erickn@cosmora01d:/home/erickn/mi> cat x
my $asdf = 'ddddd ee asdfg';
my $new = join('_',(sort {length($b) <=> length($a) || $a cmp $b} split /\s/, $asdf));
print "$new\n";
my $asdf = 'aaa bbbb c';
my $new = join('_',(sort {length($b) <=> length($a) || $a cmp $b} split /\s/, $asdf));
print "$new\n";

erickn@cosmora01d:/home/erickn/mi> perl x
asdfg_ddddd_ee
bbbb_aaa_c