# assume my(%field) exists, holding name->index pairs
# assume my(@records) exists, holding your recods

my $data = "lnum-a,source-a,hits-d,sip-d,time-a";
my %is_string = ( source => 1 );  # sort with cmp

my $sorter = make_field_sort($data, \%field, \%is_string);
for (sort $sorter @records) { ... }

sub make_field_sort {
  my ($data, $FIELD, $STRING) = @_;
  my @cmp;

  for (split /,/, $data) {
    my ($f, $o) = split /-/;
    push @cmp, ('b <=> a', 'a <=> b')[$o eq 'a'];
    $cmp[-1] =~ s/<=>/cmp/ if $STRING->{$f};
    $cmp[-1] =~ s/([ab])/\$${1}->[$FIELD->{$f}]/g;
  }

  local $" = " or ";
  eval "sub { @cmp }";
}