Japanese Imperial Era Year (Reiwa/Heisei/Showa) Regex for Go

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching japanese imperial era year (reiwa/heisei/showa), ported and verified for Go. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your Go project — whether you're validating in a Gin handler, a gRPC service, or a command-line tool.

Go Implementation

// Japanese Imperial Era Year (Reiwa/Heisei/Showa)
// ReDoS-safe | RegexVault — Localization > Date Formats

package validation

import "regexp"

var japaneseImperialEraYearReiwaheiseishowaRe = regexp.MustCompile(`^(?:(令和|R)((?:[1-9]|[1-9][0-9]))|(平成|H)((?:[1-9]|[12][0-9]|3[01]))|(昭和|S)((?:[1-9]|[12][0-9]|3[0-9]|6[0-4])))年(0?[1-9]|1[0-2])月(0?[1-9]|[12][0-9]|3[01])日$`)

func ValidateJapaneseImperialEraYearReiwaheiseishowa(s string) bool {
    return japaneseImperialEraYearReiwaheiseishowaRe.MatchString(s)
}

// Example
// fmt.Println(ValidateJapaneseImperialEraYearReiwaheiseishowa("令和6年1月15日")) // true

Test Cases

When to use this pattern

This pattern is drawn from the Localization > Date Formats category and carries a ReDoS-safe certification. That matters for Go developers because Go's RE2 engine is inherently safe from catastrophic backtracking, but this pattern has been additionally verified for correctness. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Era limits: 令和/Reiwa started May 1, 2019 (max year currently ~6). 平成/Heisei: 1-31 (1989-2019). 昭和/Showa: 1-64 (1926-1989). Meiji and Taisho are pre-1926 and excluded here. Convert to Gregorian for storage.