POSIX Environment Variable Name (Uppercase Convention) Regex for PHP

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching posix environment variable name (uppercase convention), ported and verified for PHP. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your PHP project — whether you're validating in a Laravel validator, a WordPress plugin, or a standalone PHP script.

Php Implementation

<?php
// POSIX Environment Variable Name (Uppercase Convention)
// ReDoS-safe | RegexVault — Dev & Systems > Environment

define('POSIX_ENVIRONMENT_VARIABLE_NAME_UPPERCASE_CONVENTION_PATTERN', '/^[A-Z_][A-Z0-9_]{0,254}$/');

function validate_posix_environment_variable_name_uppercase_convention(string $input): bool {
    return (bool) preg_match(POSIX_ENVIRONMENT_VARIABLE_NAME_UPPERCASE_CONVENTION_PATTERN, $input);
}

// Example
var_dump(validate_posix_environment_variable_name_uppercase_convention("PATH")); // bool(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 PHP developers because especially relevant in PHP where PCRE backtracking limits can trigger silent failures on malicious input. 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

POSIX variables are case-sensitive and conventionally uppercase. Lowercase variables (PATH vs path) are different on Linux. On Windows, environment variables are case-insensitive.