How can PHP be used to call subprograms similar to mainframes?

To call subprograms in PHP similar to mainframes, you can use PHP's built-in function `exec()` to execute external programs or scripts. This allows you to run separate scripts or programs as subprograms from your main PHP script. By using `exec()` with the appropriate command and arguments, you can achieve a similar functionality to calling subprograms on mainframes.

// Example of calling a subprogram using exec()
$command = "php subprogram.php arg1 arg2";
exec($command, $output, $return_var);

// Check the output and return value
if ($return_var === 0) {
    echo "Subprogram executed successfully!";
    print_r($output);
} else {
    echo "Error executing subprogram.";
}