gistfile1.sh

$ cat in.txt 
1000,1030
1000,1040
1040,1000
3000,3010
3010,3000


# with ruby
cat in.txt  | ruby -n -e 'BEGIN{@a = {}}; x,y = $_.chomp.split(","); if y && x && ! y.empty? then @a[x] = y; puts $_  ; end ; END{@a.keys.each{|k| puts k + "," + k}}'


# with awk
for e in `awk 'BEGIN{RS=","}{print $1}' < in.txt | sort | uniq ` ; do echo $e,$e; done && cat in.txt | sort -u

# with cut
(for e in `cut -d, -f1 < in.txt ` ; do echo $e,$e; done && cat in.txt) | sort -u

# Champion: cut + xargs
(cut -d, -f1 < in.txt | xargs -n1 -I{} echo {},{}) && cat in.txt  | sort -u