How to Match Any Repeating Character Using Regular Expressions in Go?

In this article, we will address the challenge of matching any character that repeats twice using regular expressions in Go. This task is often straightforward in other regex syntaxes, such as JavaScript, where one can simply use backreference to match repeating characters. However, Go's native regular expression engine (re2) doesn't support backreference.

Can't Use Backreference in Go's re2

The provided JavaScript example leverages backreference to capture repeating characters:

var str = "abccdeff";
var r = /([a-z]{1})\1/g
console.log(str.match(r))

This pattern would fail in Go's re2 due to the lack of backreference support.

Alternatives to Go's re2

To address this limitation, consider these alternatives:

• Use a compatible regex library: Libraries like glenn-brown/golang-pkg-pcre offer advanced features, including backreference, and are compatible with Go's syntax.
• Implement a custom loop: Develop a loop-based solution that manually analyzes characters for repetition without relying on regex.

Example Custom Loop Solution

package main

import (
    "fmt"
    "regexp"
)

func main() {
    str := "abccdeff"

    // Find and print repeating characters without using regex
    for i, ch := range str {
        if i 1