Converting timestamps across timezones

[Christopher Culver]

A script that I'm writing pulls the system time off of an iPod
connected to the computer. The iPod's time is represented as a Unix
timestamp (seconds since the epoch), but this timestamp does not
represent UTC time, but rather the local timezone of the owner. I need
to convert this local time timestamp into a UTC timestamp by referring
to the timezone specified by /etc/localtime on the computer.

I've read through the docs, but I'm rather lost on how to pull this
particular operation off. Any advice would be appreciated.