Why would anyone with only the CLI at his/her disposal be unsure about the available bandwidth? If you're running a server on a machine at home with the CLI only, you probably have another, GUI-enabled computer on which you can do all kinds of silly tests. If your server is located in a datacenter, you hopefully know what you're paying for.
Anyway, if you only have the CLI, you can use
wget,
ftp or
mc and many many more programs.