Hmmm, as a non-newbie of other programming languages, you surely know the difference between the return value of a function, and its side-effects?

I'm a bit baffled by the question - it's not that you assume chomp leaves its arguments untouched and returns the the chopped lines - then you would have written the first fragment as

my @lines = chomp(<STDIN>);
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which would result in an error.