PHP system function

PHP The code is as follows : 

<?php

$v = system('netstat -tnlp',$shell_return);

var_dump($shell_return);
var_dump($v);

Execution results :

Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:111             0.0.0.0:*               LISTEN      1/systemd           
tcp        0      0 192.168.122.1:53        0.0.0.0:*               LISTEN      7311/dnsmasq        
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      6987/sshd           
tcp        0      0 127.0.0.1:631           0.0.0.0:*               LISTEN      6978/cupsd          
tcp        0      0 127.0.0.1:6011          0.0.0.0:*               LISTEN      16181/sshd: [email protected] 
tcp6       0      0 :::3306                 :::*                    LISTEN      7361/mysqld         
tcp6       0      0 :::111                  :::*                    LISTEN      1/systemd           
tcp6       0      0 :::8080                 :::*                    LISTEN      7689/httpd          
tcp6       0      0 :::80                   :::*                    LISTEN      7689/httpd          
tcp6       0      0 :::22                   :::*                    LISTEN      6987/sshd           
tcp6       0      0 ::1:631                 :::*                    LISTEN      6978/cupsd          
tcp6       0      0 ::1:6011                :::*                    LISTEN      16181/sshd: [email protected] 
tcp6       0      0 :::8000                 :::*                    LISTEN      7689/httpd          
int(0)
string(90) "tcp6       0      0 :::8000                 :::*                    LISTEN      7689/httpd"

The conclusion is as follows :

system($shell, $shell_return):

1. $shell: yes shell command , Such as 'netstat -tnlp'
2. $shell_return: shell Return result of command execution , If the command is executed successfully, return 0, Otherwise, no 0
3. After the function is executed , Print the result of command execution directly in the terminal window
4. The return value of the function is the last line of the execution result of the command