Syslog Priority and Facility Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching syslog priority and facility, 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

// Syslog Priority and Facility
// ReDoS-safe | RegexVault — Dev & Systems > Log Parsing

const syslogPriorityAndFacilityRegex = /^<((?:19[01]|1[0-8][0-9]|[1-9][0-9]|[0-9]))>/;

function validateSyslogPriorityAndFacility(input: string): boolean {
  return syslogPriorityAndFacilityRegex.test(input);
}

// Example
console.log(validateSyslogPriorityAndFacility("<0>message")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > Log Parsing 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

Priority = facility * 8 + severity. Facility: 0=kernel, 1=user, 3=daemon, 4=auth, 16-23=local0-7. Severity: 0=emergency, 1=alert, 2=critical, 3=error, 4=warning, 5=notice, 6=info, 7=debug. Valid range 0-191.