Designing CLI Exit Codes and Error Messages

CLI exit codes distinguish success, input errors and operational failures for shell automation.

What It Does

CLI exit codes distinguish success, input errors and operational failures for shell automation. The following examples distinguish a normal use case, a boundary case and a practical application.

Requirements and Compatibility

PHP 8.x and a local test environment. Apply input validation, correct error handling and the requirements of any optional libraries.

The code focuses on the core concept. Production implementation may also need routes, validation, persistence, authorization or deployment tooling.

Example 1: Basic Behavior

Understand the primary operation and its inputs.

<?php
$argv = ['tool.php', '--task=export'];
$task = str_starts_with($argv[1], '--task=') ? substr($argv[1], 7) : '';
echo $argv[1]; // For actual parsing, call getopt() on the live CLI process

Example 2: Another Case

Check failure behavior or a different execution path.

<?php
$args = ['script.php', '--count', '5'];
$index = array_search('--count', $args, true);
$count = $index !== false ? filter_var($args[$index + 1] ?? null, FILTER_VALIDATE_INT) : false;
echo $count === false ? 'Invalid count' : $count;

Practical Example: Putting It to Use

Use documented nonzero codes so a scheduler can distinguish input and operational failures.

<?php
function exitCode(bool $valid, bool $available): int { if (!$valid) return 2; if (!$available) return 3; return 0; }
echo exitCode(true, false);

Important Behavior and Edge Cases

Write useful messages to stderr and do not leak secrets into logs.

Comparison with Related Functions or Approaches

Common Beginner Mistakes

Key Takeaways

• CLI exit codes distinguish success, input errors and operational failures for shell automation.
• Write useful messages to stderr and do not leak secrets into logs.
• A zero process exit status conventionally signals success.

Before adapting these examples, verify the return values, test the failure paths and confirm that your application meets its security and environment requirements.