PHP bash glue (run php functions in bash)

functions.sh.php

#!/usr/bin/php
<?php
// how to include these bash functions in a bash script:
// eval "$(/usr/bin/php /path/to/functions.sh.php)";
declare(strict_types=1);
function quote($str)
{
    if (str_contains($str, "\x00")) {
        throw new \LogicException("null byte found in string");
    }
    return "'" . str_replace("'", "'\\''", (string)$str) . "'";
}
function echo_stderr(...$args)
{
    ob_start();
    foreach ($args as $arg) {
        echo $arg;
    }
    $output = ob_get_clean();
    fwrite(STDERR, $output);
}
$bash_functions = array(
    'test_php_to_bash_function' => function ($arg1, $arg2, ...$variadic_arguments) {
        echo "this function just test the bash<->php glue\n";
        var_dump(["arguments" => func_get_args(), "variadic_arguments" => $variadic_arguments]);
        echo "return value will be 99\n";
        return 99;
    },
    'validate_int' => function ($int, ...$variadic_arguments) {
        $max = null;
        $min = null;
        foreach($variadic_arguments as $argument) {
            if(str_starts_with($argument, "max=")) {
                $max = (int)substr($argument, strlen("max="));
            } elseif(str_starts_with($argument, "min=")) {
                $min = (int)substr($argument, strlen("min="));
            } else {
                echo "validate_int: unknown argument: ";
                var_dump($argument);
                echo "valid arguments: max=X, min=X\n";
                return 1;
            }
        }
        $validated = filter_var($int, FILTER_VALIDATE_INT);
        if ($validated === false) {
            echo "not a valid integer: ";
            var_dump($int);
            return 1;
        }
        if ($max !== null && $validated > $max) {
            echo "integer too large: $validated > $max\n";
            return 1;
        }
        if ($min !== null && $validated < $min) {
            echo "integer too small: $validated < $min\n";
            return 1;
        }
        return 0;
    },
);
// start bash<->php glue...
if (isset($argv[1])) {
    // execute the requested function
    $function_name = $argv[1];
    if (!isset($bash_functions[$function_name])) {
        echo_stderr("bash-php function $function_name not found\n");
        echo_stderr("available bash-php functions: " . implode(", ", array_keys($bash_functions)) . "\n");
        exit(1);
    }
    $arguments = array_slice($argv, 2, preserve_keys: false);
    $return_value = ($bash_functions[$function_name])(...$arguments);
    exit($return_value);
}
// no function requested, generate bash<->php functions glue
ob_start();
foreach ($bash_functions as $function_name => $php_callback) {
    echo "function $function_name() {\n";
    $reflection = new ReflectionFunction($php_callback);
    $parameters = $reflection->getParameters();
    $is_variadic = $reflection->isVariadic();
    $named_arguments = [];
    foreach ($parameters as $param) {
        $param_name = $param->getName();
        if ($param->isVariadic()) {
            // not naming this one, variadic arguments are generically passed as "$@"
        } else {
            $named_arguments[] = $param_name;
        }
    }
    foreach ($named_arguments as $argument_index => $param_name) {
        $index1 = $argument_index + 1;
        echo "\tlocal $param_name=\"\${$index1}\"\n";
    }
    if ($is_variadic) {
        echo "\tshift " . count($named_arguments) . "\n";
    }
    echo "\t/usr/bin/php " . quote(__FILE__) . ' ' . quote($function_name);
    foreach ($named_arguments as $param_name) {
        echo ' ' . "\"\${$param_name}\"";
    }
    if ($is_variadic) {
        echo ' "$@"';
    }
    echo "\n";
    echo "\treturn \$?\n";
    echo "}\n";
}
ob_end_flush();