Text Processingflags: g

Base64 String

Match Base64-encoded strings, including proper padding with = and == characters.

Available in

JavaScript / ECMAScript code

jsJavaScript

const re = new RegExp("(?:[A-Za-z0-9+\\/]{4})*(?:[A-Za-z0-9+\\/]{2}==|[A-Za-z0-9+\\/]{3}=)?", "g");
const input = "SGVsbG8gV29ybGQ=";
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+\/]{4})*(?:[A-Za-z0-9+\/]{2}==|[A-Za-z0-9+\/]{3}=)?")
input_text = "SGVsbG8gV29ybGQ="
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+\/]{4})*(?:[A-Za-z0-9+\/]{2}==|[A-Za-z0-9+\/]{3}=)?`)
	input := `SGVsbG8gV29ybGQ=`
	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+\/]{4})*(?:[A-Za-z0-9+\/]{2}==|[A-Za-z0-9+\/]{3}=)?   (flags: g)

Raw source: (?:[A-Za-z0-9+\/]{4})*(?:[A-Za-z0-9+\/]{2}==|[A-Za-z0-9+\/]{3}=)?

How it works

The pattern matches groups of 4 Base64 characters ((?:[A-Za-z0-9+\/]{4})*) then allows the trailing partial group: 3 chars + one =, or 2 chars + ==. This enforces valid Base64 padding rules.