If you work with rpm-based systems you will probably have seen content like this in the repo config files:

[base]
name=CentOS-$releasever - Base
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os&infra=$infra
#baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

The items in bold are yum variables.

Today, I needed to install i386 packages on a system running an x86_64 kernel (don't ask!).

Here's how I did it:

echo i386 > /etc/yum/vars/basearch

Documentation here: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/deployment_guide/sec-using_yum_variables

I had a utility server running RHEL 6.2 (I installed it as part of a RHEV evaluation process). However, I have no RHEL entitlements so am not able to get updates.

So, I converted it to CentOS 6.2, with a little help from this post:

yum clean all
mkdir ~/centos
cd ~/centos
wget http://mirror.centos.org/centos/6.2/os/x86_64/RPM-GPG-KEY-CentOS-6
wget http://mirror.centos.org/centos/6.2/os/x86_64/Packages/centos-release-6-2.el6.centos.7.x86_64.rpm
wget http://mirror.centos.org/centos/6.2/os/x86_64/Packages/yum-3.2.29-22.el6.centos.noarch.rpm
wget http://mirror.centos.org/centos/6.2/os/x86_64/Packages/yum-utils-1.1.30-10.el6.noarch.rpm
wget http://mirror.centos.org/centos/6.2/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.30-10.el6.noarch.rpm
rpm --import RPM-GPG-KEY-CentOS-6
rpm -e --nodeps redhat-release-server
rpm -e yum-rhn-plugin rhn-check rhnsd rhn-setup
rpm -Uhv --force *.rpm
yum upgrade
reboot

Nice!