How to have the sed output side by side?

Question

I want to have standard output for KEGG pathways of a gene placed side by side no matter how many lines of the KEGG pathways it has. For example, a gene TT123456 is involves in

Answer 1

Using awk:

awk 'ORS="\t"' file

$ awk 'ORS="\t"' file
Valine, leucine and isoleucine degradation      Histidine metabolism    Ascorbate and aldarate metabolism       Lysine degradation      Glycerolipid metabolism 

If you wish to use sed then:

$ sed ':a;N;s/\n/\t/;ba' file
Valine, leucine and isoleucine degradation      Histidine metabolism    Ascorbate and aldarate metabolism       Lysine degradation      Glycerolipid metabolism