Environment Variable Assignment (KEY=value) Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching environment variable assignment (key=value), 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

// Environment Variable Assignment (KEY=value)
// ReDoS-safe | RegexVault — Dev & Systems > Environment

const environmentVariableAssignmentKeyvalueRegex = /^([A-Za-z_][A-Za-z0-9_]{0,254})=(.*)$/;

function validateEnvironmentVariableAssignmentKeyvalue(input: string): boolean {
  return environmentVariableAssignmentKeyvalueRegex.test(input);
}

// Example
console.log(validateEnvironmentVariableAssignmentKeyvalue("NODE_ENV=production")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > Environment 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

Group 1 = variable name, group 2 = value (may be empty). An empty value (VAR=) means the variable exists with an empty value, distinct from an unset variable.