HackerRank Sed command #5 problem solution

In this HackerRank Sed command #5 problem solution we have given an input file, with N credit card numbers, each in a new line, your task is to reverse the ordering of segments in each credit card number. Assume that the credit card numbers will have 4 space-separated segments with 4 digits each.

If the original credit card number is 1434 5678 9101 1234, transform it to 1234 9101 5678 1434.

Useful References: This particular page on StackOverflow has a relevant example about sed, groups and backreferences. Here's a detailed tutorial covering groups and backreferences.

Input Format

N credit card numbers, each in a new line, credit card numbers will have 4 space-separated segments with 4 digits each.

Constraints

1 <= N <= 20

However, the value of N does not matter while writing your command.

Output Format

N lines, each containing a credit card number with the ordering of its segments reversed.

Problem solution.

sed -E 's/([0-9]{4})\ ([0-9]{4})\ ([0-9]{4})\ ([0-9]{4})/\4\ \3 \2 \1/'

Second solution.

cat /dev/stdin | sed -r 's/([0-9]{4}) ([0-9]{4}) ([0-9]{4}) ([0-9]{4})/\4 \3 \2 \1/g'

Third solution.

sed 's/\([0-9]*\) \([0-9]*\) \([0-9]*\) \([0-9]*\)/\4 \3 \2 \1/'

Fourth solution.

cat - > input
sed 's/\([0-9]*\) \([0-9]*\) \([0-9]*\) \([0-9]*\)/\4 \3 \2 \1/' input