smahesh Re: map and grep gave a very good synopsis of the difference.

Another key difference is right there in your OP (this expands on smahesh's remark)

• grep --- use it when you want to extract certain elements of a list based on certain criteria
• map --- use this when you want to do something to every element of a list

Note with both the difference in the return value depending on the context in which it's called.

perldoc -f grep

perldoc -f map