Here is a collection of commonly used regular expressions for various tasks. You can use these examples to learn how to write your own regex or to copy and paste them into your projects.
Username (alphanumeric, 3-16 characters): /^[a-zA-Z0-9]{3,16}$/
Username (alphanumeric, with underscores and hyphens): /^[a-zA-Z0-9_-]{3,16}$/
Password (at least 8 characters, one uppercase, one lowercase, one number): /^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)[a-zA-Z\d]{8,}$/
Password (at least 8 characters, one uppercase, one lowercase, one number, one special character): /^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$/
Integer: /^-?\d+$/
Positive Integer: /^\d+$/
Negative Integer: /^-\d+$/
Floating-Point Number: /^-?\d*\.\d+$/
Positive Floating-Point Number: /^\d*\.\d+$/
Hexadecimal Number: /^[0-9a-fA-F]+$/
Date (YYYY-MM-DD): /^\d{4}-\d{2}-\d{2}$/
Date (MM/DD/YYYY): /^(0[1-9]|1[0-2])\/(0[1-9]|[12][0-9]|3[01])\/\d{4}$/
Time (HH:MM): /^([01]?[0-9]|2[0-3]):[0-5][0-9]$/
Time (HH:MM:SS): /^([01]?[0-9]|2[0-3]):[0-5][0-9]:[0-5][0-9]$/
Email: /^([a-zA-Z0-9_\-\.]+)@([a-zA-Z0-9_\-\.]+)\.([a-zA-Z]{2,5})$/
URL: /^(https?:\/\/)?([\da-z\.-]+)\.([a-z\.]{2,6})([\/\w \.-]*)*\/?$/
URL with query string: /^(https?:\/\/)?([\da-z\.-]+)\.([a-z\.]{2,6})([\/\w \.-]*)*\/?(\?.*)?$/
HTML Tag: /<([a-z][a-z0-9]*)\b[^>]*>.*?<\/\1>/
Phone Number (North American): /^(\+?1\s?)?(\(?\d{3}\)?[\s.-]?)?\d{3}[\s.-]?\d{4}$/
Credit Card (Visa, Mastercard, American Express): /^(?:4[0-9]{12}(?:[0-9]{3})?|5[1-5][0-9]{14}|3[47][0-9]{13})$/
IP Address (IPv4): /^((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/
IP Address (IPv6): /(([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]))/