Slackware: Summer 2009/2010

#!/bin/bash

cat << EOF > /usr/share/zoneinfo/Brazil/summer2009.zic
Rule Brazil 2009 only - Oct 18 00:00 1 S
Rule Brazil 2010 only - Feb 21 00:00 0 -

Zone Brazil/East -3:00 Brazil BR%sT
EOF

zic /usr/share/zoneinfo/Brazil/summer2009.zic

cat /etc/localtime > /etc/localtime.copy && \
rm /etc/localtime && \
ln -s /usr/share/zoneinfo/Brazil/East /etc/localtime