Talk To NXT (t2n)

t2n is simple command-line tool for sending commands to nxt through the USB port, try t2n -help:

t2n version 0.0
usage: t2n [options] | t2n -help
recognized options:
-b          : check battery level
-i          : print nxt info
-ls         : list files
-put <file.rxe> : upload file
-get <file.rxe> : download file
-v          : set verbose mode
-vv         : even more verbose
-vvv        : gossip
-help       : print help and return
-version    : print version and return

t2n-0.5.tgz contains two versions: a dynamic executable, and a static one.
t2n-0.5.src.tgz contains the source code (lgpl).

Note that:

Your linux version must have USB support
The dynamic version requires lots of "so" (try ldd t2n)
Setting correct rights for USB is rather tricky. I found that the "hotplug" solution was the simplest one :

put "lego_usb.sh" and "lego_usb.usermap" in /etc/hotplug/usb
If it does not work you will need to use t2n as root ...

Links

Official Lego Mindstorm page

Nbc/Nxt page