Shell Programming and Scripting

awk -F"\t" 'NR==1{nl=split($0,lines);next} {for(i=4;i<=nl;i++) print lines[i],$1"__"$2"__"$3,$i}' tmp | sort -k1.2,1n

awk -F"\t" '
NR==1{nl=split($0,lines);next}
{for(i=4;i<=nl;i++) out[i]=(((i in out) ? (out[i] RS) : "") $1 "__" $2 "__" $3 " " $i)}
END {for (i=4;i<=nl;i++) {o=out[i];gsub(RS,(RS lines[i] OFS),o);print lines[i],o}}
' tmp

#!/bin/bash
inputfile=tmp
IFS=$'\t' read -a lines < $inputfile
for ((i=4; i<=${#lines[@]}; i++))
do
  awk -F "\t" -v col=$i -v name="${lines[i-1]}" 'NR>1 {print name,($1 "__" $2 "__" $3),$col}' $inputfile
done