The first 4 Parameters : dd
     The first 5 Parameters : ee
     The first 6 Parameters : ff
     Number of parameters passed : 9
     All parameters passed : aa bb cc dd ee ff 8 9 0
     The process of the current script ID: 47946
#  Script execution status view 
$ echo $?
0 ->  success 
 Not 0 ->  Failure 

• Common variable value

#  Variable definitions 
value=123	#  By default, it is processed as a string 
value1 = "123 456"
echo $value
#  How to get the value of a variable :
 - $ Variable name 
 - ${ Variable name }

• Take the result value after the command is executed

  #  There are two ways to take value :
  var=$(shell command )
  var=`shell command `
  

• Use of quotation marks

  #  Double quotes 
  echo " Current file : $var"
  -  When printing, it will var Take out the value in and output 
  #  Single quotation marks 
  echo ' Current file : $var'
  -  Output the string as it is 
  

3 、 Condition judgment and cycle

• shell Script if conditional

  # if sentence 
  #  matters needing attention :
  	- if  and  [] There is a space directly 
  	- [  Conditions  ] :  There are spaces before and after the condition 
  	- else if => elif
  	- 
  if [  conditional  ];then
  	 Logical processing  -> shell command 
  	xxx
  	xxxx
  	xxxx
  fi
  # ===================
  if [  conditional  ]
  then
  	 Logical processing  -> shell command 
  	xxx
  	xxx
  fi
  # if ... elif .. fi
  if [  conditional  ];then
  	 Logical processing  -> shell command 
  	xxx
  	xxxx
  	xxxx
  elif [  conditional  ];then
  	shell command 
  elif [  conditional  ];then
  	shell command 
  elif [  conditional  ];then
  	shell command 
  else
  	shell command 
  fi
  

  # if.sh
  #!/bin/bash
  #  You need to judge the file name passed into the script 
  if [ -d $1 ];then
      echo "$1  Is a directory !"                                                
  elif [ -s $1 ];then
      echo "$1  It's a document ,  And the file is not empty "
  else
      echo "$1  Not a directory ,  There may not be ,  Or the file size is 0"
  fi
  

  • shell Script for loop

  # shell The cycle in  for/ while
  #  grammar : for  Variable  in  aggregate ; do;done
  for var in  aggregate ;do
  	shell command 
  done
  

  # for.sh
  #!/bin/bash
  #  Traverse the files in the current directory 
  list=`ls`
  for var in $list;do
      echo " Current file : $var"
      echo ' Current file : $var'                                       
  done
  

---

4、shell Functions in scripts

#  No function modification ,  No parameters ,  no return value 
#  Format 
funcName(){
    
	#  Get the first parameter 
	arg1=$1
	#  Get the first 2 Parameters 
	arg2=$2
	 The body of the function  -> shell command  +  Logic loops and judgments 
	mkdir /root/abc
}
#  No parameter list ,  But you can pass it on 
#  Function call 
funcName aa bb cc dd
#  The state after the function call : 
0 ->  Successful call 
 Not 0 ->  Failure 

#!/bin/bash
#  Determine whether the file name passed is a directory ,  If not ,  establish ...
#  Defined function 
is_directory()
{
    
    #  Get the filename ,  Get the file name through the parameter 
    name=$1
    if [ -d $name ];then
        echo "$name  Is a directory !"
    else
        #  Create directory 
        mkdir $name
        if [ 0 -ne $? ];then
            echo " Directory creation failed ..."
            exit
        fi  
        echo " Directory created successfully !!!"                                                                                         
    fi  
}

#  Function call 
is_directory $1