or, if I suspected that the "SHEET" could point to a very big file,

my @lines;
chomp, push @lines, [split] for <SHEET>;
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I personally believe that it wouldn't make a difference, unless you're already running Perl 6 since it has lazy evaluation by default; but in that case the syntax for the iterator would be completely different. Under Perl 5 you probably mean:

my @lines;
chomp, push @lines, [split] while <$sheet>;
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(This reply is intended mostly for the benefit of the OP which is also the reason why I incidentally changed the filehandle to a lexical variable which is what one should use in most cases nowadays.)