REGEX - It's a Piece of Cake!

REGEX - It's a Piece of Cake!

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Hello everyone!!πŸ’

Are you confused with the titleπŸ˜…? Do you also stay away from regular expressions? Do you use google while solving regex problems? Not after reading this article!πŸ˜‹

C'mon, let's learn it together.πŸ€—

CONTENTS

Why Regular Expressions?

Regex(Regular Expressions) is used to define various types of string patterns which can be used for manipulating, searching, or editing a string. It can be used in all types of text search and text replace operations. Simply, a regular expression is a sequence of characters that helps us to match or find strings.

As we are now aware of regex, let's see how to write it.🀩

Cheatsheets

Matching Symbols

symbols.PNG

Note: [^regex] and ^regex are totally different.

Meta Characters

symbolsTwo.PNG

Quantifiers

symbolsthree.PNG

How to write regular expressions?

We should write a regular expression pattern in such a way that it satisfies the required output. Many of them feel regex is hard because of this. So, let's solve some examples to understand this more clearly.

disclaimer: I am using java methods in solutions below. If you are willing to use other languages just check with the regular expression, which is our main goal.πŸ˜‰

  • Question-1: Given string is "I love Hashnode. It is a wonderful platform." Write a matching regular expression that split the string into tokens.
    String s="I love Hashnode. It is a wonderful platform." ;  
    s=s.replaceAll("[^\\w]", " ");
    
    As we take only words as tokens we have to remove . after each sentence. So, we used [^\\w] in replaceAll() to replace all characters except [a-zA-Z_0-9] with a white-space. Now, to split them into tokens we doπŸ‘‡
    String[] str=s.split("[\\s]+");
    
    Here, we are scanning for a token until a white-space occurs. We identified white spaces using [\\s]. Since there can be a sequence of more than one white spaces we also used a +.

    slashs.JPG

Output: [I, love, Hashnode, It, is, a, wonderful, platform]
  • Question-2: Given a string "I l1ove Hashn7ode. It is 3a wond5erful pla4tform.". Our aim is to print only numbers from this string.
    String s="I l1ove Hashn7ode. It is 3a wond5erful pla4tform.";  
    s=s.replaceAll("[^0-9]", " ");
    
    Our aim is to get numbers right? So, I am replacing everything with a white-space expect 0-9 using [^0-9].
    s=s.trim();
    String[] str=s.split("[\\s]+");
    
    • Why we used trim()?

trim() is used to remove trailing and leading spaces. After replacing alphabets with a white-space, we get trailing spaces because of I in " I love Hashnode". Since trailing spaces cannot be identified with [\\s]+ we used trim().

Output:  [1, 7, 3, 5, 4]

That's all people😍. Now, we can write any regex patterns in any language by using these cheat sheets.

Say bye-bye to google!😁

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