Shebang Line Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching shebang line, 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

// Shebang Line
// ReDoS-safe | RegexVault — Dev & Systems > Shell

const shebangLineRegex = /^#!(\/(?:[a-zA-Z0-9._\-]+\/)*[a-zA-Z0-9._\-]+)((?:\s+[^\s]+)*)$/;

function validateShebangLine(input: string): boolean {
  return shebangLineRegex.test(input);
}

// Example
console.log(validateShebangLine("#!/bin/bash")); // 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

Groups: 1=interpreter path, 2=arguments. The env idiom (#!/usr/bin/env python3) is preferred for portability. The shebang must be the first two characters of the file.