Bash: Switch positions between all characters in odd positions with characters in even positions

The following awk script allowed us to switch position of all characters placed in odd numbered positions with their next neighboring even numbered position characters.
In detail what it does is to create a for loop that skips one character every time and then it prints each pair in reverse order (it will print the second character first, then the first one, then the fourth and so on).

echo "123456789" | awk -vFS= '{for (i = 1; i <= NF; i+=2) {printf $(i+1)$i""} printf "\n"}';

# Will produce 214365879

echo "1234567890" | awk -vFS= '{for (i = 1; i <= NF; i+=2) {printf $(i+1)$i""} printf "\n"}';

# Will produce 2143658709

Please note that we set the built-in variable FS (The input field separator which is a space by default) to the empty string so that each character is treated like a different field by NF (The number of fields in the current input record).