Go4Expert - Simple Regex Samples

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!