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

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

• Whole Numbers – /^\d+$/
• Decimal Numbers – /^\d*\.\d+$/
• Whole + Decimal Numbers – /^\d*(\.\d+)?$/
• Negative, Positive Whole + Decimal Numbers – /^-?\d*(\.\d+)?$/
• Whole + Decimal + Fractions – /[-]?[0-9]+[,.]?[0-9]*([\/][0-9]+[,.]?[0-9]*)*/

2. Alphanumeric Characters

• Alphanumeric without space – /^[a-zA-Z0-9]*$/
• Alphanumeric with space – /^[a-zA-Z0-9 ]*$/

3. Email

• Common email Ids – /^([a-zA-Z0-9._%-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,6})*$/
• Uncommon email ids – /^([a-z0-9_\.\+-]+)@([\da-z\.-]+)\.([a-z\.]{2,6})$/

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

• IPv4 address
• IPv6 address
• Both IPv4, IPv6 addresses

/* 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 using separator -
• Date Format dd-MM-YYYY using separators - or . or /
• Date Format dd-mmm-YYYY using separators - or . or /

/* 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

• Time Format HH:MM 12-hour, optional leading 0
  /^(0?[1-9]|1[0-2]):[0-5][0-9]$/
• Time Format HH:MM 12-hour, optional leading 0, Meridiems (AM/PM)
  /((1[0-2]|0?[1-9]):([0-5][0-9]) ?([AaPp][Mm]))/
• Time Format HH:MM 24-hour with leading 0
  /^(0[0-9]|1[0-9]|2[0-3]):[0-5][0-9]$/
• Time Format HH:MM 24-hour, optional leading 0
  /^([0-9]|0[0-9]|1[0-9]|2[0-3]):[0-5][0-9]$/
• Time Format HH:MM:SS 24-hour
  /(?:[01]\d|2[0123]):(?:[012345]\d):(?:[012345]\d)/

10. HTML Tags

• Elements with Attributes /<\/?[\w\s]*>|<.+[\W]>/

11. Javascript Handlers

• Inline JS handler /\bon\w+=\S+(?=.*>)/
• Inline JS handler with element /(?:<[^>]+\s)(on\S+)=["']?((?:.(?!["']?\s+(?:\S+)=|[>"']))+.)["']?/

12. Slug

• Slug /^[a-z0-9]+(?:-[a-z0-9]+)*$/

13. Match Duplicates in a String

• Search Duplicates /(\b\w+\b)(?=.*\b\1\b)/

14. Phone Numbers

• International Phone Numbers – with optional country code/extension

/* 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

• File Path with Filename and extension

/((\/|\\|\/\/|https?:\\\\|https?:\/\/)[a-z0-9 _@\-^!#$%&+={}.\/\\\[\]]+)+\.[a-z]+$/

• File Path with optional Filename, extension

/^(.+)/([^/]+)$/

• File Name with extension having 3 chars

/^[\w,\s-]+\.[A-Za-z]{3}$/

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]$/

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References

• https://www.codeproject.com/validate-passport-number
• https://gist.github.com/
• https://code.tutsplus.com/regular-expressions
• https://www.regular-expressions.info
• http://www.regexlib.com/
• https://projects.lukehaas.me/regexhub/
• http://wiki.zoolz.com/commonly-used-regular-expressions/
• https://www.smashingmagazine.com/advanced-regular-expressions/

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!