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  1. Prepare
  2. Linux Shell
  3. Grep Sed Awk
  4. 'Sed' command #5

'Sed' command #5

Sed is a popular utility which enables quick parsing and transformation of text.

Here are some very simple examples of sed in action.

Substitute the first occurrence of 'editor' with 'tool'. 

`$:~/hackerrank/bash/grep/grep1$` echo "My favorite programming editor is Emacs. Another editor I like is Vim." | sed -e s/editor/tool/
My favorite programming tool is Emacs. Another editor I like is Vim.

Substitute all the occurrences of 'editor' with 'tool'. 

`$:~/hackerrank/bash/grep/grep1$` echo "My favorite programming editor is Emacs. Another editor I like is Vim." | sed -e s/editor/tool/g
My favorite programming tool is Emacs. Another tool I like is Vim.

Substitute the second occurrence of 'editor' with 'tool'. 

`$:~/hackerrank/bash/grep/grep1$` echo "My favorite programming editor is Emacs. Another editor I like is Vim." | sed -e s/editor/tool/2
My favorite programming editor is Emacs. Another tool I like is Vim.

Highlight all the occurrences of 'editor' by wrapping them up in brace brackets. 

`$:~/hackerrank/bash/grep/grep1$` echo "My favorite programming editor is Emacs. Another editor I like is Vim." | sed -e s/editor/{\&}/g
My favorite programming {editor} is Emacs. Another {editor} I like is Vim.

Some references for learning about sed have been included:
Sed - An Introduction and a tutorial
The TLDP Guide
Some Practical Examples

Task

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

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.

Sample Input

1234 5678 9101 1234  
2999 5178 9101 2234  
9999 5628 9201 1232  
8888 3678 9101 1232

Sample Output

1234 9101 5678 1234  
2234 9101 5178 2999  
1232 9201 5628 9999  
1232 9101 3678 8888

Explanation

The order of the four segments in the (input) credit card numbers have been reversed.