Common Regex Patterns

Use the regexp package to compile patterns for email, URL, IP addresses, and phone numbers, then call MatchString to validate input. The following code defines common regex patterns and demonstrates how to test them against sample strings.

package main

import (
	"fmt"
	"regexp"
)

func main() {
	// Email: Basic pattern for local@domain.tld
	emailRe := regexp.MustCompile(`^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$`)
	
	// URL: Basic pattern for http/https with domain
	urlRe := regexp.MustCompile(`^https?://[a-zA-Z0-9.-]+(?:/[a-zA-Z0-9._~:/?#\[\]@!$&'()*+,;=-]*)?$`)
	
	// IPv4: Dotted decimal notation
	ipv4Re := regexp.MustCompile(`^(?:(?: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]?)$`)
	
	// Phone: US format (xxx) xxx-xxxx or xxx-xxx-xxxx
	phoneRe := regexp.MustCompile(`^\(?([0-9]{3})\)?[-.\s]?([0-9]{3})[-.\s]?([0-9]{4})$`)

	tests := map[string]func(string) bool{
		"email": emailRe.MatchString,
		"url":   urlRe.MatchString,
		"ipv4":  ipv4Re.MatchString,
		"phone": phoneRe.MatchString,
	}

	for name, fn := range tests {
		fmt.Printf("%s: %v\n", name, fn("test@example.com")) // Replace with specific test cases per type
	}
}

Regular expressions are text patterns that help you check if a string matches a specific format, like an email address or phone number. You define the pattern once, then use it to quickly verify if user input is valid before processing it. Think of it like a digital checklist that ensures data looks correct before you save it.