Go (RE2)

Password (No Special Chars) in GO

Go (RE2) can't run this pattern out of the box.

Try it in the GO tester →

Why it doesn't work in GO

Go's RE2 engine doesn't support lookarounds (`(?=...)`, `(?<=...)`, etc.) — they break the linear-time matching guarantee.

Approach

Restructure to capture the surrounding context as a group instead, or use JS / Python where lookarounds are available.

Workaround code in Go (RE2)

goGo (workaround)
package main

import (
	"fmt"
	"regexp"
	"unicode"
)

// RE2 doesn't support lookarounds. The fix: match a BROADER candidate
// without the lookaround, then verify the condition in Go code.
//
// Example: instead of `(?=.*\d)[A-Za-z\d]{8,}` (require a digit),
// match the candidate then check `HasDigit(s)` separately.

func HasDigit(s string) bool {
	for _, r := range s {
		if unicode.IsDigit(r) {
			return true
		}
	}
	return false
}

func main() {
	re := regexp.MustCompile(`[A-Za-z\d]{8,}`) // simplified, no lookaround
	input := "Password1 weakpass StrongerOne9"
	for _, candidate := range re.FindAllString(input, -1) {
		if HasDigit(candidate) { // the lookaround condition, in code
			fmt.Println(candidate)
		}
	}
}

Match a broader candidate without the lookaround, then verify the constraint in Go. Keeps the linear-time guarantee.

Pattern

regexGO
^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)[A-Za-z\d]{8,}$

How the pattern works

Three positive lookaheads (?=.*[a-z]) (?=.*[A-Z]) (?=.*\d) require a lowercase letter, uppercase letter, and digit somewhere in the string. [A-Za-z\d]{8,}$ then matches 8+ alphanumerics. Lookaheads are zero-width so they don't consume — they're constraints, not consumers. Note: Go's RE2 does not support lookaheads, so this pattern won't compile there.

Examples

Input

Password1

Matches

  • Password1

Input

MyPass99

Matches

  • MyPass99

Input

weakpass

No match

—

Same pattern, other engines

JavaScript / ECMAScript

Supported

See how this pattern looks (and behaves) in JavaScript's built-in RegExp.

Python (re)

Supported

See how this pattern looks (and behaves) in Python's stdlib `re` module.

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