That sounds like a great question to me -- ask them how they'd open a file and parse it. It may involve a bit of verbal punctuation, but you can easily wander off into the dis/advantages of using @ARGV and <> as opposed to opening the file manually, perhaps the distinction between while(<>) and while($_ = <>), error handling on the open, and a kazillion things related to parsing (roll-your-own XML parser, or use a module? DOM or SAX or XML::Parser? backslashed quotes in CSV files? when is good enough good enough? etc.)