For clarity of instructions, we will use the following terminology.

Server = Remote system, typically like a web server
Client = Local system, the computer/vm you are using

Download file from Server

Server

Run the following command on the server.

cat file.txt | nc -l -p 1234

Client

Now on the client we can download the file with the following. Change the IP to the Server IP address

nc 192.168.1.20 1234 > file.txt

Upload from Client to Server

If we want to reverse this, aka. send a file from the client to the server, we can do the following

Server

This will write the file to file.txt

nc -l -p1234 -q 1 > file.txt < /dev/null

Client

Send file.txt to 192.168.1.20. Change the file and IP address as needed.

cat file.txt | nc 192.168.1.20 1234

https://superuser.com/questions/98089/sending-file-via-netcat