如何使用psysh php执行系统命令？

Can anyone tell me how to execute system commands E.g ls -la, whoami and etc... using psy Shell v0.9.9 (PHP 7.2.10 - cli) by Justin Hileman on linux ?

Currently when I do: shell_exec('whoami') or exec() i am getting below error:

PHP Fatal Error: Call to undefined funcion exec() in Psy Shell code on line 1

Wrap the command in backticks.

>>> `date`
=> "Tue Jul  9 11:18:27 EDT 2019
"

You can also interpolate variables:

>>> $cmd = 'date';
=> "date"
>>> `$cmd`
=> "Tue Jul  9 11:20:07 EDT 2019
"

Source: https://github.com/bobthecow/psysh/wiki/Shell-integration