Regular expressions commonly known as ‘regex’ provide an abstract and Flexible means to compare strings. It’s mainly used for scrapping and extraction of useful data from strings. In this tutorial we’ll be looking at some regular expressions using grep in Unix/Linux and how to use them in various situations. Expressions How to parse out simple emails from body of a list of emails in your inbox A simple email list:- Code: From: lionaneesh@gmail.com To : s123@abc.com Hey Buddy!!!!!!!!! From : 123@go4expert.com To : 234@gmail.com How is the article From : test@go4expert.com To : test@gmail.com I am a test email Our target will be to parse out 'From:' types in our email list. Parse expression:- Code: cat mail.txt | grep "^From:*" Output:- Code: From: lionaneesh@gmail.com From : 123@go4expert.com From : test@go4expert.com Find all the words starting with a small letter (non-capitalized) in a given file small.txt Code: aneesh Aneesh Dogra dogra lioanneesh Lionaneesh Regex :- Code: cat small.txt | grep "^[a-z]" Output :- Code: aneesh dogra lioanneesh Find all the valid emails in a given text file emails.txt Code: lionaneesh@gmail.com hello@gmail.com hell@@gmail.com hell!@gmail..com invalid@gmail.comnop Regex :- Code: cat emails.txt | grep "[a-zA-Z0-9._%+-]\+@[a-zA-Z0-9.-]\+\.[a-z]\{2,4\}$ output:- Code: lionaneesh@gmail.com hello@gmail.com Find all the words in a given file that starts with ‘a’ and ends with ‘h’.. sample_file.txt Code: aneesh shabbir coderzone go4expert anish Regex :- Code: cat sample_file.txt | grep "^[aA].*[hH]$" Output :- Code: aneesh anish Eminem is searching for some rhyming words to pull off his rap song..Make him a regex to find some rhyming words rhyming with :- 'life' We'll be using Unix words text file to pull off this scenario... Regex :- Code: cat /usr/share/dict/words | grep "ife$" Output :- Code: Recife Yellowknife afterlife fife fishwife housewife jackknife knife life midwife nightlife penknife pocketknife rife strife wife wildlife Crypt0n is cracking a hash he has figured out that the password starts with j and ends with 2 z's... Make a regex for him to help him with his cracking Regex :- Code: cat /usr/share/dict/words | grep "[j].*[z]\{2\}$" output :- Code: jazz That’s all for this tutorial…Stay tuned for more!
