Check ubuntu release version from command line

This info is stored in /etc/lsb-release file:

baban@ubuntu :~$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=9.04
DISTRIB_CODENAME=jaunty
DISTRIB_DESCRIPTION="Ubuntu 9.04"

You can also use lsb_release command with -a argument, which shows all info:

baban@ubuntu :~$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 9.04
Release: 9.04
Codename: jaunty
baban@ubuntu :~$