eval

eval [arg ...]
    The  args  are read and concatenated together into a single com-
    mand.  This command is then read and executed by the shell,  and
    its  exit status is returned as the value of eval.  If there are
    no args, or only null arguments, eval returns 0.
ls is reporting the allocated size; du is reporting the amount of space actually used.

https://www.digitalocean.com/community/tutorials/how-to-use-netcat-to-establish-and-test-tcp-and-udp-connections-on-a-vps
https://www.linuxtechi.com/nc-ncat-command-examples-linux-systems/
netcat
netcat [options] host port
netcat -u host port
netcat -z -v domain.com 1-1000
netcat -z -n -v 198.51.100.0 1-1000 2>&1 | grep succeeded
netcat -l 4444
netcat domain.com 4444