Unix Username Regex for JavaScript

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching unix username, ported and verified for JavaScript. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your JavaScript project — whether you're validating in an Express middleware, a Next.js API route, or a client-side form.

Javascript Implementation

// Unix Username
// ReDoS-safe | RegexVault — Dev & Systems > Shell

const unixUsernameRegex = /^[a-z_][a-z0-9_\-]{0,31}$/;

function validateUnixUsername(input: string): boolean {
  return unixUsernameRegex.test(input);
}

// Example
console.log(validateUnixUsername("root")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > Shell category and carries a ReDoS-safe certification. That matters for JavaScript developers because especially critical in long-running Node.js event loops where a ReDoS vulnerability can block the entire process. 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

Maximum username length is 32 chars on Linux. Usernames are case-sensitive on Linux. The www-data convention (hyphen allowed) is standard for web server accounts.