# comparison routine for sort() assumes (for fun) that col1 and col3 are
# alpha, and col2 is numeric.  Obviously this would have to reflect the data
sub by_first_3_cols {
  $a->[0] cmp $b->[0] ||  # first, compare col1
  $a->[1] <=> $b->[1] ||  # if equal, compare col2
  $a->[2] cmp $b->[2];    # if equal, compare col3
}

# sort list of arrayrefs, each containing data from one line of input
my @sorted = sort by_first_3_cols
                  map { chomp;
                        my @columns = split /,/;
                        [ @columns ] }
                  <DATA>;

# now print sorted list in CSV format (or whatever)
print join( ',', @$_), "\n" for @sorted;