I don't understand why you are doing split twice (first for the row and then for the column). If you just want to return a given column from a CSV you could do it simply with:

my @result = map { 
    my @row = split /,/ => $_; 
    $row[$column_number] } @lines;
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assuming there isn't any escaped csv-values such as

a,b,"hello, world",c,d
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