nginx set variable value to command output

I need to set a variable value to commmand output result on nginx is it possible? Something like this

location /uploads { 
 set $test $(ls -la /home/admin | wc -l)

}

This is a command example so this command if a execute on CLI it return the number 5 so the var on nginx should have the value 5 but it doesn´t work on nginx using $ output.

Is there any posibility to get it on nginx?