Exec function of PHP

The code is as follows :

<?php

$out = ['a'=>'apple','b'=>'banana','c'=>'cat','d'=>'dog'];
$shell_return=null;
$v = exec('netstat -tnlp',$out,$shell_return);

print_r($out);
var_dump($shell_return);
var_dump($v);

The output after execution is as follows :

Array
(
    [a] => apple
    [b] => banana
    [c] => cat
    [d] => dog
    [0] => Active Internet connections (only servers)
    [1] => Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
    [2] => tcp        0      0 0.0.0.0:111             0.0.0.0:*               LISTEN      1/systemd
    [3] => tcp        0      0 192.168.122.1:53        0.0.0.0:*               LISTEN      7311/dnsmasq
    [4] => tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      6987/sshd
    [5] => tcp        0      0 127.0.0.1:631           0.0.0.0:*               LISTEN      6978/cupsd
    [6] => tcp        0      0 127.0.0.1:6011          0.0.0.0:*               LISTEN      16181/sshd: [email protected]
    [7] => tcp6       0      0 :::3306                 :::*                    LISTEN      7361/mysqld
    [8] => tcp6       0      0 :::111                  :::*                    LISTEN      1/systemd
    [9] => tcp6       0      0 :::8080                 :::*                    LISTEN      7689/httpd
    [10] => tcp6       0      0 :::80                   :::*                    LISTEN      7689/httpd
    [11] => tcp6       0      0 :::22                   :::*                    LISTEN      6987/sshd
    [12] => tcp6       0      0 ::1:631                 :::*                    LISTEN      6978/cupsd
    [13] => tcp6       0      0 ::1:6011                :::*                    LISTEN      16181/sshd: [email protected]
    [14] => tcp6       0      0 :::8000                 :::*                    LISTEN      7689/httpd
)
int(0)
string(90) "tcp6       0      0 :::8000                 :::*                    LISTEN      7689/httpd"

Conclusion :

exec($shell, $output, $shell_return)

1. $shell:  shell command , Such as : 'netstat -tnlp'
2. $output:  perform shell Output after command , Be careful : If $output There was value before , After appending the output data to the original data
3. $shell_return:  shell Command execution results , If it works , return 0, Failed to another value
4. exec Return value after function execution : return $output The last data of the array