replace a whole word with different text

The following examples replaces the whole word unidad with lección in a po file.
perl -p -i.bak -e 's/\bunidad\b/lección/g' wwwroot/app/locale/es_mx/LC_MESSAGES/default.po

the /b is used to match a "word boundary"

Behind the pesky HDMI cable

http://www.freedom-to-tinker.com/?p=1005
talks about the DHCP protocol used by HDMI compatible devices, and of course how it can be broken.