Regex tutorial: matching an email

A great topic! Matching an email address using regular expressions (regex) can be a bit tricky, but don't worry, I'm here to guide you through it.

The Basics

Before we dive into the regex, let's cover some basic requirements for an email address:

1. It must start with a local part (the part before the @ symbol).
2. The local part can contain letters, numbers, dots (.), hyphens (-), and underscores (_).
3. The local part must be followed by the @ symbol.
4. The domain part (the part after the @ symbol) must contain at least one dot (.) and cannot be longer than 253 characters.
5. The domain part can contain letters, numbers, dots (.), hyphens (-), and underscores (_).

The Regex Pattern

Here's a regex pattern that matches most common email addresses:

^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$

Let's break it down:

• ^ matches the start of the string.
• [a-zA-Z0-9._%+-]+ matches one or more characters that are letters (both uppercase and lowercase), numbers, dots (.), hyphens (-), underscores (_), percent signs (%), or plus signs (+). This matches the local part.
• @ matches the @ symbol.
• [a-zA-Z0-9.-]+ matches one or more characters that are letters (both uppercase and lowercase), numbers, dots (.), or hyphens (-). This matches the domain part.
• \. matches a dot (.) character.
• [a-zA-Z]{2,} matches the top-level domain (TLD) which must be at least 2 characters long and contain only letters (both uppercase and lowercase).
• $ matches the end of the string.

Example Matches

Here are some examples of email addresses that match this regex pattern:

• [email protected]
• [email protected]
• [email protected]
• [email protected]

Example Non-Matches

Here are some examples of email addresses that do not match this regex pattern:

• @example.com (missing local part)
• john.doe@ (missing domain part)
• john.doe@example (missing TLD)
• [email protected] (extra dot in the domain part)

Tips and Variations

• To match internationalized domain names (IDNs), you can add the \x{00C0-\x{00FF} Unicode character class to the domain part.
• To match email addresses with non-ASCII characters, you can use the \x{0000}-\x{10FFFF} Unicode character class.
• To match email addresses with comments (e.g., [email protected] (comment)), you can add a separate regex pattern to match the comment.

I hope this tutorial has helped you understand how to match email addresses using regular expressions!