You can read about split by typing:

perldoc -f split
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Set the LIMIT of split to -1 to preserve trailing nulls.

open ALL, "alltrans.csv" or die "Can not open file: $!";
while (<ALL>) {
    chomp;
    push @alltrans, [ split /,/, $_, -1 ];
}
close ALL;
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I would even write it as a one-liner, but that's a matter of personal taste:

my @alltrans;
chomp, push @alltrans, [ split /,/, $_, -1 ] for <ALL>;

# or

my @alltrans = map { chomp; [ split /,/, $_, -1 ] } <DATA>;
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