Command-Line Flag (Short / Long) Regex for JavaScript

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching command-line flag (short / long), 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

// Command-Line Flag (Short / Long)
// ReDoS-safe | RegexVault — Dev & Systems > Shell

const commandlineFlagShortLongRegex = /^(?:--([a-zA-Z][a-zA-Z0-9\-]{0,49})(?:=(.+))?|-([a-zA-Z0-9])(.*))$/;

function validateCommandlineFlagShortLong(input: string): boolean {
  return commandlineFlagShortLongRegex.test(input);
}

// Example
console.log(validateCommandlineFlagShortLong("--verbose")); // 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

Short flags: group 3=char, group 4=combined value (e.g., -ofile.txt). Long flags: group 1=name, group 2=value after =. GNU getopt allows both --flag value and --flag=value.