Top 15 Commonly Used Regex

Regular Expressions aka Regex are expressions that define a search pattern. They are widely used for validation purposes, like email validation, url validation, phone number validation and so on.

Forming Regex:
A regex is written between two forward slashes (/) delimiters. These delimiters are essential only for certain Regex engines (JS,PHP..). It is then followed by 2 flags:

  • i : Ignore case Flag, ignores the case(uppercase/lowercase) of the input string
  • g : Global Flag, searches for multiple matches instead of stopping at the first match
 /* Regex Example */
 /hello/ig 
 /* will match the word "hello" irrespective of its case and 
    will return all found matches. */

A quick cheat sheet for those of you who do not remember all the rules of Regex

Regex

Cheat Sheet – Regex Rules

Character classes Quantifiers & Alternation
. any character except newline a* a+ a? 0 or more, 1 or more, 0 or 1
\w \d \s word, digit, whitespace a{5} a{2,} exactly five, two or more
\W \D \S not word, digit, whitespace a{1,3} between one & three
[abc] any of a, b, or c a+? a{2,}? match as few as possible
[^abc] not a, b, or c ab|cd match ab or cd
[a-g] character between a & g
Anchors Groups & Lookaround
^abc$ start / end of the string (abc) capture group
\b word boundary \1 backreference to group #1
Escaped characters (?:abc) non-capturing group
\. \* \\ \ is used to escape special chars. \* matches * (?=abc) positive lookahead
\t \n \r tab, linefeed, carriage return (?!abc) negative lookahead

Commonly used Regex

1. Digits

2. Alphanumeric Characters

3. Email

4. Password Strength

  • Complex: Should have 1 lowercase letter, 1 uppercase letter, 1 number, 1 special character and be at least 8 characters long
    /(?=(.*[0-9]))(?=.*[\!@#$%^&*()\\[\]{}\-_+=~`|:;"'<>,./?])(?=.*[a-z])(?=(.*[A-Z]))(?=(.*)).{8,}/ 
    
  • Moderate: Should have 1 lowercase letter, 1 uppercase letter, 1 number, and be at least 8 characters long
    /(?=(.*[0-9]))((?=.*[A-Za-z0-9])(?=.*[A-Z])(?=.*[a-z]))^.{8,}$/
    

5. Username

  • Alphanumeric string that may include _ and – having a length of 3 to 16 characters –
    /^[a-z0-9_-]{3,16}$/

6. URL

  • Include http(s) Protocol
    /https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{2,256}\.[a-z]{2,6}\b([-a-zA-Z0-9@:%_\+.~#()?&//=]*)/ 
    
  • Protocol Optional
    /(https?:\/\/)?(www\.)?[-a-zA-Z0-9@:%._\+~#=]{2,256}\.[a-z]{2,6}\b([-a-zA-Z0-9@:%_\+.~#?&//=]*)/ 
    

7. IP Address

/* Match IPv4 address */
/^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$/ 
/* Match IPv6 address */
/(([0-9a-fA-F]{1,4}:){7,7}[0-9a-fA-F]{1,4}|([0-9a-fA-F]{1,4}:){1,7}:|([0-9a-fA-F]{1,4}:){1,6}:[0-9a-fA-F]{1,4}|([0-9a-fA-F]{1,4}:){1,5}(:[0-9a-fA-F]{1,4}){1,2}|([0-9a-fA-F]{1,4}:){1,4}(:[0-9a-fA-F]{1,4}){1,3}|([0-9a-fA-F]{1,4}:){1,3}(:[0-9a-fA-F]{1,4}){1,4}|([0-9a-fA-F]{1,4}:){1,2}(:[0-9a-fA-F]{1,4}){1,5}|[0-9a-fA-F]{1,4}:((:[0-9a-fA-F]{1,4}){1,6})|:((:[0-9a-fA-F]{1,4}){1,7}|:)|fe80:(:[0-9a-fA-F]{0,4}){0,4}%[0-9a-zA-Z]{1,}|::(ffff(:0{1,4}){0,1}:){0,1}((25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])\.){3,3}(25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])|([0-9a-fA-F]{1,4}:){1,4}:((25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])\.){3,3}(25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9]))/
/* Match both IPv4, IPv6 addresses */
/((^\s*((([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5]))\s*$)|(^\s*((([0-9A-Fa-f]{1,4}:){7}([0-9A-Fa-f]{1,4}|:))|(([0-9A-Fa-f]{1,4}:){6}(:[0-9A-Fa-f]{1,4}|((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3})|:))|(([0-9A-Fa-f]{1,4}:){5}(((:[0-9A-Fa-f]{1,4}){1,2})|:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3})|:))|(([0-9A-Fa-f]{1,4}:){4}(((:[0-9A-Fa-f]{1,4}){1,3})|((:[0-9A-Fa-f]{1,4})?:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){3}(((:[0-9A-Fa-f]{1,4}){1,4})|((:[0-9A-Fa-f]{1,4}){0,2}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){2}(((:[0-9A-Fa-f]{1,4}){1,5})|((:[0-9A-Fa-f]{1,4}){0,3}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){1}(((:[0-9A-Fa-f]{1,4}){1,6})|((:[0-9A-Fa-f]{1,4}){0,4}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(:(((:[0-9A-Fa-f]{1,4}){1,7})|((:[0-9A-Fa-f]{1,4}){0,5}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:)))(%.+)?\s*$))/

8. Dates

/* Date Format YYYY-MM-dd */ 
/([12]\d{3}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01]))/

/* Date Format dd-MM-YYYY or 
               dd.MM.YYYY or
               dd/MM/YYYY
   with check for leap year */ 
/^(?:(?:31(\/|-|\.)(?:0?[13578]|1[02]))\1|(?:(?:29|30)(\/|-|\.)(?:0?[1,3-9]|1[0-2])\2))(?:(?:1[6-9]|[2-9]\d)?\d{2})$|^(?:29(\/|-|\.)0?2\3(?:(?:(?:1[6-9]|[2-9]\d)?(?:0[48]|[2468][048]|[13579][26])|(?:(?:16|[2468][048]|[3579][26])00))))$|^(?:0?[1-9]|1\d|2[0-8])(\/|-|\.)(?:(?:0?[1-9])|(?:1[0-2]))\4(?:(?:1[6-9]|[2-9]\d)?\d{2})$/

/* Date Format dd-mmm-YYYY or
               dd/mmm/YYYY or
               dd.mmm.YYYY */ 
/^(?:(?:31(\/|-|\.)(?:0?[13578]|1[02]|(?:Jan|Mar|May|Jul|Aug|Oct|Dec)))\1|(?:(?:29|30)(\/|-|\.)(?:0?[1,3-9]|1[0-2]|(?:Jan|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec))\2))(?:(?:1[6-9]|[2-9]\d)?\d{2})$|^(?:29(\/|-|\.)(?:0?2|(?:Feb))\3(?:(?:(?:1[6-9]|[2-9]\d)?(?:0[48]|[2468][048]|[13579][26])|(?:(?:16|[2468][048]|[3579][26])00))))$|^(?:0?[1-9]|1\d|2[0-8])(\/|-|\.)(?:(?:0?[1-9]|(?:Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep))|(?:1[0-2]|(?:Oct|Nov|Dec)))\4(?:(?:1[6-9]|[2-9]\d)?\d{2})$/

9. Time

10. HTML Tags

11. Javascript Handlers

12. Slug

  • Slug /^[a-z0-9]+(?:-[a-z0-9]+)*$/

13. Match Duplicates in a String

14. Phone Numbers

/* International Phone Numbers */
/^(?:(?:\(?(?:00|\+)([1-4]\d\d|[1-9]\d?)\)?)?[\-\.\ \\\/]?)?((?:\(?\d{1,}\)?[\-\.\ \\\/]?){0,})(?:[\-\.\ \\\/]?(?:#|ext\.?|extension|x)[\-\.\ \\\/]?(\d+))?$/

Note: Use regex for validating phone numbers only if you don’t have the choice to use a library. There are several libraries that handle phone numbers more accurately and should be used instead.

15. File Path

Additional Regexes

1. Zip codes

There is NO single Regex that can handle all zip codes given that zip codes around the world do not follow a common pattern. Here is a list that contains Regex specific to each country.

2. Payment Validation

Here is a link that contains regex for validating leading Credit cards like Visa, Mastercard and so on.

3. Identity Documents

  • Social Security Number – Ref
  • /* can use either hypen(-) or space( ) character as separator */
    /^((?!219-09-9999|078-05-1120)(?!666|000|9\d{2})\d{3}-(?!00)\d{2}-(?!0{4})\d{4})|((?!219 09 9999|078 05 1120)(?!666|000|9\d{2})\d{3} (?!00)\d{2} (?!0{4})\d{4})|((?!219099999|078051120)(?!666|000|9\d{2})\d{3}(?!00)\d{2}(?!0{4})\d{4})$/
    
  • Passport – /^[A-PR-WY][1-9]\d\s?\d{4}[1-9]$/

References

P.s. Need a graphical explanation of any of the above Regex ? Try Regular Expression Visualization and copy-paste any Regex in the input box to get a graphical representation of it. Hope that helps!

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