I was the one that mentioned the differences between for & foreach and between exec & system in the chatterbox. My entire list is:

• for & foreach
• exec & system
• map & grep
• sysread & read
• pack & sprintf
• chop & chomp
• local & my
• time & times
• qq & qx
• rand & srand
• exists and defined
• print & printf
• perl4 & perl5
• use and require
• eval & study
• bless & tie
• select & select :)

I find this list to be a fairly good window into someone's perl skills. Some of the above are easy, some aren't even really "paired", and some are trickier than they look (e.g. the *real* differences between "my" and "local" (and "our" :) ).

Asking for sample scripts is good, as well as asking them to make a quick script on the spot. Asking them to solve a regex problem is also a nice indicator. You can fake things on your resume, but not on an actual interview "exam" ^[1] :)

It's also important to see how someone reacts to the above questions. How you handle questions you don't know or aren't sure of is very important too. You could be even throw in some answers that cannot be answered, such as asking the difference between "caller" & "sender." (The former is a rarely used, yet legitimate function, which makes the second one seem all the more likely to be legitimate too, even though it is not)

[1]It sure is easy writing about this from the "other side of the table" ;)- but it's one of the best ways to demonstrate perl knowledge, as we are not as standardized and certification-heavy as "other" IT skills (I shall name no names)