Validation

Email Local Part (Before @)

Validate just the local part of an email address (the bit before the @).

Available in

JavaScript / ECMAScript code

jsJavaScript

const re = new RegExp("^[a-zA-Z0-9._%+\\-]{1,64}$", "");
const input = "john.doe";
const matches = [...input.matchAll(re)];
console.log(matches.map(m => m[0]));

Uses `String.prototype.matchAll` for global iteration (Node 12+ / all modern browsers).

Python (re) code

pyPython

import re

pattern = re.compile(r"^[a-zA-Z0-9._%+\-]{1,64}$")
input_text = "john.doe"
for m in pattern.finditer(input_text):
    print(m.group(0))

Stdlib `re` module — no third-party dependency. Works on Python 3.6+.

Go (RE2) code

goGo

package main

import (
	"fmt"
	"regexp"
)

func main() {
	re := regexp.MustCompile(`^[a-zA-Z0-9._%+\-]{1,64}$`)
	input := `john.doe`
	for _, match := range re.FindAllString(input, -1) {
		fmt.Println(match)
	}
}

Uses `regexp.MustCompile` (panics on bad patterns at startup) and `FindAllString` for all matches.

Pattern

regexengine-agnostic

^[a-zA-Z0-9._%+\-]{1,64}$

Raw source: ^[a-zA-Z0-9._%+\-]{1,64}$

How it works

^ and $ anchor to the full string. [a-zA-Z0-9._%+\-] is the conservative local-part character set (dots, underscores, percent, plus, hyphen for sub-addressing). {1,64} enforces the RFC max length for the local part.