my @chrnums = (
    [qw(chr1 10)],
    [qw(chr3 20)],
    [qw(chr1 30)],
    [qw(chr3 5)],  
    [qw(chr5 5)],
    );

my @s = map {
  $chrnums[(substr $_,8)]  ## 8 on architectures where a long is 4 bytes. See Config
} sort map {
  pack "LLA*", (substr $chrnums[$_][0], 3), $chrnums[$_][1], $_
} 0..$#chrnums;