Shell Variable Interpolation Regex for JavaScript

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching shell variable interpolation, 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

// Shell Variable Interpolation
// ReDoS-safe | RegexVault — Dev & Systems > Environment

const shellVariableInterpolationRegex = /\$(?:([A-Za-z_][A-Za-z0-9_]*)(?![A-Za-z0-9_{])|\{([A-Za-z_][A-Za-z0-9_]*)(?::-?[^}]+)?\})/g;

function validateShellVariableInterpolation(input: string): boolean {
  return shellVariableInterpolationRegex.test(input);
}

// Example
console.log(validateShellVariableInterpolation("$HOME")); // 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

Groups: 1=bare $VAR name, 2=${VAR} brace name. Shell parameter expansion operators: :- (default), := (assign), :? (error if unset), :+ (alternate value). Numeric positional parameters ($1, $2) are not matched.