Sadly they are not portable due to the endianness of the source data and then the endianness of the destination reader system. You can find 3 diffferent ways to unpack hex strings in faq4 from memory (using hex, pack/unpack, and Bit::Vector])

As you may have noted BrowserUk presented a method that converts the data given from the OPs system (big endian) to his system (little endian wintel). When the OP tried to run it he found it broken.

Pack/Unpack Tutorial (aka How the System Stores Data) by pfaut is an excellent resource for understanding pack/unpack.