Just to expand a little on this: map, grep, foreach and most while constructs all work on perl's concept of lists. 

while (<SOME_FILE_HANDLE>)

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is special. it does not act like any other iteration construct, not even like any other while() construct. It explicitly iterates over each record ("line") one by one instead of converting the whole file to a list first.

"What should it profit a man, if he should win a flame war, yet lose his cool?"

In reply to Re^2: Different behaviors between "while" and "map" by Joost
in thread Different behaviors between "while" and "map" by lightoverhead

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