Sed command 4#

Overview#

sed is a popular utility that enables quick parsing and transformation of text.

Here are some basic uses for it:

Substitute the first occurrence of editor with tool:

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 occurrences of editor with tool:

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:

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 occurrences of editor by enclosing them in curly brackets (i.e., {}):

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.

Task#

Given \(N\) lines of credit card numbers, mask the first \(12\) digits of each credit card number with an asterisk (i.e., *) and print the masked card number on a new line. Each credit card number consists of four space-separated groups of four digits. For example, the credit card number 1234 5678 9101 1234 would be masked and printed as **** **** **** 1234.

References#

You may find the following links helpful in learning about sed:

Sed: An Introduction and Tutorial
The TLDP Guide
Some Practical Examples
A StackOverflow question on a slightly modified version of this task where the solution involves back references.
A tutorial from TheGeekStuff detailing the use of groups and back references.

Input Format#

Each line contains a credit card number in the form dddd dddd dddd dddd, where \(d\) denotes a decimal digit (i.e., \(0\) through \(9\)). There are a total of \(n\) lines of credit card numbers.

Constraints#

\(1 <= n <= 20\); note that the value of \(n\) does not matter when writing your command.

Output Format#

For each credit card number, print its masked version on a new line.

Sample Input#

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

Sample Output#

**** **** **** 1234 **** **** **** 2234 **** **** **** 1232 **** **** **** 1232

Explanation#

Observe that the first twelve digits have been masked for each credit card number, and they are printed in the same order as they were received as input.

Solution#

This problem is about selecting groups and replacing them. Because the card numbers are uniformly input with spaces between each group of four, you only need to select three groups of four digits and replace them with twelve asterisks separated by spaces at the appropriate points as well as one at the end of the line.

#!/usr/bin/env bash

# shellcheck disable=SC2162
sed -e 's/\([0-9]\{4\}\s\)\{3\}/**** **** **** /' -

Sed command 4

Contents