8.4.3. Using Yum Variables

You can use and reference the following built-in variables in yum commands and in all Yum configuration files (that is, /etc/yum.conf and all .repo files in the /etc/yum.repos.d/ directory):
$releasever
You can use this variable to reference the release version of Red Hat Enterprise Linux. Yum obtains the value of $releasever from the distroverpkg=value line in the /etc/yum.conf configuration file. If there is no such line in /etc/yum.conf, then yum infers the correct value by deriving the version number from the redhat-release-server package. The value of $releasever typically consists of the major release number and the variant of Red Hat Enterprise Linux, for example 6Client, or 6Server.
$arch
You can use this variable to refer to the system's CPU architecture as returned when calling Python's os.uname() function. Valid values for $arch include i686 and x86_64.
$basearch
You can use $basearch to reference the base architecture of the system. For example, i686 machines have a base architecture of i386, and AMD64 and Intel 64 machines have a base architecture of x86_64.
$YUM0-9
These ten variables are each replaced with the value of any shell environment variables with the same name. If one of these variables is referenced (in /etc/yum.conf for example) and a shell environment variable with the same name does not exist, then the configuration file variable is not replaced.
To define a custom variable or to override the value of an existing one, create a file with the same name as the variable (without the “$” sign) in the /etc/yum/vars/ directory, and add the desired value on its first line.
For example, repository descriptions often include the operating system name. To define a new variable called $osname, create a new file with “Red Hat Enterprise Linux” on the first line and save it as /etc/yum/vars/osname: 
~]# echo "Red Hat Enterprise Linux" > /etc/yum/vars/osname
Instead of “Red Hat Enterprise Linux 6”, you can now use the following in the .repo files: 
name=$osname $releasever