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Simple Regex Samples

Discussion in 'Unix' started by lionaneesh, Mar 11, 2011.

  1. lionaneesh

    lionaneesh Active Member

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    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!
     
  2. lionaneesh

    lionaneesh Active Member

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    I hope the viewers like it!!!
     

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