Bash grep sed awk

1. grep

Hackerrank Problem: Given an input file, with N credit card numbers, each in a new line, your task is to grep out and output only those credit card numbers which have two or more consecutive occurrences of the same digit (which may be separated by a space, if they are in different segments).

1234 5678 910[1] [1]234
2[9][9][9] 5178 9101 [2][2]34
[9][9][9][9] 5628 920[1] [1]232
8482 3678 9102 1232

2. AWK

References:

• https://qpeng.org/computer/grep.htm

• https://man7.org/linux/man-pages/man1/grep.1.html

References:

• https://man7.org/linux/man-pages/man1/awk.1p.html

• https://www.thegeekstuff.com/2010/01/awk-introduction-tutorial-7-awk-print-examples/

• https://www.thegeekstuff.com/2010/02/awk-conditional-statements/

• https://www.thegeekstuff.com/2010/01/8-powerful-awk-built-in-variables-fs-ofs-rs-ors-nr-nf-filename-fnr/

3. SED

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 backreferences.

• A tutorial from TheGeekStuff detailing the use of groups and backreferences.