RegEx

Intro

Regular expressions are a language of their own. When you learn a new programming language, they’re this little sub-language that makes no sense at first glance. Many times you have to read another tutorial, article, or book just to understand the “simple” pattern described. Today, we’ll review eight regular expressions that you should know for your next coding project.
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

Commonly used RegEx

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]*)*/

Alphanumeric Characters

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

Email

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

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,}$/

Username

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

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@:%_\+.~#?&//=]*)/

IP Address

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

123456

/* 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*$))/

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 /

12345678910111213

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

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)/

HTML Tags

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

Javascript Handlers

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

Slug

• Slug
  /^[a-z0-9]+(?:-[a-z0-9]+)*$/

Match Duplicates in a String

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

14. Phone Numbers

• International Phone Numbers – with optional country code/extension

12	/* 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.

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}$/
  

Regex Tools

Resources

• https://www.debuggex.com/
• https://regex101.com/