An efficient way to transpose a file in Bash

Question

I have a huge tab-separated file formatted like this

X column1 column2 column3
row1 0 1 2
row2 3 4 5
row3 6 7 8
row4 9 10 11

I would like t

Answer 1

#!/bin/bash

aline="$(head -n 1 file.txt)"
set -- $aline
colNum=$#

#set -x
while read line; do
  set -- $line
  for i in $(seq $colNum); do
    eval col$i="\"\$col$i \$$i\""
  done
done < file.txt

for i in $(seq $colNum); do
  eval echo \${col$i}
done

another version with set eval